03 Chevy Suburban k2500 4x4 3/4ton upcoming install

apco25 · Post by **apco25** » Mon Dec 30, 2002 12:51 pm

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 .

jim · Post by **jim** » Mon Dec 30, 2002 2:42 pm

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.

apco25 · Post by **apco25** » Mon Dec 30, 2002 3:48 pm

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.

fire-medic8104 · Post by **fire-medic8104** » Mon Dec 30, 2002 6:06 pm

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.

apco25 · Post by **apco25** » Mon Dec 30, 2002 8:36 pm

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?

jim · Post by **jim** » Mon Dec 30, 2002 8:40 pm

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.

apco25 · Post by **apco25** » Mon Dec 30, 2002 8:45 pm

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

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