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Old 08-31-2018, 11:28 PM   #1
joeydurango
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I really hate electrical gremlins... gauge lights mystery

A new issue with my '72 Super... and I need some new ideas! I'm a bad electrician, so I'm muddling my way through with old posts on similar problems. But I'm out of material.

The gauge lights have functioned normally the entire time I've had this truck, with the exception of two occasions where the following problem showed up for a few seconds, then went away immediately. But the other day I drove home in the dark, and the problem appeared and hasn't gone away. So, I've gotta figure it out.

When the parking lights or headlights are turned on, all the gauge lights come on, but dimmer than normal. The turn signal indicators come on steady; the high beam indicator comes on steady; and when the turn signals are activated, the opposite indicator flashes along with half the dashboard.

I figured it was a grounding issue. So, I crawled under there and took a look at things. It's a tach panel, and the printed circuit is a newer replacement. Everything looks nice and tidy, maybe not factory, but not a rat's nest of splices. The cluster plug appears to have all the right colors in the right places. All the gauges and bulbs work. The factory ground clip on the dash is in place. All the factory printed circuit ground screws are tight (I loosened and tightened them all just to make sure they were getting good contact). Just for kicks, I ran a ground wire from various screws on the printed circuit and panel to the brake pedal bracket, trying the lights after each arrangement. No change.

Then, I thought maybe the cab wasn't grounding to the frame well enough. So, I ran a wire from cab to frame while trying various things under the dash. No dice!

Finally, I decided to check all the exterior light bulbs, although everything works normally - headlights, taillights, turn signals, reverse lights, brake lights, even the side indicators. I pulled all the lenses and checked to make sure the dual-filament bulbs didn't have a single burnt filament that was shorting the other one. Nope.

Another guy on the forum had the exact same symptoms recently, but he just needed to tighten a loose printed circuit ground screw. Now I'm just confused, and have no idea what to try next. Any electrical superstars out there?

Finally, since people like pictures, here's a little motivation to get those creative ideas flowing:
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Old 08-31-2018, 11:39 PM   #2
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Re: I really hate electrical gremlins... gauge lights mystery

Quote:
Originally Posted by joeydurango View Post
A new issue with my '72 Super... and I need some new ideas! I'm a bad electrician, so I'm muddling my way through with old posts on similar problems. But I'm out of material.

The gauge lights have functioned normally the entire time I've had this truck, with the exception of two occasions where the following problem showed up for a few seconds, then went away immediately. But the other day I drove home in the dark, and the problem appeared and hasn't gone away. So, I've gotta figure it out.

When the parking lights or headlights are turned on, all the gauge lights come on, but dimmer than normal. The turn signal indicators come on steady; the high beam indicator comes on steady; and when the turn signals are activated, the opposite indicator flashes along with half the dashboard.

I figured it was a grounding issue. So, I crawled under there and took a look at things. It's a tach panel, and the printed circuit is a newer replacement. Everything looks nice and tidy, maybe not factory, but not a rat's nest of splices. The cluster plug appears to have all the right colors in the right places. All the gauges and bulbs work. The factory ground clip on the dash is in place. All the factory printed circuit ground screws are tight (I loosened and tightened them all just to make sure they were getting good contact). Just for kicks, I ran a ground wire from various screws on the printed circuit and panel to the brake pedal bracket, trying the lights after each arrangement. No change.

Then, I thought maybe the cab wasn't grounding to the frame well enough. So, I ran a wire from cab to frame while trying various things under the dash. No dice!

Finally, I decided to check all the exterior light bulbs, although everything works normally - headlights, taillights, turn signals, reverse lights, brake lights, even the side indicators. I pulled all the lenses and checked to make sure the dual-filament bulbs didn't have a single burnt filament that was shorting the other one. Nope.

Another guy on the forum had the exact same symptoms recently, but he just needed to tighten a loose printed circuit ground screw. Now I'm just confused, and have no idea what to try next. Any electrical superstars out there?

Finally, since people like pictures, here's a little motivation to get those creative ideas flowing:

Engine to frame and engine to cab?

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Old 08-31-2018, 11:46 PM   #3
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Re: I really hate electrical gremlins... gauge lights mystery

See, this is what I mean about being a bad electrician. I assume you're talking about trying a ground wire from engine to frame and engine to cab. I can easily try that... but I had no idea that should be done, or how that could affect the dashboard lights. Thank you for the suggestion! I will try tomorrow morning and report back...
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Old 09-01-2018, 12:08 AM   #4
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Re: I really hate electrical gremlins... gauge lights mystery

Quote:
Originally Posted by joeydurango View Post
See, this is what I mean about being a bad electrician. I assume you're talking about trying a ground wire from engine to frame and engine to cab. I can easily try that... but I had no idea that should be done, or how that could affect the dashboard lights. Thank you for the suggestion! I will try tomorrow morning and report back...
Yes, there was a factory ground strap from the back of each valve cover bolt to the firewall and a ground strap from the engine block (by the fuel pump) to the frame rail on the passenger side.

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Old 09-01-2018, 01:29 AM   #5
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Re: I really hate electrical gremlins... gauge lights mystery

You can narrow it down by taking a jumper ground wire straight from the negative post on the battery to the tins on the gauge cluster but you said tach dash... sooo. Does the tach work? If yes I'm thinking bad light switch (resistor in the switch to dim or brighten dash lights by turning the switch knob). If no, then bad ground (seen this burn up tachs). Jumper wire from battery to cluster tins should confirm if the cluster isnt getting ground. Simple connections to check are 1.ground clip to dash- clean with sand paper to bare metal. 2.cluster wiring connector terminal to circuit board. 3. The connections Lockdoc mentioned. The gremlin that I can't wrap my head around is the turn indicator flashing opposite sides so I'm stumped on that one. Hmmmm.
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Old 09-01-2018, 03:54 AM   #6
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Re: I really hate electrical gremlins... gauge lights mystery

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You can narrow it down by taking a jumper ground wire straight from the negative post on the battery to the tins on the gauge cluster but you said tach dash... sooo. Does the tach work? If yes I'm thinking bad light switch (resistor in the switch to dim or brighten dash lights by turning the switch knob). If no, then bad ground (seen this burn up tachs). Jumper wire from battery to cluster tins should confirm if the cluster isnt getting ground. Simple connections to check are 1.ground clip to dash- clean with sand paper to bare metal. 2.cluster wiring connector terminal to circuit board. 3. The connections Lockdoc mentioned. The gremlin that I can't wrap my head around is the turn indicator flashing opposite sides so I'm stumped on that one. Hmmmm.
Most weird actions ['paradoxical movement' in medical terms] are caused by bad connections and shorts in and around the turn signal switch. It's inside the steering column. You'll have to pull the steering wheel to get to it. Careful to log positions and orientations of horn cap pieces so they get replaced in right order.
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Old 09-01-2018, 09:13 AM   #7
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Re: I really hate electrical gremlins... gauge lights mystery

As for the turn signal issue, is it possible that the turn signal switch is bad? Perhaps shorted out?
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Old 09-01-2018, 09:17 AM   #8
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Re: I really hate electrical gremlins... gauge lights mystery

If the turn signal switch was bad, would the turn signals themselves still work perfectly normally? Externally, everything works properly. It's just the gauge/dash lights that are screwy, suddenly.
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Old 09-01-2018, 11:54 AM   #9
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Re: I really hate electrical gremlins... gauge lights mystery

Okay, update time.

This morning I broke out the voltmeter, maybe I should have done that first. In any case, everything checks out fine. Engine is grounded; cab is grounded; bed is grounded. I pulled the panel plug and tested that - it grounds fine. I put the plug back in place and tested a panel ground with the panel fuse power - perfect. Everything appears to be normal... except, of course, that I still have the problem. Obviously I'm missing something.

I guess my biggest question right now is: Since everything works EXCEPT for *how* the gauge panel lights up, is it possible that it's the headlight switch or turn signal switch? I can't wrap my head around how one of those could be bad if all the external light functions work perfectly.

Edit: By the way, Leon, the engine wasn't grounded to the frame, but directly to the battery... it's a '90s-era crate replacement, so I guess they didn't redo all the connections by the book. But, everything does appear to ground well.
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Old 09-01-2018, 12:52 PM   #10
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Re: I really hate electrical gremlins... gauge lights mystery

I wonder about that. Turn signal switch would not affect instrument cluster lighting. Headlight switch would not affect turn signal indicator on the instrument cluster. But if you had to pick one or the other to try, headlight switch is inexpensive and reasonably easy to change out.

I wonder about you saying the gauge lights are dimmer than normal, is that with the dimmer turned all the way up? Is there any difference caused by wiggling the headlight switch knob?

Do you have any LED bulbs installed in the parking light housings or in the instrument cluster? If so can you take those out and put in regular bulbs to check how it behaves?

How about running jumper wires from battery negative terminal to the front parking light/turn signal housings, to make sure you have a good ground connection there. And jumper wire from the negative battery terminal all the way to the instrument cluster housing. See if that make it behave differently.
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Old 09-01-2018, 12:54 PM   #11
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Re: I really hate electrical gremlins... gauge lights mystery

Are you still having this problem? When the parking lights or headlights are turned on, all the gauge lights come on, but dimmer than normal. The turn signal indicators come on steady; the high beam indicator comes on steady; and when the turn signals are activated, the opposite indicator flashes along with half the dashboard.
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Old 09-01-2018, 02:53 PM   #12
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Re: I really hate electrical gremlins... gauge lights mystery

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Are you still having this problem?
Yep. That's the one. Still in full effect.

Thanks for your suggestions. I had already run a jumper from the battery to the panel; but I did take your suggestion to try the same to the front turn signal housings. I also just tested those grounds with my voltmeter. All are perfectly normal.

The headlight switch's dimmer does work, and doesn't affect anything when jiggled. Also, nothing changes through the steering range, lock-to-lock. No LED bulbs, just factory-style incandescents.

I have been into the column before (years ago), so if I need to replace the turn signal switch it's no big deal... but I don't like chasing problems with solutions I don't understand. But that might be where I'm at!

In short, everything I've tested is normal. Everything appears to be grounding solidly. All exterior lights operate normally. All interior bulbs and gauges are functional. It's just the super-strange way the panel lights began showing a week ago, with no obvious changes to anything beforehand.

Hence:
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Old 09-01-2018, 03:05 PM   #13
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Re: I really hate electrical gremlins... gauge lights mystery

Okay...here is a annoying, troubling electrical light situation I once saw and experienced through a lot of frustration..AND...it wasn't anything to do with grounding:

I had very weird lighting situations coming in my vehicle....the wrong lights working on the wrong circuit...and then stopping others, lights going out, coming on, under various electrical events, etc.
I re-grounded everything and it still wasn't working or changing anything.

I was ready to completely ready to re-wire the major lighting and screw the rest.

Guess what it was?......lol.
It was one of the filaments in one of the 1157 (dual filament) light bulbs.
It had broken and shorted/touched across the other filament circuit inside/within the bulb itself.....which needed some close visual inspection to actually see.
This produced all sorts of weird results by providing a brand new path for the electricity through the other regular circuit....

Anyhow, long story shortened....I replaced that 1157 bulb (checked the rest) and my problem immediately was gone. Cheap, quick, simple....but damn it had me going and confused for weeks.

....so, maybe take a quick look at your 1157 (dual filament) bulbs around the perimeter of the truck and make sure you don't have this situation.
Easy to check...

My two bits.
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Old 09-01-2018, 03:20 PM   #14
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Re: I really hate electrical gremlins... gauge lights mystery

Thanks, Coley. Believe it or not, I already looked at that! (I had seen that same issue in another thread.) Pulled the lenses off the four turn signals (the only 1157's, right?), visually inspected while off, and for good measure, visually inspected with parking lights and turn signals on, so I could actively see each filament doing its job.

I just took a look at the headlight switch. It looks like a newer replacement, probably done at the same time as the tach install and new printed circuit (at least several years ago, before I owned the truck - but not tons of use).

I think I'll pull the steering wheel next, take a look at the signal switch. Arg. Gotta love these old things. My wife claims I love it when something goes wrong with the truck... I kind of agree until it actually happens...
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Old 09-01-2018, 03:52 PM   #15
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Re: I really hate electrical gremlins... gauge lights mystery

Quote:
Originally Posted by joeydurango View Post
Okay, update time.

This morning I broke out the voltmeter, maybe I should have done that first. In any case, everything checks out fine. Engine is grounded; cab is grounded; bed is grounded. I pulled the panel plug and tested that - it grounds fine. I put the plug back in place and tested a panel ground with the panel fuse power - perfect. Everything appears to be normal... except, of course, that I still have the problem. Obviously I'm missing something.

I guess my biggest question right now is: Since everything works EXCEPT for *how* the gauge panel lights up, is it possible that it's the headlight switch or turn signal switch? I can't wrap my head around how one of those could be bad if all the external light functions work perfectly.

Edit: By the way, Leon, the engine wasn't grounded to the frame, but directly to the battery... it's a '90s-era crate replacement, so I guess they didn't redo all the connections by the book. But, everything does appear to ground well.

Lots of time people don't take the time to reconnect all of that stuff, or maybe the ground strap was bad and they didn't have a replacement. I'm not sure where you go from here on the problem. It's hard for me to visualize some of that stuff without being there to check it out first hand.

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Old 09-01-2018, 05:14 PM   #16
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Re: I really hate electrical gremlins... gauge lights mystery

Thanks, Leon. I appreciate the suggestions you had. This is a weird one, that's certain. I guess I'll just take a few stabs in the dark at it!
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Old 09-01-2018, 10:29 PM   #17
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Re: I really hate electrical gremlins... gauge lights mystery

Use a 12 volt tester and with a good ground carefully check both sides of one of the bulbs while it is still plugged into your dash. I would bet one side will be bright on your tester and on the other side of the bulb will be dim (bad ground ) I am sure it is a bad ground at the 1/4 inch screw on the printed circuit. That one screw grounds 3 of the 4 dash lights AND both of your turn signal lights on the one circuit on your printed circuit. I had to play with mine to get it to work. Also mine was a new printed circuit from LMC
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Old 09-01-2018, 10:35 PM   #18
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Re: I really hate electrical gremlins... gauge lights mystery

That one screw is the one slightly above and by the corner of your speedometer. You can access it while it is all together in the truck. I spent many nights after dark so I could see the dash lights with a mirror on the seat while laying on the floorboard messing with it.
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Old 09-01-2018, 10:42 PM   #19
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Re: I really hate electrical gremlins... gauge lights mystery

Thanks, Rick. Yep, I've been laying down there with a mirror too! Whole lot easier than getting up over and over.

I've been concentrating on the ground screw to the left of the panel plug... although I did loosen and tighten the one by the speedo too. I'll pay some more attention to the one you're talking about. It sure sounds just like the problem you had.

I'm not sure how to test each side of the bulb while it's still plugged in... do I need to partially disengage the bulb socket? I have a voltmeter with some small probes. Or, can I simply touch the visible trace on the surface of the printed circuit?

Thanks for the help - I'm making a big pot of chili right now but was planning on taking the column apart tonight or tomorrow. I'd much rather try what you're suggesting.
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Old 09-01-2018, 10:57 PM   #20
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Re: I really hate electrical gremlins... gauge lights mystery

There are 2small metal tabs that come in contact with the circuit ribbon on the light socket that twists into the back of the panel. Put your alligator clip from your tester someplace on the dash that you know is grounded. Then with your lights on check both sides of the bulb with the small pointed end of your probe. Kinda hard to get to but it can be done. If you check the ribbon itself and go through the back side you can burn up that circuit so be extremely careful. One side of the bulb should be right the other side (ground) should not light up. If it does then no ground on that circuit (the screw)
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Old 09-02-2018, 12:45 AM   #21
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Re: I really hate electrical gremlins... gauge lights mystery

You have to be careful not to poke the tester through the printed circuit, especially if it is a sharp pointed tester like mine that is made for poking through wire insulation. What you're dealing with is the metal case of the instrument cluster, which is grounded, then a thin layer of plastic, then the thin foil trace on the plastic, then the metal tab of the bulb holder or of the cluster plug, then plastic bulb holder or plastic cluster plug. So it is a 5 layer sandwich that is all pretty much wafer thin. Except where the bulb holder contacts, screw hole ground points, and cluster plug tabs make contact to the traces, the traces are coated with another layer of insulating plastic. The trace on one side of each bulb is supposed to be grounded anyway, but the other side is 12V feeding the bulb so you don't want to short the trace through the thin plastic to the ground of the metal instrument cluster case. Check that you have a 3A or smaller fuse (and not 5, 10, 20 A, etc.) in the top right PNL LTS position of your fuse block. That will provide some protection for the printed circuit, but only for the gauge illumination lamps. The direction signal lamp traces are unfused, so get unlimited current.

I don't want to discourage you, you need to go ahead, because Rick is on the most likely path and has provided some excellent info. If the printed circuit manufacturer didn't do a great job of making sure the traces around the screw hole ground points can make good electrical contact with the screws, those appropriate traces won't be connected to ground reliably and could cause the problem. My 2 cents.
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Old 09-02-2018, 12:55 AM   #22
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Re: I really hate electrical gremlins... gauge lights mystery

Just a tidbit more: If the previous owner did something wild like paint the metal case of the instrument cluster, or if the metal case of the instrument cluster is rusty, you could have just the screw threads making poor contact to ground (at those particular points where the screws attach the ground traces on the printed circuit to the instrument cluster). Or painted screws could cause that problem because they don't make good electrical contact.
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Old 09-02-2018, 02:48 PM   #23
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Re: I really hate electrical gremlins... gauge lights mystery

It works!

Rick, you were on the money from the get-go on that previous thread I tacked onto. Thanks to you and dmjlambert for the final pieces of the puzzle, and for everyone who helped out.

I had futzed with that ground screw earlier - one of the first things I did - but I guess not enough. Today I pulled it out, cleaned it (didn't even look dirty), and snugged it back down again... and of course then everything worked like normal. I felt like it must have been something simple, and it was. Unfortunately, the second go-round didn't happen until I spent at least a couple hours screwing around with everything else mentioned above. Oh well, I learned some things, and that's worth it to me.

Thank you all again. And for future forum searchers - if you have odd panel light issues, make *certain* via measurement that the grounds are good before heading off on a wild goose chase, like I was about to do.

This forum is wonderful!

EDIT to make things clearer for future searchers: I did test the grounds earlier, as mentioned, and everything appeared to be fine. What I missed (remember, bad electrician here) was that the printed circuit has multiple circuits, so multiple grounds that aren't redundant. I tested the fuel-gauge-side ground, and tested the panel tin itself, and tested the panel plug and dash clip and frame and cab and bed and engine and signal housings... sheesh... but apparently missed actually *testing* the one ground that mattered for that part of the panel. I feel sorta dumb for that. But, learning is good.
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Old 09-02-2018, 03:26 PM   #24
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Re: I really hate electrical gremlins... gauge lights mystery

I learnt something too, seriously glad you figured it out, a lot of great help along the way. Multiple grounds in the bezel, that, I did not know.....Thanks for sharing..even tho it was painful.
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Old 09-11-2018, 07:30 PM   #25
Mike_The_Grad
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Join Date: Oct 2013
Location: Santa Paula, CA
Posts: 576
Re: I really hate electrical gremlins... gauge lights mystery

This might be what im experiencing. I did have my cluster out about a month ago to paint the gauge needles and clean up the lens. When I reassembled the cluster I was trying to be cautious and not over torque the small screws that hold the gauges in and the printed circuit on to the housing. I remember having one of the printed circuit ribbons come loose from the circuit plastic right where the cluster harness connector plugs in, so I put a very small drop of super glue to backside of the ribbon and held it into place with a pencil eraser until it dried and never thought twice about it... this thread is awesome though, thanks to all who replied.
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