Left brake light goes out when headlights are on

I'd check the rear sockets for proper ground , old worn sockets can do funny things , you'll need a multi tester , if you are going to do these types of repairs there are certain tools you will need , take a look at the wiring under neath

Thanks beatupchevy, i will check them out, although I do have new sockets and circuit boards. Would a bad ground cause this kind of problem?

It could , every thing needs a good ground , the circuit will find another ground if it doesn't have it's own , it can be weird shit , path of least resistance , even if it's just a little , it's an old vehicle you have to tear through it some times

Thanks once again.ground on left side underneath was questionable and old brittle wires along frame causing problems.

Beatupchevy you ate right about older rides.mine has developed a knock under accelerationI thought maybe bad gas, but high octane gas, octane booster and even Lucas didn't quite it. I'm thinking Timing Gear , timing chain is a good place to start if timing is off...it still starts good but has an erratic idle and doesn't run as well as usual. I should mention that ever since I bought the truck, that it smokes for a short period of time after it sets without running for several hours. I know that is worn valves or valve guides seeping oil into the cylinders. Any thoughts on these issues?

smoke at first that clears up sounds like piston rings , a knock under acceleration sounds like worn timing chain , if the frame isn't rotted out in the truck I'd keep it , while the technology is good for mileage and performance I think they over do it and make things difficult