Wiring gremlins.. turn signals

[pdxmac]

Just got a "new" 86 3/4 2wd that I am going to be using for my Handyman business and I'm trying to get her up to snuff.

Most of his problems are electrical, and the most pressing one is that the turn signals will not work when the headlights are on. They work fine when they are not, but when the headlights are on, the right side( front and rear, as well as the dash indicator) all go hot and stay that way.

I am thinking that there must be a short circuit somewhere that is feeding voltage from the headlight circuit to the right side turn signals, but I'm not finding and areas that could be causing this.

Has anyone had this problem? or have any ideas of where to look?


Thanks!

[Russell]

When you say that the lights go hot, are they at full brightness, or are they only kinda there?

It is possible that your headlight's grounds are shot (usually bolted to the core support just above the headlights), and that they are grounding through your signal lights or something instead.

Grounding problems always have interesting symptoms


Oh, and by the way, Welcome to the forum!

[pdxmac]

Thanks!

Well, I've spent the morning tracing wires and having the dash apart etc. I've isolated the problem to the left side marker lamp circuit. It is feeding into the right turn signal, and vise-versa. The left side marker lamps are not on full power though, probably about half power when the right turn signal is on. With the marker lamps turned on, the right turn signals are on full power.

Hopefully that makes sense

Things I've tried:

- Switching the light switch
- disconnection the main harness connector at the firewall to see if it is in the dash.
- disconnected the gauge cluster to see if it's in the guages/and or lighting
- removed various bulbs in the system to see if one of them is shorting.

[Russell]

Yep, definitely a grounding issue...

There are a couple grounds to look at -- should be 2 - 3 ground wires on the driver's side, and two on the pass side. Don't count your tail-light's ground out either, its located behind the lense on the driver's side.

Finally, check the ground down under the dash, where it hooks up to the e-brake cable housing.

If all those grounds are good, then something is shorting out against something else, make sure you check all of the dual filament bulbs in the truck (tailights, and signal lights)

[pdxmac]

Ok thanks!

Do you know where I should look for the grounds? I know there are two on the core support, I already cleaned and checked them, and there's the one bohind the driver's side taillight you told me about. I dont' know where the others are..

Thanks for all the help!

[Russell]

All of the front clip wiring grounds are on the core support -- There should be eyelets on both sides of the core support, bolted up in the same basic position. Its pretty common for the ground wires to break off the eyelets.

The only ground inside of the cab is the one that bolts up to the e-brake.

Other than that, there are ground straps from the battery to the engine, engine to the frame, and frame to the cab.

[pdxmac]

Ok, I've gone through all of the grounds.. no dice. There has to be a place that current is crossed somewhere and I just can't find it. I've tried disconnecting the whole gauge panel thinking it might be in there. Nope. Tried a new headlight switch. Nope. Tried removing each bulb in the system. Nope. Tried replacing all of the bulbs. Nope

Running out of ideas.. I am out of ideas I guess.

When the headlights are off, the turn signals work, but when the right side signal is on, it lights up the marker lights at like half intensity. And backwards, when the marker lamps/headlights are on, the right signals go hot and steady.

I am dumbfounded!

[Russell]

That is most certainly a strange bug...

Have you considered just replacing all of the wiring in the truck? Believe it or not, but its actually very easy to do, takes about 30 minutes to pull a harness, and maybe another hour to put it back in. That'd replace your entire cab harness, and your entire front clip harness.

There would be no need to replace your engine or tail-light harnesses, as both seem to be good.

Any wiring harness from 83(ish) through 86 should bolt straight into your truck. Just make sure that your donor truck has the wipers and headlight switch on the steering column like your truck has. Any special wiring that your truck has for courtesy lights, power windows / locks etc are independant from the rest of the truck's basic wiring.

[pdxmac]

No, I hadn't really thought of that.. I have narrowed down my search however. I know that the voltage is coming through the ground wires for the marker lights. I figured this out with a tester, and then cut the brown wires that lead to the front and rear marker lights, and it no longer crossed over.( I re-spliced them afterward) The right side signals still went hot when the headlights were turned on though which tells me that it in the dash somewhere. I tried pulling the signal and hazard flashers with no result, I've already tried disconnecting the gauge cluster with no result. I've switched out the headlight switch with no result. The stereo was yanked out at some point, so I am wondering if maybe the dash light lead to the stereo got returned to a ground somewhere?? Thats my next theory. Luckily the truck came with a full set of 1986 shop manuals ( the real ones) and a full set of wiring diagrams.

Any other ideas to check out?

[Russell]

There are three stereo wires from the power harness -- a grey wire, a yellow wire and a black wire.

The yellow one is an ignition power source which turns your stereo on when the key is in the back position, on position, and crank position. The grey one is dash lights, and the black one is ground.

I'd think that if the grey one was touching ground, it should blow the fuse, but I suppose it is possible that something similar to that may be happening...

[pdxmac]

Well, I checked out those wire, and that isn't the cause either. It dawned on me last night that I haven't yet fiddled with the turn signal switch/stalk yet.. that really the only thing left to try, so I'll probably do that this afternoon.