The Car:
99 S70 Non Turbo

This car was donated to me because the PO didn't need it and it was having multiple issues.

1st issue i resolved was, it wasn't running, through research I found the fuel pump relay to be bad. viola!! car runs great now.

The issue I'm having now is:

The tail lights don't work when the headlight switch is on. Brake/turn/bright/dim work fine.

I've narrowed the problem down to fuses 23 & 24. with fuses in both or just one or the other....fuse 26 blows.(light switch)
I've unplugged all lamps and harnesses and the fuse still blows

I'm about to the point of wiring the tail lights hot when the key is on.

Please help!

 

You may have to spend some time with a multimeter and visually running each wire as much as possible. The light switches on these cars are troublesome and, although I haven't heard of your particular problem, I would start there.

I know it's not much help but it's the best I could do. Oh yeah, my experience with Volvo lighting harnesses (I have 2 Volvos) is that they seem unnecessarily complicated with multiple fuses and bulbs that blow for no apparent reason, but eventually there is a solution. (I spent a week trying to get my S80's headlights working only to solve it by checking EVERY fuse. The culprit wasn't even related to the headlights!) But hardwiring the taillights just seems like begging for trouble to me.

 

Unplug the head light switch then install a fuse and see what happens.