four headlight truck?????low/high beams

[charlesg]

why do the low beams go out when I put the highbeams on????

 

[yevgenievich]

High side of low beam is burned out, or wrong lights or wrong wiring

 

[charlesg]

Thank you!

 

[yevgenievich]

If you have pictures of the wiring behind the lights it might help narrow it down

 

[charlesg]

New bulbs and still does it, this a normal gm thing??

 

[73c20jim]

attached wiring diagram.....I hope

 

[73c20jim]

Looks like either, not both.

 

[charlesg]

If you have pictures of the wiring behind the lights it might help narrow it down

The drivers side has two browns one black, ps one brown one black, highs have one green one black, can I do the 4 high mod on this?

 

[73c20jim]

I believe the reason the lows go out when the highs come on is that some states limit the amount of lights being on at the front of the car.

I would check with your state laws before you do any mods....or maybe like me you don't care. lol
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Blacks are grounds. Brown powers lo, green powers hi. They both go separately to the dimmer switch which selects one or the other.

That's how I interpret the wiring diagram.

 

[73c20jim]

What is the 4 hi mod. How is it wired.

 

[yevgenievich]

Yours seem to be split and not set up for four lights to be on. What year is it? The best way would probably to install relays to trigger from headlight switch and wire the lights to be on with high beam. But on regular 88 and earlier four headlight set up there is a green wire and brown wire connecting to low beam light. It lights up differently with high vs low

 

[Crispy]

You can do the 4 hi mod at the dimmer switch by jumping the tan wire to the yellow wire...

BUT

(big but)

You need to run relays to take the load off of the headlight and dimmer switches. Otherwise you will either blow a fuse, burn switches, melt a wire, or possibly worse.

Found this video online but its for an early GMT400

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[rpcraft]

FWIW the reason both lights do not stay on from the factory is because the wiring gauge is too small to support the current for a sustained amount of time and someone at GM never really considered that it was beneficial to have both on. Not sure why. The 4 hi mod includes a relay and thicker gauge wiring usually. There are kits you can buy online. I think LMC even has one that is priced fairly economically for what it is if you are not friendly with wiring.

 

[bucket]

On GM vehicles with the normal sized sealed beams, they are wired so all 4 lights come on with the brights. When they started switching to composite lamps, they went away from that. The mini-sealed beams must have been wired like the composite lamps. I've never owned one with the mini lamps.

 

[Battlac40]

You have to use camero parts and follow the scheme