Electrical Troubles - C10 Chevy 1971

[drivingslow]

Dear Board,

Outstanding reading your various posts over the last week.

Very helpful.

I used to post long ago on a 62 Chevy Bel Air board.

I now picked up an interesting Chevy C10, and after some work, had it running smoothly for 8 months.

A 350, automatic, 2wd, etc.

The P-Owner unfortunately spliced a number of items into the electrical.

So suddenly on a colder night, the pickup would not turn over the following day, after running perfect.

Would not even make a 'click' with solenoid jump. Battery tested perfect. Found it to be a major ground problem. Tested with a 'poor man' jumper cable to negative battery terminal, to frame for a real ground, and it started right up.

After cleaning several grounds, having the truck start up fine again, with headlights working, noticed heater fan switch, turn signals, hazard, cig lighter, only produces a GEN ALT light. not working at all...

Tried repeatedly to find the short, or ground problem, but simply cannot.

Any ideas?

your help would be greatly appreciated.

is this just a failure to ground in the dash?

thank you.

[drivingslow]

help !

hehehe...

any thoughts at all?

[Luvlegs]

I need a suggestion too - I have the EXACT same situation but I only have 2 days left to get mine moved!

[Cobraguy]

I had a similar problem with my '70, I threw in the towel and replaced the entire wiring system with a Painless wiring kit.

[VetteVet]

There's a junction block on the passenger fender by the battery where the 12 volt feed wire from the battery joins with another wire that goes to the firewall junction block by the master cylinder. Take this wire off the junction block and clean all the terminal ends and the junction block and see if that helps.
Also another source of trouble is the external voltage regulator wire terminals.Clean those also and make sure the small wire that grounds the regulator to the radiator core support has a good connection.
There's probably a dozen other causes for this problem but these are two common ones.

[drivingslow]

thanks Cobraguy, had a feeling this is going to be needed, as it is getting close to the last option.

sorry Luvlegs, wish i could help you as well.

i am going to try to add a few more grounds, in the dash, double check some of the parts involved, like the heater switch, and maybe find yet another regulator to test.

if anyone has another suggestion, please let me know.

thanks again.

[drivingslow]

VETTE VET !

thank you indeed. all i needed was a tip to get me to keep looking, for i was thinking i was searching in vain.

Kalamazoo rocks in my book.

thanks again.

[tubbed 68]

Check the simple things fuses. Or make sure your ignition switch hot wire is hot.Get a test light make sure it is grounded first and then start grounding stuff and see if it helps maybe.Im not to fimiliar with the stock wiring harness.

[drivingslow]

nothing...

no luck what so ever...

still stumped.

done everything, almost three times...

[72lb4x4]

Well, if the truck starts, you're getting power from the battery to the fuse block from the battery... If the accessoriyes aren't working, it sounds like something in the area of the fuse block is no longer connected.

I'd get a manual and look at the wiring diagram to see if something common to the not working bits can be found.

I'm not suggesting that this is easy (it often isn't), but I'd expect it to be easier that rewiring the whole truck.

[WorkinLonghorn]

After cleaning several grounds, having the truck start up fine again, with headlights working, noticed heater fan switch, turn signals, hazard, cig lighter, only produces a GEN ALT light. not working at all...

OK.The hazard and turn sigs are on one circuit. Cig is the fuse to the left of that.Heater fan is left and lower to that.If it was me,I'd disconnect the battery and lossen the fuse panel (I think it's one screw),pull it apart and see which wire(s) is loose.
>>My last truck had been monkeyed with and I had to re-do some of the crappy splices,and crimp on some fresh connectors etc.It's really a piece of cake.
>>Don't start looking for a good cliff just yet.
>>Of course you check the fuses too and you might try just pushing the wires in from the engine side to see if you get momentary completion of some of those cicuits.
Now if still no joy,break out the volt meter and check that each fuse listed above is hot (ground one lead and touch hot side of fuse or either side if you have good fuse.If good,follow the wire to were the previous owner made some pathetic joke of a splice and repair it.But since you have multiple circuits suddenly out,it should be very obvious when you look at the panel backside.

[drivingslow]

thank you both...

72lb4x4
and
WorkinLONGHORN!

i have studied the wiring diagram forwards and back 72lb4x4!

just having some folks, give some additional insight, helps stop the idea you are searching in vain. your responses, and tips are sincerely appreciated.

WorkLH: will do the fuse box pull next, thanks.

updating on the search...

tonight was a cold cold one, and i thought i had it licked, finding an old burnt wiring splice connection, but having it properly repaired, the trouble still exists.

after all the grounds were cleared, a new regulator, i now have hazards.

but the heater switch, turn signals, wiper switch, cig lighter, still light up a 'alt gen' light.

there is simply no power to these items.

i have power to the red leading to the regulator, and on the red leading to the connections to the fuse box in the engine compartment.

i know my altenator is charging fine, but shouldn't i have other power in the other wires, like blue, white, etc., as well coming from the regulator?
(or do they power only when the acc. is turned on?)

i am a little tired, sorry, long day.

one of the strangest items, when the v. regulator is properly grounded, the alternator light comes on when key is turned, and stays on (and i know it is charging-working alt).

and when the ground is removed, the alternator light works properly, disappearing after ignition, and only light with turning on various acc. such as wiper, fan, sigs, etc.

used a test light on this voltage regulator ground connection, and it is seemed far too powerful to be merely a ground.

it sounds odd, and i fear the previous owners (a few i am certain), spliced and switched something ugly.

the wild thing is, had it working fine for several months until winter hit. thus i imagined it was a bad ground, or connection, not being wrongly wired.

[WorkinLonghorn]

I don't think it's wise to run the alt.with the ground wire disconnected.Really,I think it could ruin it.Just check that you have 12.5-14.5 AT THE BATTERY while running.If so you can forget about the alternator/regulater.If you have the warning light on and some circuits don't work then I think you have a short circuit. I hope you have a volt meter.Approch the prob;lem systematically.Follow the known good wires until you find the problem.You'll see how easy it is when you look at the fuse panel.
>>Hey it sure beats finding a problem on a '06 anything!

[drivingslow]

thank you WORKINLONGHORN again...

the battery while running, tested fine at 14.0

i did forget about the alternator and reg, and went to find - clean all the grounds and look for loose connections.

i do have a volt meter and will use it more often now.

but i did find it strange, so much power would be draining in the regulator ground.

later, after work, going to tackle what is behind the fuse box.

could a short be caused by a bad rear bulb?

even if they light and look clean?

i will continue to look...

but appreciate any additional tips.

thanks

[1971LT1SWBPOSI373]

Take a look at the wiring diagram, the engine bay side. The prints are listed in the FAQ section above. Wire 12R coming from your alternator/generator and going to the voltage regulator and then to the back of the fuse block also ties in with 18B/W at the bottom of the page. If you follow 18B/W toward the fuse block you'll see a fuse, but I'm most certain that's not a fuse but rather a fusable link. I can't really tell, but it appears 18B/W provides power through the block buss bars for some of the accessories. If this fusable link is blown-it could be your problem.
Another way to start nailing this down is to "ring" wires. Although not particularly fun to do it gets results quickly. Start your truck and take voltage readings coming from the back of the alternator following 12R to the fuse block, voltage reg, and battery. Remember your not looking for 12v (battery voltage) yor looking for 13.5 volt alternator voltage.
If your getting it into the cab, then head for the key switch. Occasionally bad contacts drop the voltage here. Let us know what you find.

[drivingslow]

thank you sincerely 1971LT1SWBPOSI373...

i will try your suggestions tomorrow.

pulled the fuse box apart, and it is fine - gave it a good cleaning.

checked cleaned connections in the dash, including headlamp switch (which really needed it - dimming dashlights now an ease).

lights bright as can be now...

rechecked connections to fan, and even examined the heater switch.

if you could see the truck now, it is basically pulled apart.

runs like a top, but i still cannot get the heater, turn sigs, lighters, wipers, only turn on the alt gen light.

still looking, thanks for the tip...

[paaw]

try moving you wires around by the fan switch happen to me and I shook the wires around the heater swith and ignition switch, and mine started back working just reach under the dash, my radio, turn signal, heater and wipers didn't work just a suggestion

[kbs71]

The wiring diagram shown is for a idiot light dash not a gauge dash. You don't mention which you have but it really isn't relevent. Just as to how the under dash wiring is hooked up to the gauge cluster. The 18B/W wire that runs from the 4 way splice with the 12R wires goes to the AMP meter there is also a 18B wire coming from the junction block at the battery. They both have short, I think 2 amp fuses in them. Like I said they go to the AMP gauge on the Gauge cluster or to the GEN light on the lights cluster. If one of these fuses is blown, you will get the GEN light on all the time.
Also the 16W and the 16DBL will only power up when the altenator is charging, so if you alt isn't charging they shouldn't have power.

I know this is kinda long, but I'm just trying to explain how the wiring works.

If you follow your 12R wire after it leaves the back of the firewall connector under the dash, it goes to another 4 way splice. You may have a problem there. If not I would bet the start switch is bad. That's the only thing all these items have in common. I've seen it happen before.
Most of the grounds for these trucks come from the motors or whatever the switch goes to. The wiper motor is grounded thru the case, the heater fan is grounded thru the case etc.
Do your brake lights work? If they do, you probably don't have a bad ground for the turn signals, as they would be the same. Like I said, I'd try a start switch, and I'd bet that's your problem. If you look you have a 12BRN wire off the back of the start switch that goes to the fuse block and powers the wipers, turn signals and the heater switch.

So to sum it up, change the start switch, because I believe it isn't powering the fuse block for those three items and check those inline fuses in the 18B and 18B/W wires. They are located @ a foot from the terminal and the splice.

Hope this works, if not, let me scatch my head some more over this.

[drivingslow]

THANK YOU THANK YOU...

KBS71

Eureka!

thanks as well 'paaw' and all who responded with some insight.

the start switch was a great tip for focus.

the switch itself is fine, but the connector plug, with the brown line, wasn't connecting properly to the starter switch.

when inspected 'twice' prior, it looked fine, and was cleaned, but i didn't see the clip slide back - just enough to not connect, when the entire plug was installed.

if it weren't for this board, i probably would still be lost.

thank you.

[gouldie]

this thread is full of helpfull information. i'm gonna be going through the wiring on my truck tomorrow to try and get the tail lights to work. some reason only the right blinker will work but only when the headlights are on.

i pulled out about a page of info that i'm gonna print out and have sitting next to me when i try to solve the problem.

[drivingslow]

good luck gouldie...

i know grounds are essential and two of them are directly connected to each rear side running lamps. a quick clean, to make sure the ground has sound metal connection, will improve electrical performance to the rear. both probably exposed to moisture for years back there.

clearly pulliing both back bulbs, cleaning the two rear sockets is essential.

but many on this board have referenced the need for sound grounds from the dash to frame - firewall.

best wishes.

[DangerDan]

No trouble (yet) but I have disassembled my 71 C10 have the wiring harness out as well as everything else except the glass, with all the switches and anything that plugged into it back left in place. The harness appears to be in great condition and everything worked fine.
Couple questions:
What should I use to clean all the contacts, is there any other checks to do before reinstall?

Is there a good website for electrical info.

Also I read this thread completely, some great help here. I see that wiring diagrams are available I can not find them can someone point me in the right direction tried to find them in the faq section.

OK a few questions...Thanks in advance!!

[c10fanatic]

I have a 72 GMC C25 with a 4.1L I6 three in the floor. my holder for the battery broke and it fell over causing the battery to arc. I didnt find out till i was stranded in town and the ignition switch quit working. But I bypassed the starting procedure with the switch by engaging the solenoid manually and it starts right up. Anyone have any suggestions to fix this problem.

[tino0217]

Check wire gauge, make sure not too much or not enough. Although i don't wanna go through each wiring for corrosion probably save the time and stress and buy new harness