got an 89 with the ls1 that will start up and run untill i turn on my headlights and sometimes when the brake lights light up it stalls. it stated doing this a week or two after i put in a new alt and i was on my way to work. i was driving and came to a red light, applied the brakes and it stalled and wouldnt start back up till i shut the headlight off. runs GREAT when the lights are off. alt has been checked 3 times to make sure it is not the prob. between me and others we have checked the fuses, wire connections, relays, ect ect. i have no other clue to what it might be. please help.

you sure thats an ls1 engine?I remember it being an l98 corvette engine?Unless you changed it? Take a look at the bulkhead connector.Maybe someone like BigBabyLou will chime in here.There is TONS of info and great folks here that will help.

Oh yeah,welcome to TGO awinders!

If it is a "LS1" conversion........

Check your grounds!

The headlights are hot all the time thru fusible links
the tail lights are fused power.

Maybe your problem is in the parking light circuit?
They go on with your headlights and it seems to happen when you hit your brakes.

remove the stop / haz fuse, tail fuse and turn - b/u fuse - see if it still happens.
If it doesn't then insert one fuse at a time until the problem reoccurs.
At least then you will know what circuit you have to concentrate on.

You are either grounding out somewhere or a ground is not making good connection and the lights are finding ground through another circuit.
Since the parking and stop lights are a battery circuit, you could be drawing too much amps from a direct short to the battery.
Maybe!

I had a bad bulb in the tail light of a car that when I hit the brakes the parking lights and the dash lights would go on.
It also would make the engine do weird stuff.
It was a bad bulb.
It lit but the glass part of the bulb spun in the brass socket.
Electricity does some weird stuff sometimes!

Its not an ls swap Not that that matters though but yeah man,possibly a bad ground??The batt. ground cable is connected to the aluminum head.

If anyone cares....awinders and I fixed the problem yesterday.Turns out the ground for the entire car on the pass. head came loose.Tightened the bolt back up and everyone is happy!!YAY!! Hey awinders,when ya gonna post up some pics of that beast?You can just steal my pics if ya want.LOL!!