1988 K5 headlight issues

[devlmaycry81]

Okay, so I've been trying to line out this 88 K5 I picked up about 6 months ago. Tons of issues from previous owners, 2016 l83 swap, 6l80e.

Hacked interior wiring, underhood was pretty messy, but headlight circuit didn't appear molested.

I'd gone through the normal stuff with replacing dead and missing bulbs, installing the front turns/running lights that were missing. Patching a busted wire at the tails, and cleaning grounds up.

The first issues I had with hi/lo beam were fixed with installing the passenger turn/run light bulb correctly. Socket was worn out enough it went in wrong and would stay bright with the headlights on and cause the passenger headlights to not work on hi-beam. Weird, but seems fixed now.

I've looked at the FSM for wiring, replaced the dimmer switch, did the relay mod (huge difference), got some cheap H4 housings that are glass, new bulbs, etc.

The only lingering issue is on the lo-beam top lights are bright and the hi-beams have a faint glow. When on dim I have 12v to tan and green. When I click over to high beams the bottoms go bright, like the top, and top ones (lo-beam) get dimmer, but still more bright than the hi-beam glow when on dim. With 12v to green only.

The first question is, is this normal behavior? I can't seem to find any videos showing normal operation, but what I can find shows all 4 being bright on hi-beam.

The second is, anyone have any idea what could be causing it? It seems the hi circuit shouldn't have 12v when on low, and outside of the dimmer the headlight switch shouldn't contribute to that behavior.

Kinda stumped and any help would be appreciated.

 

[Matt69olds]

Check the headlight grounds on both sides. Sounds like you have a poor connection, and the bulb that isn’t suppose to be on is supplying a ground instead of the actual ground wire.

 

[48hd]

THERE WAS ALSO A RECALL TO REPLACE THE HEADLIGHT SWITCH.
I GOT MINE DONE FREE. 1986 C-10

 

[48hd]

LOOKS LIKE IT ONLY APPLIED TO 1986 MODELS

 

[devlmaycry81]

Check the headlight grounds on both sides. Sounds like you have a poor connection, and the bulb that isn’t suppose to be on is supplying a ground instead of the actual ground wire.

Thanks for the info!

Prior to posting I'd already de-pinned the headlight connectors, wire-wheeled all of the ends, pulled the grounds on both sides, and wire-wheeled them and the rad support spots. The passenger ground is on the same spot as an engine ground and a relay ground for my e-fans. Could it sharing the same space be a contributor? Also checked continuity of all the wiring (due to the odd front turn signal behavior) to ensure it was correct. Def had some poor connections on the type 56 connectors due to corrosion initially.

The poor ground sounds like a simple enough explanation, and I can double-check them and also add/replace the grounds. I'll go ahead and move the passenger side ground to a different area as well to eliminate any X factors there.

 

[devlmaycry81]

THERE WAS ALSO A RECALL TO REPLACE THE HEADLIGHT SWITCH.
I GOT MINE DONE FREE. 1986

At least the headlight switches are cheap. Might merit replacing if the other suggestion doesn't resolve the issue.

 

[Craig 85]

I had some issues on my '85 when I installed Hella H4/H1 headlights. Hella provides a short harness to connect to the H4 bulb. I had also added one of the high load headlight harnesses I found on Amazon. I had a problem similar to yours, but I can't recall the specific's now.

I know I ended up deleted the short Hella harness and re-pinned the OEM headlight plug and the new headlight harness. I obviously had something connected wrong because when I hooked everything up again, it all worked.

FYI when the high beams are on, all 4 lights should be on (high for the low beams).

 

[devlmaycry81]

I had some issues on my '85 when I installed Hella H4/H1 headlights. Hella provides a short harness to connect to the H4 bulb. I had also added one of the high load headlight harnesses I found on Amazon. I had a problem similar to yours, but I can't recall the specific's now.

I know I ended up deleted the short Hella harness and re-pinned the OEM headlight plug and the new headlight harness. I obviously had something connected wrong because when I hooked everything up again, it all worked.

FYI when the high beams are on, all 4 lights should be on (high for the low beams).

Thanks for the info! My lights def do not operate that way currently.

It's still on the factory harness, but I can see where it looks to have been altered in the past. There were several spots of splices that have crimp and solder connectors and what looked like black duct tape wrapped around them. Which may be stock, but the tape choice did not seem like a factory choice. The last time I worked on a square body was my old 81 c10 short bed and I haven't owned that truck in about 20 years now.

But, everything seemed to be wired correctly and had good continuity. Though I've yet to check the length from where it comes out of the wire cover back to the firewall to see if there are any issues there. Unfortunately, I haven't been able to get off work on time to be able to get out there and look at it before it's too dark.

 

[Craig 85]

When you pulled the pins to clean them did you move the pins to match the H4 bulb? I believe the ground and high beam are in different locations for the H4.

It's been over a year so I can't remember if I'm giving the correct info, but I do know they are different and that is why Hella gave the adapter.

 

[WP29P4A]

I have been working on electrical on my clients jeep rock crawler for the last couple weeks, one of the tasks was to replace the stock (properly working) headlights with LED bulbs. I installed the first one and it worked, but seemed a little dim. When I plugged in the second one the first one got brighter which was an immediate red flag. Lights NEVER get brighter when you connect more of them. I also had issues with high and low beams not acting correctly. I pulled out my test probe to verify pin configuration and found a ground swapped with one of the power wires at the headlight plug.

The original bulbs worked because they are not polarity sensitive like LED bulbs are. One misplaced ground created several odd problems that were easily corrected just by correcting pin placement.

Hopping this might help understand how a simple incorrect pin placement can cause such unusual problems.

 

[Ontheboulder]

Okay, so I've been trying to line out this 88 K5 I picked up about 6 months ago. Tons of issues from previous owners, 2016 l83 swap, 6l80e.

Hacked interior wiring, underhood was pretty messy, but headlight circuit didn't appear molested.

I'd gone through the normal stuff with replacing dead and missing bulbs, installing the front turns/running lights that were missing. Patching a busted wire at the tails, and cleaning grounds up.

The first issues I had with hi/lo beam were fixed with installing the passenger turn/run light bulb correctly. Socket was worn out enough it went in wrong and would stay bright with the headlights on and cause the passenger headlights to not work on hi-beam. Weird, but seems fixed now.

I've looked at the FSM for wiring, replaced the dimmer switch, did the relay mod (huge difference), got some cheap H4 housings that are glass, new bulbs, etc.

The only lingering issue is on the lo-beam top lights are bright and the hi-beams have a faint glow. When on dim I have 12v to tan and green. When I click over to high beams the bottoms go bright, like the top, and top ones (lo-beam) get dimmer, but still more bright than the hi-beam glow when on dim. With 12v to green only.

The first question is, is this normal behavior? I can't seem to find any videos showing normal operation, but what I can find shows all 4 being bright on hi-beam.

The second is, anyone have any idea what could be causing it? It seems the hi circuit shouldn't have 12v when on low, and outside of the dimmer the headlight switch shouldn't contribute to that behavior.

Kinda stumped and any help would be appreciated.

I went to an H4 bulb setup on my 87, had to swap the ground and low beam wires in the connector,just changed their position in the connector works great!! hope this helps

 

[Ontheboulder]

When you pulled the pins to clean them did you move the pins to match the H4 bulb? I believe the ground and high beam are in different locations for the H4.

It's been over a year so I can't remember if I'm giving the correct info, but I do know they are different and that is why Hella gave the adapter.

on mine it was the ground an the low beam, Octane lighting is the housings I got

 

[Rusty Nail]

Thanks for the info!

Prior to posting I'd already de-pinned the headlight connectors, wire-wheeled all of the ends, pulled the grounds on both sides, and wire-wheeled them and the rad support spots. The passenger ground is on the same spot as an engine ground and a relay ground for my e-fans. Could it sharing the same space be a

Yes.
Let's stop there. Gotta fix that first - or the rest of your efforts are in vain.

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