Oldsmobile/Buick Repair: oldsmobile bravada, alternate power source, oldsmobile bravada

Question
98 olds bravada smart trac(automatic 4 wheel drive). Has blown fuse in underhood fuse and relay center, and 4x4 doesn't work. Replace fuse and as soon as one wheel slips it goes into 4x4 and immediately blows fuse. Unhook shift motor on t-case, replace fuse, will not blow fuse. Energize shift motor with alternate power source, seems to work fine ( motor runs both ways). Why does it blow fuses when the shift motor is hooked up? What sends power to the shift motor, and how does it know when the shift motor is at the end of its cycle? Detent switch in t-case? Contacts in motor? Does this t-case have clutches in it?

Answer
HI STEVE,SMART TRAC NOT TOO SURE ABOUT THAT LOL.THE SHIFT MOTOR CONTACTS TELL THE MTR WHERE TO STOP..THE MOTOR IS POWERED FROM A RELAY.IT WORKS FINE ON ALTERNATE POWER SUPPLY.AND WHAT IS AN ALTERNATE POWER SUPPLY,JUST A DIFFERENT HARNESS.TRACE YOUR HARNESS YOU WILL FIND A SHORTED WIRE SOMEWHERE IN THE HARNESS FROM T CASE TO RELAY .GOOD LUCK PLEASE RATE MY HELP TY BILLYMAC