Hello everyone.

First things first; 87 Iroc-Z, 5-speed, Factory radio (non-functional at the moment, clock comes on albeit being wrong all the time)

Here's an issue I've had going for a while. All lights die after a while when I'm driving with high-beams on. The breaker in the headlight switch pops and the headlights + interior lights (lights in intrument cluster, probably radio and AC-controls too) dies. Comes back on when it's cooled down.

It only happens with the high-beams on, but I can feel the switch getting hot when I lay my hand on the section of the dash it's housed in, even with the high-beams off.

I've replaced the switch in the steering coloumn and the dimmer switch in the dash (gauge dimmer was not working). Looked at & cleaned the grounds I could think of (how many are there anyway and where?) , same with the contacts on the headlights themselves.

What else could it be? I was wondering if the printed circuit in the back of the instrument cluster could be part of the problem as it has some corrosion and it's old? I had to clean some tracings to the SES-light to get it functioning again and it got me thinking about just that.

Could the high beams be drawing too much current because they might be old?

Fuses were okay when testing with a light, but I'm thinking of replacing them anyway. Hoping for some good answers that can lead me in the right direction.

Thanks!

 

You can buy a cheap inductive amp clamp off Amazon and check individual high beam bulbs for draw. Ground would absolutely be my first assumption, but with the wiring in the car being almost 40 years old, anything is possible

 

That's not a bad idea. And do you have any pointers to what grounds I should check out & where they are located?

 

"Grounds" can't really cause that.

Ground in effect is the opposite side of the power circuit. Power flows from the batt, through the switches, through all the various wiring, through the bulbs, to ground, and back to the batt via the neg cable. All that a "ground" problem would do, is make the lights dim or intermittent, the same as a bad connection anywhere in the 12V side would do. A bad "ground" CANNOT cause excessive current to flow through the switch(es).

More likely, is that a wire is pinched or chafed somewhere. An EXTRA "ground" CAN cause excessive current to flow; butt it would be an UNINTENTIONAL one, not one of the ones that's supposed to be there being bad somehow. Aka a "short".

Good place to start would be by disconnecting the wiring at different points in the circuit, as convenience allows; and measuring the current flowing through the switch(es). C100, the big bulkhead connector below the brake booster, is in 2 halves; 1 half has the batt feeds into the car and all the engine-related stuff (gauges, ignition, etc.), and the other has all the body-related stuff in it (front lights, horn). The HL sw also feeds the tail lights, which are fed by a completely different route, namely the "Fisher body" connector which is under the carpet about directly below where a clutch pedal would be; and a few other things in the car, such as dash lights. Which incidentally, do THOSE work right? Do they dim properly and everything? If they DON'T, like if they only work with the dash dimmer turned to full bright and then go completely out when you dim them, then you have a dash light circuit problem, which the first place I'd look for that, would be the radio wiring. Especially if that's been hacked on as is nearly always the case.

First thing I'd do is set up to measure current from the batt, like you'd do for a parasitic; turn on the headlights and see what the current is; then start disconnecting those connectors, and the dimmer sw, to see where the current is going. First connector I'd check would be the "Fisher body" one. With the headlights on you should see maybe 25 - 30 amps coming off the batt. Should be maybe 5 - 10 amps higher with the high beams than the low. Change to the parking lights, you should see only 5 amps or so off the batt. Then disconnecting the FB connector should drop that by about half. If the current starts out higher than 30 with the HLs on and higher than 10 or so w just parking lights, and disconnecting the FB connector drops it by ALOT, then the problem is toward the tail lights. If on the other hand the current stays high, the TL wiring is OK; plug that back in, and unplug the dimmer sw next; the current off the batt should drop to 5 amps or less and of course the HLs should stop working both in low or high beam. If that's OK then you can eliminate the wiring in the dash and around the HL sw. Then unplug the half of C100 that feeds the body; the current should drop to just a few amps (tail lights only). And so on. Eventually you should find that there's WAY TOO MUCH current going somewhere, and be able to identify which branch of the car's wiring the problem is in.

Use logic. Works EVERY TIME. Especially on something as dirtball simple as car light wiring, which is the simplest part of the simplest kind of wiring (automotive) that there is. It's just not that hard if you climb out of "maybe it's this maybe it's that" hell and USE LOGIC instead.

 

If you have aftermarket headlights,..... remove them and re-install factory parts. I've found that several aftermarket headlights are wired different to the factory and people that don't know this hook them up as the factory did and this burns out the High Beam switch &/or the Headlight switch.

If the radio isn't working then I would unplug it. The BROWN wire at the radio plug is the headlight ON signal wire and since there is a known problem with the radio then I would remove it from the wiring harness to eliminate the chance that it could be causing problems on the Headlight ON signal circuit.

You *might* also have a failing Fusible Link "A" at the starter. Works under moderate load,.. but when HIGH BEAMS require a heavy load it's too much for the fusible link. The only other things that fusible link "A" powers other than the Headlight Switch (according to the 87 power distribution diagrams) that is not seen on the diagram below is that it feeds the TAIL LIGHT fuse and the Fog Light Relay.

 

I would tend to discount the possibility of a fusible link being the root cause of this behavior. Keeping in mind, that a FL is merely a piece of wire, that MELTS ("fuses") when overloaded. They can have other failures as well; most notably, a bad connection where they're crimped to the wires they protect; butt some LOGIC will help illuminate the likelihood of one causing the issue at hand.
.

1. A failing fusible link won't make the headlight switch get hot.
2. A failing fusible link, when it opens, takes out about half of the car, not merely only the stuff that depends on the HL sw.
3. A failing fusible link rarely repairs itself predictably and reliably after failure by simply cooling back down, goes back to normal (with all the other stuff that it supplies power to ALSO working normally), then fails AGAIN in the EXACT same way later on. Repeatedly.

Note that I am NOT saying "your FLs are good; NOT saying "don't bother looking at your FLs"; NOT saying ANYTHING of the kind. NOT NOT NOT NOT NOT NOT NOT. Please do not put any such words into my mouth (keyboard). There very well may be a problem with FLs, and of course, they are well and widely known by all, myself included, to be a major suspect in electrical system problems. However, since they CANNOT account for ALL the symptoms that are OBSERVED, they also CANNOT be the cause of this issue. It is just about as likely as blaming it on alien abduction and the aliens are just wanting to test to see how stuuuuupid these miserable carbon units really are by stumping some random one of them with ... this. Yeah, ... ,,, ... NO.

See my signature for a helpful mental tool useful in troubleshooting. EVERY SINGLE WORD is important; in this case, "fits all the facts" with emphasis on ALL, should be the guiding principle.

Use logic. Always. At all times. In all ways. ONLY. No "maybe it's this maybe it's that". Do not depart from the path of LOGIC.

Troubleshoot by disconnecting things until you find the direction toward which the symptoms lead to the problem. It's BY FAR the easiest way of locating and zeroing in on a problem of this nature. Speaking strictly as a long-time former broadcast engineer who frequently had to troubleshoot and repair high-power radio & TV transmitters, and usually, this was the ONLY way to find a fault within them.

 

I knew I did the right thing when deciding to post here instead of some group on Facebook.Would've just gotten suggestions about doing an LS swap or something... I haven't chuckled this hard in a long while. Great tips and suggestions here, really appreciate it you guys. Thank you, sincerely.

Forgot to mention that the headlight switch was replaced due to the dimmer being broken, felt it was very off and felt wrong when turning the kno...uh.. tiny wheel. The dash didn't dim down either, lights were only on (with full brightness at that) when the button was turned to the max. It got replaced with a unit off Rock Auto, that fixed it.

No aftermarket stuff here, unless Wagner lamps are aftermarket...? I haven't done diddly squat with them, so I dunno if they are stock or oem replacement.

This stupid carbon unit is going to make a game-plan and attack this alien-issued electric boogaloo when I get home from sea. It might take a while, but I promise you I'll return with what I'll might find. Coffee makes brain work gooder. I do have the Gm shop manual & electric supplement to read through as well.

 

If you've got factory style Headlights and no aftermarket stuff your good to go there ! I've had to replace a couple melted/burnt High Beam switches after guys installed aftermarket headlights because they wired them up the same as factory when the terminals on the lights are different. Knowing that,...... my fist check would be the Fog Lights / Fog Light Relay.

While it's not shown on the schematic I posted; the Lt GREEN wire that connects to factory splice 'S150' (NOTE "R") is the High Beam signal wire to the Fog Relay. Fog Lights should not work when the High Beams are active. It's POSSIBLE that ( if the car had ) a previous owner modified the wiring to allow the High Beams to become active when Head OR Beams are active, or it could also just be a bad relay. If your sure the High Beams are what is triggering the issue than something connected/related to the High Beam circuit is almost certainly causing the issue. To START checking into this problem with the least amount of time and effort,....... I'd unplug the fog light relay from the headlight harness ( 2-wire connector near fog relay ) and then drive the car for awhile when using the High Beams and see what happens.

Good Luck !!

 

Uhh guys...? Why does my fuel pump prime when I'm activating the hi-beams?

 

You have a short.

 

Alright, so..Could this be the very reason why the headlight switch overheats & then cuts off all the lights when hi-beam is activated? If the fuelpump is in a magically and sadistical way is somehow connected/effed to the light-circuit then I reckon it's a heavy load on that 'lil switch.

 

I disconnected the high-beam lamps. The fuel-pump stopped priming when I only run the outer lamps in high-beam mode.

 

Also, it made no difference whether the fog light relay was connected or not.
My day is somehow ruined and I'm hungry. Gonna call it a night. What could I try to do to fix this tomorrow?

 

You absolutely have some type of "cross short" going on there, be it from natural causes or man made. One example of natural causes could be that a wire in a harness somewhere got so hot that it melted not only it's own insulation, but also the insulation of adjacent wires and now some of those wires are in actual contact with each other. Man made causes could be if someone with more wirecutters than brains has been at the wires, and pulled the ol "This wire has power in it, I'll just run it over to here where I don't have power, and my problem will magically go away". I'm wondering if somehow someone futzed up and wired the high beams into the fuel pump relay somehow......

But, now I gotta ask ya, does the fuel pump run without the high beams on? cause if it does, if without the high beams on your still able to start and run the engine, that would mean the pump should still be getting power from it's normal source of power, as well as getting power when you turn the high beams on. If that is the case, it may well not be the fuel pump itself that's causing all of the headlight switch heating & such, and leaves me wondering if anything else is getting power from the high beams as well.

Gotta admit, in my years here trying to help people with their electrical gremlins, your the very first whose ever presented a "my high beams run the fuel pump" situation, , , , , so there, now don't ya feel special? .........

 

Hiya Orangebird! Welcome to the party!
Yessir, when I disconnected the hi-beams the fuelpump still primed as usual when using the ignition-sticks.

I came across an old thread here;

https://www.thirdgen.org/forums/elec...fuel-pump.html

After reading this thread I tried disconnecting the 2-wire connector from the ignition-coil. And lo & behold, headlight's does not prime FP.

 

Also; I uhh...Don't want to feel special, special is bad. Special means that it's maybe not an easy fix. Heheeeh, darnit.

 

Alright. The fog lights and turning the blower motor on the highest setting also primes the pump. The plot thickens. Gosh darn it.

 

KOHV94, I hate like Hell to have to post this, cause I really do respect your sense of humor here, but.....

And this is a really BIG butt...

I do believe you've got one of three things going on here, a wire fire having caused a cross shot, someone connecting wires where they shouldn't have, or perhaps some weird grounding issue.

Sadly, I believe it's gonna take someone with extreme car electrical chops to actually lay hands (and voltmeter) on this car for this to be solved. I do not believe this is something I could ever diagnose over the internet without actually being able to see the car. My only best suggestion to you here is that if you are at all versed in car electrical work get a real FSM (field service manual) covering the wiring (NOT "Chiltons" , Haynes" or any other of those glorified owner's manuals, a real deal GM FSM covering your car) and begin examining your wiring VS what the manual shows to try to find where your car's electrons are going astray.

You have my utmost apology that I can't be of any further help to you here......

 

Thanks for that OrangeBird. I appreciate your insight, I really do. Alright, made some new discoveries here.
When I disconnect the 4-pin connector to the distributor all the issues goes away.

I am currectly in the process of trying to replace one of the coolant hoses for the heater core (the one that goes doen along the firewall), which means that I'm also going to fiddle with the wiring down behind the distributor. I am going to look at the wiring after getting them out of the looms to see if I find any damages to them.

I'll also mention that apparantly the foglights priming the FP seems intermittent, as when I came back to the car today and tried "stuff" before getting to work they didn't prime the FP. Cleaned the contacts for the plug & relay and then they started doing it again.

I do have the GM workshop manual and electrical supplement for this car & it's year.