electrical help, headlights and brake lights only

[muddybuddy]

hey guys, my '88 k5 randomly started having electrical issues with the lights. the headlights and brake lights work, but the turnsignals and tail lights dont work, neither do my gauge lights. i already replaced the switch, but that didnt help anything. i hate electrical stuff and it seems like such a pain in the arse to try to track down some short and theres no guarantee that i'll even find it. if i replaced the entire light wiring harness would that solve my issue?

what are my options? thanks guys, help the electrical noob

 

[Muddytazz]

Start with the easiest possibles first, check your fuses and your grounds.

 

[K85 Octane]

ugg

Not working:
blinkers
rear running lights (the larger bulbs)
entire dash lights

Working:
headlights
all running lights
brake lights
dome light?

What switch was replaced? The knob or...?

 

[muddybuddy]

headlights and brake lights are the only ones working. the turnsignals, running lights dash lights arent working. i replaced the headlight switch that the knob attaches too with no luck, wishful thinking that it would be that easy, but it never is haha

 

[muddybuddy]

Start with the easiest possibles first, check your fuses and your grounds.

i checked the fuses and they are looked good. where abouts are the grounds for the lights? stock location, nothing has been altered with

 

[K85 Octane]

most everything shares it's ground with something else. On the core support is where all the front lights are grounded. Behind the tail lights is where all the rear stuff is grounded.

You have a few different things not working, and it seems like all are separate.

Dash lights = fuse, ground behind the gauge holder on left side, bulbs, wire, wire coming from light switch, bad contact with printed circuit

Blinkers = bad ground (but they share a common ground I think) bad wire coming from blinker cam in column, bad fuse, bad blinker "blinker" thing on fuse panel,

Running lights = light switch, the wire coming from the light switch. The running lights are simple. Power goes into switch, power goes out to running lights. But some running lights are also blinkers. In the rear, you have running lights, brake lights, and blinkers. All three use different bulbs except one, it shares blinker/ brake light duty. Ugg, thinking...... the little 168 (I think) also shares blinker/ running light duty. UGGG I put this crap behind me lol

Ugg, I just rewired my whole truck and most of it I sh1t canned. Brain so fuzzy

 

[K85 Octane]

question for you

when did this happen?
Happen one at a time or all at once?
recent mods that took place just before lights taking a crap
any tall brush you drove through lately LOL, wires running along driver's side frame rail. Everything but pink has to do with lights. Do you have the trailer harness thing on the back? Ugg, but brake lights work. hmmmm

 

[muddybuddy]

it just happened out of nowhere, pretty sure the truck had just been sitting haha. its so frustrating. it does have some kind of trailer lights in the back. i havent touched any of the lights recently it just randomly went out.

in my searching i read that the dash lights wont work when the tail lights dont work so that you know something isnt right. i was under the impression that all my problems are linked to one thing, some sort of short or something

 

[Chaddy]

Bad bulbs?

 

[K85 Octane]

the gauge blinker bulbs act funny, but the rest of the gauges should still work.

The headlights, dash lights, and running lights all run through the switch. The dash lights have a ground behind the bezel on the left. All the exterior lights are grounded near the light itself. (front stuff off core support, back lights I think are behind tail light)

lol, did u check any bulbs yet?
might be all on strike at once

 

[4X4HIGH]

it just happened out of nowhere, pretty sure the truck had just been sitting haha. its so frustrating. it does have some kind of trailer lights in the back. i havent touched any of the lights recently it just randomly went out.

in my searching i read that the dash lights wont work when the tail lights dont work so that you know something isnt right. i was under the impression that all my problems are linked to one thing, some sort of short or something

Most problems like this can be attributed to the usually hacked trailer wiring. Start looking (even better temporarily disable) the trailer wiring.

 

[Fordum]

OK, first of all, hit your emergency flashers. Do all four bulbs flash?
If the front ones don't flash, check the front bulbs. The rear bulbs are good, since the brake lights work. But blown front bulbs would stop the turn signals.

If all four bulbs flash then I suspect the turn signal switch.

BUT, if the indicator lights on the dash just glow when you turn on the turn signals, or if they glow when the headlights are on, let us know before you replace the switch.

The power for the dash lights comes from the rheostat on the light switch.
I assume that you have turned the knob all the way over to make sure the dash lights are at maximum brightness?

 

[4X4HIGH]

He's already replaced the switch and gets the same thing.

 

[Fordum]

I may have misunderstood.
I thought he had only replaced the headlight switch, which was why I asked about turning the knob since the new one might have had the dash light brightness turned all the way down out of the box.

If he has replaced the turn signal switch, i missed it.

 

[4X4HIGH]

My bad, I thought you were saying to replace the headlight switch, which he already did.

I can tell you from a past experience I had that a bad bulb can play all kinds of games by back feeding power where it shouldn't be. Quick story about my issue, years ago I had a 66 Chevy II and everything worked fine until one day when I was driving at night and I hot the brakes and the dome light came on, the dash lights went off, and the radio stopped playing. I chased this for a bit before discovering a burnt taillight bulb. I found it so hard to believe that after swapping in a new bulb and the problem went away that I install the bad bulb again just to have the same symptoms reappear.

I also had another situation with a 70 Chevy truck I owned and that had a bad ground strap from the engine to frame (can't remember the exaxct details on that one but once again I couldn't believe it and swapped the "bad" strap back in to have the problem reappear again). Mind you that the "bad" strap looked like new still.

Can't stress enough GROUNDS GROUNDS GROUNDS, they are the DEVIL when it comes to electrical issues.

 

[Fordum]

Man, you are preaching to the choir about grounds here. Not only have I run into all kinds of stuff with car grounds, but I live and do electronics work in lightning country.

I millohm difference between two grounds can result in several thousand volts difference.

And what worse, is split grounds. Like when the phone company does not hook their ground to the main house ground.
A close lightning strike will charge up the ground. When the charge gets to either the phone or electrical ground before the other, you suddenly have many thousands of volts difference looking for the easiest path.

Answering machines are plugged into both the ac line and the phone line........Bye Bye answering machine.

And then I get called in to work on boats......

It took three of us to tow in a boat whose rudder just fell off due to electrolysis.

And, I know what you mean about putting the bad stuff back on. Sometimes you just gotta try......

One of my worst ground car problems:

I was helping trouble shoot a car that had had multiple in-tank pump failures.
My friend called me. She had brought it in, and told him that another shop had replaced the pump 3 times in a month.

Problem was, the latest pump seemed to be bad too.

He did not want to be the next guy to replace one and have it come back.
When I got there, he had just replaced it, and it was working.

He had bypassed the relay so it would keep running, and was standing under the car.
He asked if that pump sounded normal to me. It didn't.

I measured the voltage going to it and it was fine. But, the current was too high.
Just for fun, I measured the voltage from the hot wire to the pump to the ground wire to the pump.

Low voltage.
I grabbed a piece of wire, hooked it to the neg term of the battery and touched it to the pump ground.

The pump sped up, and suddenly we started hearing a dinging noise from inside the car.

We started following that ground wire.
It went up behind the passenger side rear seat back, across under the deck below the back glass, where it supplied the ground for the rear window defroster, down behind the back of the driver side rear seat, under the rear rocker panel, under the front rocker panel and hooked into a massive ground system which was all corroded due to water getting into the panel.

When we fixed that ground, her radio worked again, the drivers side window worked, the key dinger worked, and no telling what else.

He charged her only the normal labor for replacing the pump, despite the fact we spent an hour tearing the car apart and putting it back together again.

She cussed him out for charging her for working on the radio, window, and I think the fan.
He showed her where he did not charge her for any of that, and in fact had charged her less to replace the pump than the other guys.

She told him that she had not authorized him to work on that other stuff, and she was thinking about filing a complaint.

I was headed toward her car with screwdriver and wire cutters. I was going to cut all the grounds back loose except for the fuel pump when he stopped me.

He told her to go ahead and file the complaint. Just to make sure to never come back to his shop again.

I was hoping she would file, but she didn't.
Sure enough though, when the other shop screwed up another electrical problem about 6 months later, she was back.

Didn't get any service though....

 

[muddybuddy]

OK, first of all, hit your emergency flashers. Do all four bulbs flash?
If the front ones don't flash, check the front bulbs. The rear bulbs are good, since the brake lights work. But blown front bulbs would stop the turn signals.

If all four bulbs flash then I suspect the turn signal switch.

BUT, if the indicator lights on the dash just glow when you turn on the turn signals, or if they glow when the headlights are on, let us know before you replace the switch.

The power for the dash lights comes from the rheostat on the light switch.
I assume that you have turned the knob all the way over to make sure the dash lights are at maximum brightness?

the indicator lights dont turn on at all. i did turn the knob all the way both ways on the headlight switch to make sure the gauge bulbs werent dimmed out. i havent messed with the turn signal switch, but that would mess up the running lights?

i never use the trailer lights for anything, i'd love to get rid of the harness that is just sitting back there. how do i go about getting rid of that?

thanks for the help guys! sounds like i'll have to checks the grounds for sure

 

[mudbuggy]

You have never used the trailer pigtail? Might just be a corroded wire in that section prematurely grounding and with voltage going the path of least resistance, instead of going to the lights, its just going to the damaged area. Would you happen to have stuffed the trailer harness up on the frame rail or wire tie it to a crossmember? I'm guilty of doing that before and felt lika a fool when I basically caused the problem!

 

[Fordum]

To get rid of the trailer harness, depends on how it is hooked up.

They probably just spliced into the wire harness in the back.
You can just get up under and remove the wires going to the trailer harness.

If you are really lucky, they used an adapter. Your left and right rear lights have a connector in the middle where they split off.
Its behind the bumper, in the frame channel about midway from side to side.
Just follow the wires.

There is an adapter made that you unplug the splitter and plug this in between.
If you have one of those, all the trailer wires will go to a plug.

Just unplug both sides from that plug and plug each half to each other and you are in business.

Assuming that does not fix it, we need a little more detail.
First, try the flashers, of course, then, do the front running lights, also called parking lights, come on when you turn the headlight switch to park?

I am looking at a schematic, and trying to figure out where a break would have to be.

Do you have a voltmeter or test light? We can tell you how to use one if you do.

I'm going to post a couple of schematics here. Don't worry, we know what they mean, and we can show you anything you need to know, as long as you have them in front of you to reference them as we talk you though them.