Rear Brake Light Issue

[JeepmanMcGruber]

I scored a '98 that had a little front end damage to it. got everything squared away, but my brake lights are acting up.
When the lights are off and push on the brake, the tail lights light up fine.
however when the lights are on and push on the brake, the tail lights don't really get any brighter.
The driver's side is stock with harness, and it seems to get a shade brighter along with the aftermarket LED 3rd light. But the passenger side tail light was replaced and wired together without the harness. I don't notice that getting brighter at all.
My first thought was the brake relay, but if it was bad, then the brake lights wouldn't work either way.
Anyone have issues like this before?

 

[dan lee]

I would check your ground at the tail light, I believe it is a floating ground. Tighten up the bolts that mount the light to the tub.
I found this out when I went to install the rear tail lights guards.

Show us some pic's when you get time

 

[mrblaine]

I scored a '98 that had a little front end damage to it. got everything squared away, but my brake lights are acting up.
When the lights are off and push on the brake, the tail lights light up fine.
however when the lights are on and push on the brake, the tail lights don't really get any brighter.
The driver's side is stock with harness, and it seems to get a shade brighter along with the aftermarket LED 3rd light. But the passenger side tail light was replaced and wired together without the harness. I don't notice that getting brighter at all.
My first thought was the brake relay, but if it was bad, then the brake lights wouldn't work either way.
Anyone have issues like this before?

I have seen folks shove the tail light lamps in the wrong way. I have also seen them use the wrong lamp. IIRC, the correct lamp has offset pins on the base with one higher than the other to orient the lamp so that the brake filament and running light filaments get power at the appropriate times. There is another lamp that will fit into the same socket that has pins opposite each other and only has a single filament. Check them to see if you have the right lamps.

I suspect if the ground at the light housing were bad, the lamp wouldn't work at all not just on one filament.