Hello!
1. I've got an issue with a malfunctioning left brake light. When the running and head lights are on, the brake light doesn't work, but when lights are off it is fully functioning.

2. My right turn signal (rear, all of these issues) is non functioning. Bulbs are good.

3. Upon inspection and troubleshooting i found my third brake light had burned out as well. Its late and i can't replace the bulb now (obviously this is the next logical step), but i'm wondering if all these issues could be related and possible attributed to a ground fault somewhere. In which case, where's a good place to start in finding the potential ground fault? Thanks!

 

Abel, these sorts of problems can happen with really old bulbs, not because the filaments are broken, but because the lead terminal ends have deformed from years of heat and vibration. You may want to buy some replacement bulbs, swap them in, and see if they fix your problem. I had this problem both in two old Saabs and in our old Range Rover Classic. Bulbs are relatively cheap, so there's low financial risk here.

Simply replacing the bulbs may not solve this problem, however. You didn't say where you are in the world, but in parts of the country that salt roads or in areas with salt sea air, the grounds may need to be cleaned and sprayed with silicone spray. Grounding is really insidious. With poor grounding, electricity can choose to follow paths of least resistance, even flowing backward through both filaments, lighting both poorly. Check out some videos on finding all the electrical connections and grounding points, and clean them. This is not easy work, but it pays off in the end.

Good luck,
Scott

 

old lamps or a bad ground. Check the lamps first, they are cheap.

 

Two ideas:

1) On mine it was a ground in the right rear causing similar issue -- there is a ground on both sides. See image below, there's one on each side of the rear cargo door behind the trim.

The photo here is passenger side, it's the same on the drivers.

2) Also when the taillamp circuit boards get wet on the rear of each upper taillight, on the 99-02's, it causes this exact issue.

 

Had a similar problem. There’s 2 10A fuses for your low beams (one for left and one for right). When my right fuse blew, it took out my right brake lights. Note, my right low beams weren’t working either. It’s possible this was caused by some sort of short somewhere, but for now replacing the fuse fixed my problem.
Fuses are under the steering wheel. Cant remember the numbers, but just look at the images. Have you checked these?