I have a 2005 Express 3500 passenger van. My break lights, blinkers and reverse lights work fine. But my park lights do not. I replaced the bulbs and all associated fuses, Verified relays with multimeter, verified ground with multimeter and even change the ground verified it again and still no sauce. Ive got 12v to the socket where the bulb plugs in, still no light. In my last effort to try and see some light at the end of the tunnel I robbed park lights from the trailer light harnes after verifying it worked and still nothing. I have no clue what to do next.

 

If you've got 12v at the socket then the bulb must not be making contact or it's somehow the wrong bulb. Check for corrosion in the socket. It's possible that you could get 12v with the meter probe but not with the contact on the bulb.

Check that you have the right bulb. It should be a dual filament bulb but a single filament will plug in and possibly give you a brake light.

Check back in and let us know.

 

Here's the wire diagram.
https://charm.li/Chevrolet/2005/Expr...20Diagram%205/

 

Yea I knew about the double filament. I had someone hold the breaks and let off so I could determine which pin they were. Then did the same with the light switch to the left of the steering wheel. All 3 running lights in the rear are not working. left, right and upper middle. But all 3 break lights come on fine when you hit the breaks and the blinkers work fine too.

 

Not to be funny but are you sure the headlights are on? The auto headlights on my 11 don't come on until I take it out of park if it's light out.

If you're not getting 12 volt or ground at the socket pins then you'll have to trace it back to a point where you are getting it. That wiring should be pretty accessible once you remove the interior panels. I included a picture of my cargo van. I imagine the wires run the same way.

 

You may have 12 volts at the light socket but that isn't conclusive. You need to use a test light that has an incandescent bulb in it. NOT one with an led bulb in it. The volt meter or LED don't put any load on the circuit where an incandescent bulb will. If you have excessive resistance (corrosion) in the taillight circuit the test light either will be dim or not come on at all.

 

Just a quick one which may not be at all useful right now - rather than not post due to time and travel -> i thought I'd throw in that the BRAKE PEDAL SWITCH on my 2010 Savana caused many rear light issues - they're electrically related i believe.

EDIT; I'll leave the above though I've just realized it's the center-high rear brake light that's electrically connected - YET i did have "lights staying on and other brake and rear light issues", ALL related to the brake pedal switch ON the side of the brake pedal - i took it out (didn't replace though i did buy a new one) - i cleaned the old one and confirmed the wide-thin switch-button in it was free enough and toggling i think it was. put it back in an problems gone.

NOTE; very easy for to to order the slightly wrong brake pedal switch which i did initially as they look the same - important of course to get one for correct vehicle i found *-)