'97 GMC K1500 4WD Not Working

I have another question about my new-to-me '97 GMC K1500. The four wheel drive does not engage on the front axel. The transfer case seems to work. I can shift it to 4 low and it spins the rears slowly, like it's supposed to. The bulb on the floor shift indicator is good.

I checked the front thermal actuator, by giving it 12 volts and it works fine. I also checked a spare a friend had, and it also worked fine. I don't get any voltage to the thermal actuator when I shift to 4wd.

So, it would seem that I have an electrical problem, and not a mechanical one. I have tried to find a schematic for the transfer case, but haven't had any luck yet. There are 2 connectors on the case. I think one is for the speed sensor, and the one on the top for the 4wd engagement. Does anyone know if this is correct?

How does the front thermal actuator get its juice?

Thanks, Tim in Mass

Unplug the switch elec. connector at the top of t-case(not rear as it's a speed sensor) and see if voltage there.If you do,the switch is bad.If not,pro'ly a fuse or broken wire.

And, that fuse runs something else too. Darned if I can remember what it is right at the moment, but there is another system on that fuse.

Allan

Check to see if a dime or penny is in the aux.power socket.Looks like a ciggy lighter...How many pennies have ya found in ciggy lighter sockets at the dealer Allan? Short to ground every time.

Tim

If you check the archives, I posted the part numbers a couple of months ago. I don't have then "at hand" at the moment.

You still need the old electical system to be working, though, as the new stuff is an "add-on" to it.

The replacemeny actuator is a linear gearmotor, so engagement is instant, instead of waiting for the thermal unit.

Any GM dealer can easily look up the parts. They are more expensive than they used to be, I think the actuator plus the conversion harness will set you back the better part of $200.00.

Power goes from that fuse to the transfer case switch that I THINK you have correctly identified.

When you shift the xfer case into 4X4, that switch sends power up front to the thermal actuator.

When the actuator pushes the axle disconnect into "lock" position, there's a switch on the front axle near that actuator that closes, and lights up the 4X4 indicator as the axle disconnect engages.

Probably that switch on top of the transfer case.

Allan

Regards, Tim Hynes

I found the fuse and it was blown. I replace it and it blew again when I put it into gear, but not right away, it took a few seconds. So this means I don't have a direct short.

I put my other thermal actuator in from my '88 truck, this one works fine, and that also blew the fuse. I checked the resistance of the actuator and it was 1.1 ohms. That means it draws about 11 amps. The fuse was 25 amps.

I have an electrical problem. I now suspect a corroded wire, or the switch on the top of the transfer case.

I ran out of light and ambition to track those down tonight.

To be continued...

Unplug the electrical connector at the transfer switch and see if it still blows the fuse. If it does, the problem lies upstream of the transfer case.

Also, there is something else on that fuse; just can't remember what the heck it is right at the moment.

Allan

I unplugged the second electrical connnector on the front axel and the fuse does not blow and the axle engages.

It seems that this second connector, is to blame.

I think that this is for the indicator light on the floor shifter? Does anyone know for sure if this is the correct, or if this switch goes to the computer for feedback to the ABS, or some such...?

Regards, Tim in Mass

Should be getting easier to find at this point.GREAT WORK !! Just a process of elimination.