RE: 90 accord brake light problem
Check for a bad ground at therear lampclusters.
Then check for an un-wanted connection between brake & taillight circuits at the rear lamp clusters. This can also be caused by bulbs being installed wrong.
The combination brake/tail lamp bulbs actually have 2 filaments, & they have 2 little contact nubs at thier base. They're only supposed to go in the socket one way, but they can be forced in backwards to cause this problem. Or... a single-filament bulb was installed where it should be a 2-filament bulb.
Or... one time I saw the 2 little contact nubs at the base of a bulb had been mashed so the contacts inside the bulb socket would touch both nubs together.
'05 Saab 9²x aero (RIP)
2 '07 Civics
'09 Saab 9³ss
'10 Saab 9³sc