Chevy Truck Headlight Wiring ?

[ChiliPepperGarage]

A little while ago I posted about performance mods for my '99 Chevy 1500 or selling and getting a Vette. Well I got a Corvette but decided to keep the truck anyway because it is a good run around vehicle. In that thread RD said that the inmates here can answer pretty much any question anyone would have so here we go!

It gets really dark out here in the boonies and we have lots of deer and other night critters so good lighting is very helpful. I installed an LED bar and a couple driving lights. Wired the relay trigger up to the high beams so they go on and off with the high beams. There was a red and black wire going to the high beam bulb so I tapped into the red one figuring black is ground.

Turned on the high beams and all the lights came on. Great! Flipped it to low beam and my auxiliary lights stayed on. Grabbed my test light, pulled the connector off the bulb and got power to the red wire on high beam as suspected but it is hot when on low beam too. Then just out of curiosity, checked the black wire and got the same thing, power on high and low beam. WTF?

Why would both wires have power and why both on high and low beam. I've wired in auxiliary lights on many vehicles the same way with no problem. What the heck is the deal with the headlight wiring on this truck?

Now I could just wire them up to a separate switch on the dash but it is much easier to have them go on and off with the high beams.

 

[racetrash]

Possibly a ground issue, backfeeding..no ground, it's gota go somewhere.

 

[Shlbyntro]

Or the light could be switch to ground by an ecm. I'm not familiar with Chevy wiring specifically but your lights may be controlled by a computer and not necessarily directly by the switches on the controls. In this case, the switch is often on the ground side of an "always hot" circuit.

Hopefully some other inmates are more familiar with chevys and can give some insight on to your truck specifically. I'm a Ford guy!

If not, its test light time...

 

[mjc]

I am pretty sure that gm picks the ground with the relay. If you want high and low to come on the same time you put a diode between the high beam light out and the pick on the low relay. If diode is in backwards both will be on whenever lights are on.

 

[rivermobster]

Two things....

I'm certainly no Chevy expert, but I've never seen one with a black and red wire to the headlights. Normally the low beam is tan and the high beam is Lt green.

Can you post a pic of what you tapped into?

Second...

I'd like to see how the relay is wired.

 

[rivermobster]

https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/headlight-circuit-diagram-1

 

[ChiliPepperGarage]

Two things....

I'm certainly no Chevy expert, but I've never seen one with a black and red wire to the headlights. Normally the low beam is tan and the high beam is Lt green.

Can you post a pic of what you tapped into?

Second...

I'd like to see how the relay is wired.

Here's a photo. When I had the truck in the garage they looked black and red but now looks like purple and orange. I taped into the orange but they are both hot whether on high or low beam.

The relay is wired as follows:

30 - battery
85 - ground
86 - to high beam (relay trigger)
87 - to aux lights

 

[Shlbyntro]

Oh dude... please get rid of that scotch lock/scissor connector once you get the wiring figured out

 

[rrrr]

Oh dude... please get rid of that scotch lock/scissor connector once you get the wiring figured out

Those are properly called an insulation displacement connector. Now you know.

How many boat trailers have you had to rewire because they came that way from the manufacturer? They really do suck.

 

[mjc]

Those are properly called an insulation displacement connector. Now you know.

How many boat trailers have you had to rewire because they came that way from the manufacturer? They really do suck.

No shit I spent a lot of time rewiring with soldering and shrinking wrapping to fix it on one of mine

 

[rivermobster]

Here's a photo. When I had the truck in the garage they looked black and red but now looks like purple and orange. I taped into the orange but they are both hot whether on high or low beam.

The relay is wired as follows:

30 - battery
85 - ground
86 - to high beam (relay trigger)
87 - to aux lights

View attachment 772649

I'll look for a better wiring diagram when I get to work tomorrow.

 

[Shlbyntro]

Those are properly called an insulation displacement connector. Now you know.

How many boat trailers have you had to rewire because they came that way from the manufacturer? They really do suck.

Factory wiring from extreme and this is only a small portion of what I removed. I was severely disappointed

 

[Riodog]

Factory wiring from extreme and this is only a small portion of what I removed. I was severely disappointed View attachment 772793

No expert here, but when I put on my extra lights I just pulled the extra light module and everything seemed to work just fine,land i got rid of the driving lights also. The module i pulled was under the left kick panel on the drivers side. the dealer wouldn't do it for safety reasons.
Rio

 

[rrrr]

Factory wiring from extreme and this is only a small portion of what I removed. I was severely disappointed View attachment 772793

That's pathetic. The crimp connectors were mashed with a 99¢ tool from Hankow Freight. Extreme should know better, that's cheap, crappy product and execution.

This Greenlee rachet crimper is what I use. It's about $55 on Amazon. I also use Ancor crimp connectors with adhesive lined heat shrink.

Use both on boat or trailer wiring and it's a strong waterproof connection. Do it right, or do it over. It's not a difficult choice.

 

[ChiliPepperGarage]

Oh dude... please get rid of that scotch lock/scissor connector once you get the wiring figured out

Yes. All the wiring is temporary until I get it all working. Then I will rewire and secure everything properly.

 

[ChiliPepperGarage]

I'll look for a better wiring diagram when I get to work tomorrow.

Thanks!

 

[rivermobster]

Thanks!

Somehow I think you tapped into the fog light circuit. That's the only circuit that has the color wires you tapped into.

The high beam bulb is going to be lit up through the green wire.

Find the green wire and tap into it. That should give you the correct signal for pin 86 on your relay.

Make sure pin 30 on the relay is fused.

Once you have everything working, crimp all your connections with non insulated connectors, and then cover em all in marine heat shrink. Harbor Freight will have nice plastic boxes of the heat shrink you need. You want everything water proof.

Gimme a call if you need any more help!

 

[ka0tyk]

switched grounds. i ended up grounding all my lights so i could keep my regular beams on with my high beams and did the wiring mod with diodes, etc.

as far as brightness of the chevy, i ended up doing 50w led's... they're beyond bright. with 3 sets on (low, high, and fog) driving rice road it looks like stadium lighting. the bugs on my windshield love it.