Here's a new one. I have an 88 GT with factory performance sound and T-tops. The speaker was blown for many years so I had it disconnected but after replacing the speaker and getting it up and running, I notice the subwoofer goes in and out between the correct slider setting and full bass for periods of time as I'm driving. I tried switching screws and shimming with washers and other things at the dome ground and I was racking my brain trying to figure out what's wrong with the grounding.

I know the T-top section is riveted to the original Fiero roof. This is just a theory but is the T-top riveted roof section not well grounded which could lead to the dome slider subwoofer ground coming in and out of contact as I'm driving as the body flexes? If I'm not mistaken an ungrounded dome light results in full sub, and when it is properly grounded it uses the slider setting. The only caveat to this theory is the lights all seem to work normally which are also grounded to the roof, although I haven't really used the dome lights while driving.

Anyone else experience this with the T-roof? I'm thinking I may try to run a ground wire from the dome down the pillar and ground it to the chassis near the fuse box and see if that fixes the problem, but wanted to see what people's thoughts are on this one before I take the time to pull the headliner and trim.

quote Originally posted by reinhart: Here's a new one. I have an 88 GT with factory performance sound and T-tops. The speaker was blown for many years so I had it disconnected but after replacing the speaker and getting it up and running, I notice the subwoofer goes in and out between the correct slider setting and full bass for periods of time as I'm driving. I tried switching screws and shimming with washers and other things at the dome ground and I was racking my brain trying to figure out what's wrong with the grounding. I know the T-top section is riveted to the original Fiero roof. This is just a theory but is the T-top riveted roof section not well grounded which could lead to the dome slider subwoofer ground coming in and out of contact as I'm driving as the body flexes? If I'm not mistaken an ungrounded dome light results in full sub, and when it is properly grounded it uses the slider setting. The only caveat to this theory is the lights all seem to work normally which are also grounded to the roof, although I haven't really used the dome lights while driving. Anyone else experience this with the T-roof? I'm thinking I may try to run a ground wire from the dome down the pillar and ground it to the chassis near the fuse box and see if that fixes the problem, but wanted to see what people's thoughts are on this one before I take the time to pull the headliner and trim.

This was my first thought too... assuming the slider has good contact and is not dirty / worn... then I think it's likely a ground issue, and as stuff moves around... you're losing your ground.

Are you sure that the connections on the speaker are good? Did you solder them to the leads?

The dome light/slider assembly is screwed into the metal panel below the outer roof skin and above the headliner. If the lights are working, it is grounded.

I would clean the slider with some contact cleaner.

quote Originally posted by 82-T/A [At Work]: This was my first thought too... assuming the slider has good contact and is not dirty / worn... then I think it's likely a ground issue, and as stuff moves around... you're losing your ground. Are you sure that the connections on the speaker are good? Did you solder them to the leads?

Definitely not a speaker issue as bad contacts on the speaker would go between no bass and slider value bass, not between slider value and full bass.

I guess no one else with T-tops has encountered this issue. Figured if my theory were correct others would have had a problem.

I haven't been driving with my dome lights on so can't confirm if the lights are losing ground as well.

I'll either swap out a different dome light assembly or drop a wire down from the dome light ground to the center console at a known frame ground point, and see if that makes a difference. Put that on my list of projects.

quote Originally posted by reinhart: Definitely not a speaker issue as bad contacts on the speaker would go between no bass and slider value bass, not between slider value and full bass. I guess no one else with T-tops has encountered this issue. Figured if my theory were correct others would have had a problem. I haven't been driving with my dome lights on so can't confirm if the lights are losing ground as well. I'll either swap out a different dome light assembly or drop a wire down from the dome light ground to the center console at a known frame ground point, and see if that makes a difference. Put that on my list of projects.

my gtp does something similar. see if the headlights being on or not affects it, if it makes it louder then you have a bad ground for your instrument cluster and supporting area, if not then start checking the slider connection with a multimeter to see if it's resistance range is correct (not too sure if you can or not since I have yet to see a performance sound system car)