just picked up a 90 GS and the reverse light doesnt work, im not sure where to start looking i already changed out the bulbs.

ALSO i got some spongey brakes i blead them already no air, when stopped i can pump to get pressure, but at idle it climbs alittle when i pump it. could it be a vacuum line from the booster??

 

Your reverse light has nothing to do with your brakes.

 

i know thats why it says ALSO, its two different problems

 

This is the exact stuff that gets nothing solved for anyone and also why people get angry for if i was told that in person i would have punched that person in the face for such a stupid answer.

Now onto the op's original problem.
Quick google search and i found what i would believe to be the problem it was actually the first thing that popped up for future reference.Heres the link:http://forums.g2ic.com/archive/index.php/t-136096.html?

 

I had this problem one time, the wires on the reverse sensors on the transmission had a bad connection, i rewired the plug and connected it back to the sensor and the lights were working again. Check your wires around the trans

 

I would of shot you! go figure