94 Mazda taillight bulbs?

Ok I replaced the 2 rear taillight bulbs. With new bulbs and they still arent working. The fuse is still good and everything. I did notice that my left rear taillight has a small crack at the top and water is filling up my left taillight everytime it rains. Can this be effecting my wiring at all? Also when I hit my brake lights my stock radio light dims in and out. Then when I put on my turn signal to turn the radio and arrow on my dash dim even more. Does anyone know what could be going on here? Thank you all.

Sounds like you have a poor connection. You probably have corrosion built up that needs cleaned out. The main tail light harness has a disconnect under the bed above the spare tire carrier that you may need to test for volts but before that try this. Each tail light bulb socket disconnects from the harness. Disconnect them all and test each one, one at a time plugged in. If it's corrosion it shouldn't have gotten that far into the harness.

Ok thanks. I will try that. Also what tool can I use to test that?

The first test you don't need a tool, the other test I was talking about you would need a voltage reader.