1997 s10 brake light low voltage

I'm working on a 97 s10 for a friend and his passenger brake light is dim. There's 12v to the drivers bulb with the brake depressed, but only 9v to the passenger side. The bulb lights, but just barely. When the blinker is on the bulb lights up fine. Any leads would be appreciated.

One of two things: It's either a bad right rear socket or a poor ground for the right rear socket.

After chasing grounds from the back to the front, it wound up being the equipment ground right off the battery. Wouldn't you know, suddenly the blinkers that haven't worked forever started working. I was going to replace the multi-function switch. Glad I didn't.

Ok, just replaced the fuel pump, and now the truck was missing for a day and then the ECM fuse blew. Any suggestions? Every other site suggests a short somewhere, but chasing shorts in that engine bay will be a PITA.

There is a ground splice pack just ahead of the rear bumper. Several ground wires all connect together and then one wire is grounded to the left rear corner of the frame, (gotta feel for it on top of the frame). Tail lights, turn signals, back up lights, brake lights, fuel level sender, and even the fuel pump, all ground at the same place. Might be the whole problem... take the bolt out and clean the connection with a wire brush, then check all connections in the splice pack.

Thanks, we got the lights working, and the fuel pump sorted. Starting and running consistently now. There was a BIG wad of wires up against the exhaust manifold, 4 wires were fused together sending straight battery amperage to the fuel pump resulting in that burning out and blowing the ECM batt fuse. Fixed the wiring mess, and now the last issue is that it's missing on cylinder 3. Too tired to investigate this evening. I know from earlier today that we have at least SOME spark to that plug, and the injector is pulsing. Gonna have to see what's going on with it tomorrow.

Sounds like a mess to me! What engine is in the vehicle? Is the check engine light on? If so, what codes are stored?

Fortunately an easy fix once I found some time to actually do it. The code was p0303 iirc. Misfire #3 cylinder. Turned out to be a plug wire that normally showed 10k ohms, but when it was flexed or vibrating went to 72k ohms. It was just losing spark while it ran. New plug wires and back on the road with the SES off for the first time in years.

Good job, thanks for posting back.