I helping out this guy I work with fix a few things on his 2000 S10 4x4. The one thing I need a hand on is that the taillights/front markers are on with the daytime running headlights now - all the time. When you turn the headlight switch on, all the lights work properly, but when the switch is off it has markers and headlights on still. Signals and brake lights work fine. Also his fuel pump is very loud, is it on its way out? This must be the loudest fuel pump Ive heard.

 

I think your brake problem is a bad brake switch or something in the wiring is bad.
As for the fuel pump I'm not sure.

 

middle of the day or night, when the trucks running, its park lights are on. Even when the switch is off. When you step on the brake or signal they work fine. Its just strange that this started to happen.

 

Sounds like an unrelated problem. You don't happen to have something covering the ambient light sensor on the dash do you?

 

The ambient sensor is the little nub on the passengers front dash speeker grill at the windshield, like Swartlkk said either it's covered or someone's unplugged it. If it is unplugged it will cause the automatic lights to come on as soon as the ignition is in a on or run position. If it's not covered your going to have to unscrew the cover to check if it's unplugged.
While your in there and if you don't want automatic lights you leave it unplugged from the sensor and install a 1,000 ohm resistor into it (Radio Shack sells them in a pack of four for 98 cents,just stick one side of the resister into the plug and loop it back to the other side of the plug). This makes the computer think it's daytime all the time and keeps the automatic lights in the off position. You still have the light switch and if you want to get rid of the daytime running lights pull the black diode in the fuse panel under the hood marked (DRL) looks like a regular relay only black not grey, bend over the tab marked 86 and reinstal if you don't reinstall it you'll loose the drivers side high beams). With these two mods you have complete control over the lights via the light switch. My bet is someone was doing a speaker upgrade and never plugged the sensor back in.

 

Wicked help dudes! Ill check it out for him tonight at work. Rock on.

 

Hmm that's a good point I never thought of that one.

 

Fuel pump might be on the way out but try changing the fuel filter. A plugged one will make the pump noisier.

 

There is a multi function switch in the steering column that Chevy has recalled. It runs the brakes lights, bright lights, cruise, blinkers ect. Could be the prob. I replaced mine twice and then the Chevy house did it for free again last week.

 

Could I ask if you ever got the light problem sorted out? I have the same problem on my jimmy