Electrical Engineer Needed - 99 Silverado 1500 Headlight Issue

[Neal Hardin]

Firstly, i did a search and nothing.  I have pulled out all of the stock ECU/TCU (running a TH-400 now) and replaced with Holley Terminator X.  The Fuse box is still there with all the parking lights, turn signals, windows, radio, fan, etc all WORKING...but when I turn on the Headlights, NADA!  I have checked the Switch (all good), Fuses (all good), Relays (working) and nothing. 

 

We tested the headlight plugs and they are not getting power.  I have all new grounds on the motor/chassis and Someone told me to check the "dome light" and turn on/off a 1000x and NADA.  It's in the garage, and same person asked me to check the "light sensor" on the dash, and that the dome light works that too.  i have NOT replaced the multi-switch for the turn signals/high/low beams, as they were all working before I deleted the ECU and wires.

 

I made a Video here:

 

Thanks all!!

 

-Neal

[Jsdirt]

I have minimal time, so I couldn't watch the vid - just FYI.

 

Everything on these is controlled by the BCM (Body Control Module). Switches are just inputs to the BCM - they don't actually switch current going to the lights. The BCM makes the electrical connection to the lights.

 

You're going to have to wire them in old school, but you'll have to use a cube relay to run the lights, since the switches are so crappy they'll fry to a cinder the moment you turn the high beams on. Actually, it'd probably fry on low beam. They were low bidder designs to start with, and NEVER designed to carry the actual load of the lights. Be prepared for all kinds of strange backfeeding to the cluster, too, like the high beam light staying on at all times, dimly. I would scrap that and install a complete custom cluster, either using Autometer or high end digital gauge packages that are out there.

 

So, throw the BCM in the trash, and wire them up with a relay. The BCM controls many other things as well, so you're going to be doing a LOT of wiring. Normally EVERYTHING goes through the BCM - wipers, HVAC, windows, locks, and key security for a crank, and run signal. It'll be a bit of a PITA, but you'll have the most reliable '99 out there when it's all done.

Edited October 11, 2023 by Jsdirt

[Neal Hardin]

On 10/10/2023 at 10:58 PM, Jsdirt said:

I have minimal time, so I couldn't watch the vid - just FYI.

 

Everything on these is controlled by the BCM (Body Control Module). Switches are just inputs to the BCM - they don't actually switch current going to the lights. The BCM makes the electrical connection to the lights.

 

You're going to have to wire them in old school, but you'll have to use a cube relay to run the lights, since the switches are so crappy they'll fry to a cinder the moment you turn the high beams on. Actually, it'd probably fry on low beam. They were low bidder designs to start with, and NEVER designed to carry the actual load of the lights. Be prepared for all kinds of strange backfeeding to the cluster, too, like the high beam light staying on at all times, dimly. I would scrap that and install a complete custom cluster, either using Autometer or high end digital gauge packages that are out there.

 

So, throw the BCM in the trash, and wire them up with a relay. The BCM controls many other things as well, so you're going to be doing a LOT of wiring. Normally EVERYTHING goes through the BCM - wipers, HVAC, windows, locks, and key security for a crank, and run signal. It'll be a bit of a PITA, but you'll have the most reliable '99 out there when it's all done.

Thank you...that is what I was afraid of.  I have a Leash Electronics Street-Strip board that I was going to hook up.  I will mess with this BCM a bit more and will just learn on it now.  Ultimately, I will rip-n-replace.  Appreciate the help!