How do i fix electrical problem on my gmc?

THE CAR HAS LIKE 50+ ELECTRICS DEVICES,
ONE IS HEAD LAMPS THAT WORK KEY OFF DO THEY
IF NOT FIX DEAD HEAD LAMPS FIRST. FUSES.
IS STATER MOTOR DEAD
IS ENGINE DEAD
IS TRANSMISSION DEAD (ENGINE RUNS)
DOES DASH HEATER BLOWER WORK
DOME LIGHTS DEAD?
BRAKE LAMPS DEAD
TURNS DEAD
PARK LAMPS FRONT AND REAR AND SIDES DEAD/.
SEE, HOW COMPLEX 12DC POWER IS? AND MORE LOTS MORE. EVEN A DEAD RADIO

Headlight ground is a common problem. Also, check that the battery ground is sound, if battery ground goes to engine, check that engine strap to frame is also sound.

The turn signals and brake lights are on a different circuit from the parking lights. Did you check to see if you have power coming out of the headlight switch for the parking light circuit ?

I've got the same problem on 98 GMC Sierra.

I'm an electrical engineer, I checked the electrical diagrams and verified that there is no problem in the rear lamp assembly or wiring. With the light assembly unplugged, I can actually watch the blinker and brake signals operate with a voltmeter. The Tail light works OK.

It simply won't provide enough current to light the bulbs.

I'm afraid that it's melted one of a pair of normally closed contacts inside the blinker switch that feed the brake and turn separately on each side.

Disconnect the trailer wiring and recheck the vehicle lighting. If it returns to normal, then obviously the trailer is the problem. Quite often the trailer plug loses its independent ground and it will back feed thru other circuits trying to locate one. Especially if its a boat trailer, water intrusion can cause havoc on the grounds due to corrosion. The under hood electrical center has circuits intentionally meant to be used for trailers. You CANNOT just jumper into the rear lights of the truck (tail, signals and brakes coming from the tail light connector). Because it uses a multi-function switch, the brakes and signals are actually the same circuit, and have to be wired separately for a trailer plug to operate.

Put you a couple of more body grounds on it if that helps From the Block to the fender and from the frame to the body

most electrical problems are caused by bad grounds, get a dvom( digital volt ohm meter) and check continuity on your tailight and headlight wiring

Does your high mount stop light work? If it doesn't, then it'll be the brake switch located just above your brake pedal.

If the light does work, then it should be the electronic flasher module that will be located under your dash near the steering column. It will be labeled. This controls your signals, but I believe your brake lights are also on the same bulb as your signals, so when this goes, it can affect your brake lights

brake lights and turn signals work off the same curcit, it could be the fuse or the brake light switch !!!!!!