My 1998 chevy 4x4 brake lights work fine with the key off but when you turn the ignition on the brake lights go off

What have you checked so far? How old is the Remote Starter? Is this a factory unit or aftermarket? If aftermarket, what is it? How well does the truck start with the key in the ignition? If the truck starts fine with key, do me a favor. Sit inside the truck and close the door. Do not touch the brake pedal during this test. Stick the ignition key into the ignition and leave it there (don't turn it). With the key in the, activate the Remote start. Did the engine start or did the engine crank but not start (very different reasons)? If the engine did start then the issue is related to the Security System. If the truck did not start you will need to take a closer look at things that will prevent the autostar system from operating. A signal from an open hood, open door, interior light or brake light will cancel the remote start command. Please let me know how you made out and what you found. Good luck.

I would try measuring for 12 volts at the socket while the turn signal is on.

Could be the ignition switch itself. Under the hood where all the wires go into the fusebox in the cab is a good pkace to start. You need to take the bolt/nut off and pull the box and wires apart. I have seen fuse blocks heavily corroded and cause problems as you are haveing. Also could be the ecm (aka)computer in your car is going bad. You can get a remanufactured one cheap. And it is simple and strait forward

Did you check the park fuse, or the orange wire going into the headlight switch for power ?

Your brake lights and hazard warning lights should not work without the fuse installed.

I would check the turn signal switch. The cruise and turn signal are on the same switch. The brake lights go through the switch before going to the brake lights. And the turn signals don't work with the ignition off.

i have a 90 chevy 2500 2wd 350ci.when i go to start my truck the key turns hard in the ignition,the check engine light and brake light come on the heater dont work,and the transmission will shift from 1-2 at real high rpm and shift hard,no 3-od.this comes and goes,but all happens at the same time.some times it last for 10 min,sometimes its days.what is going on?

the signal from the brake pedal goes to the turn signal switch then to the brake lights, check that circuit

i cant spell but try the starter cilanod

I had the same problem with my 1998 Cavalier and it was the wiring harness which fortunately is under recall if you call your Chevrolet dealership in your area.