88 Gmc K2500 Wiring Diagram

Ok,
I've got no 4wd after having the truck exhaust worked on and new tires.

searching the web and crawling under the truck takes me to no current at the actuator, trickles abit at .5 to 5 volts... Kinda tells me a bad connection somewhere.

The view is that it has been upgraded to the motor, wire spliced at transfer case switch.

Transfer switch splice was a crimp connector very close to the switch with no silicone and no tape etc... I'm guessing this is the problem, probably corosion?

Anyway, they left very little wire out of the switch.

Beings Its on top of the transfer case, and I cant see much. Does anyone know if that wire is part of the switch or has a connector? I dont want to yank on it and break the switch untill I ask an opinion.

I'm on my back working on it, cant see much at all but the crimp connector sticking up..

Any advise?

Can I by pass the switch all together with a toggle?

Should I just by a new transfer switch? Hard to change?

Being an 88, exterior wires and connectors seem to be desintigrating.

I'd like reliability, so by passing all the connecters would probably be a blessing, but I dont want to burn the actuator up or break anything by bypassing things.

Anyone familiar with these actuators and switches?

Anyone happen to have a wirring diagram for the three wire actuator and where each go?

The wires get lost in a harness or two and several connectors.

There should be a switch on the transfer case that goes to a solenoid which powers the actuator on the front axle. This is a lever shift 4x4, right?

I've got the diagram from my 1992 GM Manual, Let me see if I can get it online for you.

There is a switch on transfer, but I didnt know about the relay, where is that located?

Yes, it's a lever shift on the floor, with a wheel diagram that lights the front wheels when in 4wd.

On an 88,you should have a two wire actuator.

Power comes from the Heater\AC fuse to the transfer case switch on the brown wire.Check and make sure you have a constant 12V there at the transfer case switch.When in 4WD,you should see 12V out on the blue wire at the transfer case switch.If you have 12V,the switch is good.If not,replace,or make sure the case is shifting into 4WD fully.If you have 12V,then most likely you have a broken wire between the switch and actuator (blue) if your measuring less than 12V at the actuator.Unless the broken wire is very obvious,just rerun a new wire.You'll spend to much time tracing the old one.

Thanks Chris,
Thats what I was after.

It was updated to the three wire system at some time, it has the motor actuator.

What I was after is what powers what wire.

I think the brown wire was the one spliced for the upgrade and Im guessing the fault, I'll check the voltage again upstream.

Thanks.

The extra wire is routed back,and tapped into the brown wire feeding the switch (12V) the transfer case.

It can actually come from anywhere that has fused key power.

After finding it difficult to make a secure waterproof connection under a wet dripping truck,I started routing them into the cab,and connect it to a fuse tap under the Heater\AC fuse (or the 4WD fuse on the newer ones).Easy to do,and keep it clean and dry.I bet whoever did it on your truck used a crappy scotchlock connector to tap the brown wire near the TC,and it's now corroded off.It may pay to check and see where it was tapped,as the scotchlock will also damage the original brown wire feeding the transfer case switch,which may rot off in the future,leaving you with no 4WD again.

I could fax you the original wiring diagrams,as well as the update TSB and included diagrams if you need them.

A way too big crimp connector .5" from the trans switch.
No tape, no silicone.

I'm afraid to touch it.

If you could fax, that would be great.

I'll PM the number, let me know what I owe ya.

If I run into the cab, can I just use a toggle switch?

I'm thinking ahead incase the transfer switch has no wire left on it to connect to.

Well your going to have to get in there,and repair it properly.

I would suggest removing the connector,and the harness,so you can get it out and work on it.

Cut out the stupid splice,and as much corroded wire as possible,and solder and heat shrink (you may have to add some wire).If the wire is too short,you may have to find another terminal,or another connector to start fresh.Doesn't matter which wire goes to which terminal.The only important thing is that the additional brown wire to be spliced in,has to be connected to the brown wire at the switch.

If the connector is screwed,and you can't find another one,you can put a regular toggle switch in the cab to engage it,instead of the transfer case switch.

I'll fax you over all the wiring diagrams.

Thanks Chris,

I'm fuzzy on how it works, If I power the motor in with a toggle, what shuts the motor off? And then how does it return to disingaged?

A linear motor, I imagine it has to "linear" itself back electricaly...

Maybe the diagram will tell me how this thing works.

What wire is doing what and when.

The original actuator is a wax pellet,which is heated by an element when powered.The wax heats up,expands,and drive the actuator out.When the heater turns off,the wax retracts and it disengages.

The newer ones are an actual motor,that's why it needs a third wire.

You should be able to find another typical GM weatherpack connector to replace yours if there isn't enough wire left to repair.

If you want a toggle switch instead,you need to tap fuse or good ignition power source and connect it to one side of the switch.Run the two wires from the actuator (blue and brown) into the cab.The brown wire will connect to the side with the power wire,the blue wire to the other side of the switch.If you go this route,you must engage the transfer case first,wait a few seconds,then flip the switch.You might have to move forward to get the axle engaged.

The 4WD indicator in the console will still work as normal.

Check your fax,hope you have lots of paper.

Get your butt to the next GTG,and you own me a :drinkup

Got it,
Ill post how it goes... There are a ton of threads on the internet with incomplete/unresolved ends on the subject.

See you at the next GTG!

:wink

Hope you get it fixed easily.

I'm going to move this to the Chevy\GMC truck forum for future reference.