So from what I gathered my truck has a ground-side switched headlight system according to Galls and it requires "Modification 3". When I got my S-10 it had automatic headlights and daytime running lights. To disable the DRL I had to cut a wire going to a relay under the carpet on the driver side and to disable the AHL I had to put a resistor in the light sensor on the dash. This enabled me to fully control my headlights with the factory switch that was seemingly useless because the headlights stayed on all the time no matter what position you put the switch in. So with these modifications I'm not sure how to follow the instructions given with any headlight flasher. Specifically I want to use the Whelen UHF2150 because it flashes the high beams while still having the functionality of the low beams. In the instructions it says it will "alternately flash the high beam headlights on any vehicle with a 12 volt D.C. negative (-) ground electrical system" however these two websites I found it for sale on, Fox Public Safety Equipment and Big Country Supply, say it is for vehicles with a positive switched electrical system. So which is it?