I'm trying to diagnose my 97 blazer right now as the other day my turn signals and brake lights just stopped working. So far I've ruled out the fuses and flasher relays. At this point I've narrowed it down to one of three things: multifunction switch, bad ground, corroded wire.

I've got the dash apart and the multifunction switch out but still connected. What pins could I jump to possibly rule out the switch? My haynes manuel only has a very basic diagram that isn't really much help.

 

First a question. Are the front flashers/turn signals working and only the rear lights are out? Or are the signal lights out on all 4 corners? If the fronts work and the rears are out, it's much more likely to be the ground(s) in the back.

I've got a Chilton's, with a "typical exterior lighting system wiring diagram" here. I can't say if it's any better than your Haynes, but here's what it has in the wiring diagram.

Pin 16 going to the switch is power from the turn signal flasher. It might be purple (no guaranty on the color). The rear turn signal wires are on pin 18 (maybe yellow wire) for the left and pin 19 (maybe a dark green wire) for the right. Power from the brake light switch is on pin 17 (maybe white wire) and goes through the multifunction switch to the same pins (18 and 19) and wires to the tail light assemblies.

Your wires may vary. Hope that helps.