I have a 94 chevy 4wd. Sporadically the 4wd stops working. When it does the 4wd light indicator stops working, the brake light comes on, the heater fan stops working and the speedometer stops working and the transmission seems to lose power. Where should I start?
I suggest you purchase a service manual for the vehicle that shows the wiring layout for the vehicle. Factory manuals are the best ones to get. It is a great investment if you plan to keep the vehicle. You may also be able to find information at your local library possibly.
Check the wiring diagrams power distribution panel and find where the circuits you mention tie together. They most likely are tied to a common fuse point. Then start looking for a bad connection down the line. You can also check the fuses in the dash and the panel under the hood to see if there are any fuses not getting power when the trouble happens.