I just got a 89 bronco the bck window is jammed because it rained in gears rusted them what can i do to get it open and tailgait down?

best thing to do is take it to your local lock smith or a place that replaces car glass,eather can get it open.

try some pb blasterto loosen them up

try crawling into the back behind the rear seat. take a #2 phillips with u. remove the 10 or so screws that hold the motor access panel. the motor and regulator assembly should be exposed after u remove the plastic or paper sheeting used for a vapor barrier. you should have access to the bolts that hold the motor/regulator in place. BE VERY CAREFUL! the glass is heavy and has a large scissor type spring that assists the motor in lifting the glass. once the glass is loose in the door, u should be able to lower it enough to allow the rear gate to be lowered for easier access to the components. take your time, pay attention to how things come apart, and most of all, be gentle. these parts are old and fragile. i would do this job in a garage or during the summer/dry months. just in case u cant get it put back together in one day. start early and give yourself plenty of time. you'll need it. good luck!

make sure everything is very clean before you start reassembling anything. be sure to replace the rear gate seals or youre just wasting your time. these seals are availible new aftermarket from LMC and are good quality. once you get the regulator out and clean, lubricate it liberally with either silicone grease or white lithium grease. once you get everything back in, test the motor (with the gate up or it won't work) before your final assembly. before you reinstall the access panel replace the vapor barrier with thick plastic (black garbage bags work just fine) and tape or silicone. at this point everything including the gate should have been wiped clean. otherwise your tape/silicone won't stick.