Urgent - brake/turn signal problem.

[Bison]

Hi all,

As I write this, I'm sitting in the parking lot of a Canadian Tire, approximately 500 km from where I live.

I'm driving a 64 GMC 910 back, that I've had for about a week.

I've been having various electrical issues, the most important of which is that my rear brake and signal lights are acting up.

Earlier in the week, I replaced the brake light switch. They worked ok, but started acting up yesterday.

It started with the signals blinking really slowly (if at all ) with my foot on the brake.

I checked things over when it got dark, and this is what I've got:

-with the headlight switch off, the brake lights will come on but so dimly you can barely tell.
- if I then turn the headlights on, the brake lights turn off and won't come on no matter what.

I've checked all the connections to the headlight switch, checked the tail light bulbs/sockets, and cleaned and replaced the fuse.

Any suggestions?

I've searched this and come up with a few threads, but nothing is really definitive.

Thanks for any help.

[Coley]

Saskatchewan!
Great province....my wife's family is there!...now back to your situation.
There is a 75% chance this electrical problem is tied to a bad ground somewhere....everywhere, particularly on a 52 year old truck.
You have to work this through all of the possible grounding points for your lights.
You can always make an external ground wire with a good aligator clip or probe to do this.
Barring that....you might have a 1157 (dual element) bulb that has had its second filament break and spring over and touch the other element...which causes a world of weird lighting/circuit problems. Ask me how I know...lol.
However this is easy to check by simply substituting a new 1157 bulb everywhere whilst checking the electrical/lighting result.
However....start with the very very probable grounding problem.
All Good
Coley

[Bison]

So, if I cut the negative taillight wire and just ran it to the frame...could that do it?

[Coley]

Originally Posted by Bison

So, if I cut the negative taillight wire and just ran it to the frame...could that do it?

I don't think you have to go quite that far. If possible, I would leave the existing wires in place and simply bypass the existing negative wire(s) in order to test, as follows:
Get a length of wire to use as a ground and ensure very good authority of contact with both the light and the vehicle frame. That method will rule out that particular light for sure...and possibly both the rear. (note you can always, usually find a place where the ground wire 'might' be broken that you can tap into....but this on occasion can have problems too.
You can also simply try re-grounding all of the negative connections you find.
Do you know how to use a test light and check for power, voltage, continuity etc?
(...luckily if you are C.Tire...you aren't short of supplies...lol)

All Good
Coley

[Bison]

Ok, so after a couple hours checking and sanding grounds etc, I was getting frustrated and nowhere fast.

I pulled one of the taillight pods off, and grounded the mounting bolt to the stainless rear bumper.

Taillight lit up immediately. So then I went and bought a roll of wire, alligator clips, and o ring terminals.

Ran the wire from the bolt to the bumper mount on both sides.

It isn't pretty, or a real fix, but it will get me where I'm going (ie my garage/shop with a creeper, tools, compressor, etc)

I think re doing all the wiring will be in order soon...

[Big Kev-O]

The brakes and signals run through the turn signal switch inside the steering column. If the new ground wires don't solve you issues check out the column switch. The contacts inside the switch worn out and corroded which restrict the voltage running to the lights.

[Bison]

Update:

(First of all, Mods, could one of you change the thread title to 'Please help - rear turn signal/brake wiring issue'? - Thanks)

Second, I spent a couple hours today crawling around the truck checking wires etc. I think I'm definitely going to start saving for a rewiring kit, as everything is a hack job.

I found wire splices that started out one color, came out the other end of a splice another colour - and the heatshrink tubing over top wasn't 'shrunk' , so I could slide it over and find a 3" piece of another colour wire in the middle *sigh*.

Anyway, I pulled the fuse panel off the firewall, checked connections, and put it all back together. Did the same with dash board connections.

I went to go for a cruise, everything worked for a few minutes...but I didn't even leave the driveway before it blew another brake fuse.

I then found that wIth the headlight switch off, brake and signal lights would work and not blow fuses.

Went for my cruise, bought parts (including LED taillight bulbs, thinking they'd be less draw on the system), got home, installed them, and found that the rear passenger signal works fine, but the rear drivers side doesn't light up at all. Out came the multi meter - the drivers side is getting 9.something Volts, the right is getting 11 some odd.

Grounding the left taillight bucket with a jumper to clean metal didn't help.

I pulled the steering wheel, checked the switch, all the internal contacts are good.

Any suggestions? I find it odd that my brake/signals, dome light, and dash lights are all on the same fuse. Ive taken to using dash and dome lights as indicators. If they don't come on, I know I've lost brake lights...

[VetteVet]

Your problem seems to be that you are shorting the orange power wire in the fuse panel to ground through the dome light or the tail lights when you turn on the headlight switch. It is more likely that it is the tail lights or the front parking lights. One of those or the wires that feed them is probably shorted to ground.

below are three diagrams to show that this is possible.

This is the headlight switch and you can see the orange wire and the brown tail light wires. They make a connection when the switch is turned on.



This is the switch itself showing the brown wires and the orange wire.



This is the fuse panel showing the orange wire in the panel (bottom center) and if you follow it to the brake light switch and the headlight switch, you can see the connection between them and why a short in the parking light wires would cause the fuse to blow.

The orange wire also feeds the dome light, but if it was shorted then the fuse would blow anytime you opened the door or turned on the dome with the headlight switch.

What I am reading is that you only blow the fuse when the headlight switch is turned on.

Take your multimeter and check the tail light wires for continuity to ground with the headlight switch off. When you get very low resistance near zero on one of the lights then that is the grounded wire.

Most likely it will be one of the rear wires that run along the frame or at the rear of the truck where it has been rubbing the frame. If you can find the connector for the rear light wiring and disconnect it and you no longer blow fuses you know that the rear lights are where the short is located.

[davepl]

Whatever happened to the ability to delete a post? Am I missing it or did we never have it? Our own post, freshly edited I mean.

[Bison]

VetteVet - thanks for the reply and info. After I made my reply, I went out and dug into it again, checking the rear wiring.

I ended up finding the worst wiring rats nest I think I've ever seen:

[Bison]

1,2, and 3 were all connected to the truck harness.

4, 5, and 6 didn't connect to anything. When I got the miles of electrical tape off, they just hung into space.

7 and 8 went to one of the taillights

9 and 10 went to the other.

11 was for the license plate light.

7,8,9, and 10 were all just twisted together (and again onto the wires from the taillight buckets).

The twisted together joints were covered with electrical tape, but one joint would be taped up, then the wires held together and tape wrapped around both. The whole thing was taped up into a mass that was about 1.5" around, and 6" long, and was then stuffed up into the frame.

I took 4 5 and 6 to be 'indicators' of what color each wire was supposed to be, and redid everything with solder, heatshrink, and new full lengths of wire.