Intermittent left F/R speakers?
 

I have a 1986 FC/NA with stock radio and speakers. No eq.
The left front and left rear speakers mostly don't work but sometimes when I go over a bump, they both simultaneously come on fine, and then work for a while until some time later (usually 5-10 min) when I go over another bump, and then will stay off for weeks/months until I hit just the right next bump again. When they are on, they sound fine.
Am new to the forum; lots of good info here though.
Any help on where the problem might be and how to fix it?

I need to introduce you to "CRC QD contact cleaner" from the electric section at Home Depot.
Good for stereo controls, logicon sliders & buttons, door lock position sensors, & TPS.
The only hard part is getting access to the volume & balance controls inside the radio.

That of course makes sense. I'll get to know Home Depot and will start from there; thanks lots.
Now I need to fix my clock, but I know already, that's a cold solder joint, and the horn too...

^ welcome to the world of elecrtical problems, (my car has the flashing seatbelt light going on 24/7, horn doesn't work, and interior light doesnt't work, also oil gauge broke and needed to buy after market gauge)

i know i'm bringing this back from the dead. but i have the same exact problem. did the contact cleaner fix the problem?