Batboard

My new truck is being built by GM as we speak. Should have it the end of January.

I have an extensive install planned for this truck, but I do have a question regarding installing a headlight flasher.

Anything specific install wise I should know besides setting it up for ground side switching?

i seem to remember a thread relating to late model GM vehicles need some sort of mod done to get a flash to work correctly.

Flasher is a Whelen UHF2150A

Also, anyone worked around the rear heat/ac duct work? I plan to drop the headliner completely, but just wondering how much room is up there .

You will need a standard positive switching unit. The headlights are negative AND positive switched. You will need to add a relay to feed power to the high beam side with the headlights in the 'off' postition. You will also need to backfeed B+ into the BCM as to not trip a code. There are several other things that will also need to be addressed to make this work. Without experience in GM PCM circuits, I would advise against trying to make all of these modifications, as a PCM will set you back a mere $2200.00 and a 'flash' programming if you smoke it.

Yes- it can be done.
No- it isn't the easiest thing to do and that's why you won't ever see it done often.

Hmm great, I wonder just how GM did that considering the fleet market for suburbans and trucks in emergency service. Flashing headlights is so basic. I wonder if someone makes a plug in flasher module designed for this application.

So, I guess my best bet at this point is to use hidden strobes in the headlamps themselves and save the wiring headache.

I have had success using a diode to prevent the power from feeding back to the ground side. I have heard horror stories about the BCM but have never personally experienced it. Not to say it isn't possible. I have one sitting in the shop that I just fixed up. I'll take a look to refresh my memory and post how it was done and what flasher I used.

I'd appreciate it, however this is basically my new child so I'm going to be very careful with it.

Any other install tips on this vehicle?

IT's not the ground side that you need to worry about. It's the "checksum" BCM lead that will cause problems. The ground side toggles through the dimmer/FTP switch. You will need to fabricate a new crossover harness into the OEM light connectors.

um, why does a light need to have a checksum???????

Arrive at GM dealer, my truck has a bad checksum in block 2035!