Check connections and the switch on the 4X4, it obviously is powered by the heater fuse and nothing will work if the fuses are blowing cutting power to the whole system
SOURCE: 4 WHEEL DRIVE DONT WORK
first off your heater dial swithc is buggered. and as for the four wheel drive is it all electric diff locks or do you have to get out and lock hubs in etc?
SOURCE: 4 wheel drive won't work
There is a vacum powered actuator on the front differential housing on the passenger side. It gets it's vacum from two valves mounted on the firewall just behind the battery(to left). The white line feeds manifold vacum to the valves. Check for vacum at white line with engine running. If no vacum there is a break in line from manifold. If vacum check the pink and blue lines by applying vacum to each one. The vacum should hold. If not check lines from valves to vacum actuator. Most likely it will be the actuator. If both lines hold vacum check valves. Remove electrical connectors from both valves. Connect a wire from one of the terminals of the valve to ground. Touch a wire from the battery + to the other terminal of the valve. Listen for a clicking sound. If no sound valve is bad. Replace valves(s). If this doesn't lead you to the trouble it's probably a mechanical problem inside the differential. However most likely there would other noises.
SOURCE: Lights flashing on 4 wheel drive panel
the front actuator is not working..If you open the hood and under the battery is the plunger that pulls the cable for the 4x4..If theres a vacuum leak it will not in gage.It could also be the sensor in the transfer case..What you could do is you may have to pull the tray out that holds the battery in and see if the actuator/plunger has a hole in it..It looks like an old chevys cruise control but it is directly under the battery...You can pull the plunger in and try and move the car to see if it locks in to rule out any bad parts in the front axle..If that works the problems a little easier to figure out..Either the plunger has a hole in it and cant hold vacuum or theres a hole in the vacuum lines to it..The vacuum lines also run all the way back to the transfer case also so they could have a hole in them also.If those are all good then the sensor in the transfercase on the top of it and its either a three wire or four wire is bad..Hope this helps you have a great day
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1988 GMC 2500 4x4 Truck
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