Baffling electric issues

[BigArt]

Here's the deal and before anyone says check the grounds, I've done that. All checked and cleaned. The problem I'm having seems to come from only one circuit. That is the Orange circuit coming off the ignition switch. It feeds/controls CRUISE, 4WD, BRAKE, and HEATER A/C. All other circuits work fine, and the truck runs fine. Heater control is flaky. During the summer, I had to run a separate fused line to the heater control in order to have an adjustment for the blower motor. But the vent doors are still sluggish, and I'm not sure that the temperature control works. 4WD does not work at all. Have actually changed the 4WD actuator. CRUISE seems to work most of the time. Sometimes not. The ABS hasn't worked for many years. The ABS light is always on. Some testing results and always testing the Orange wire from the ignition switch, or at the fuse box (same results):
With all fuses in: Reading 8 volts.
With all fuses removed: Reading 14 volts.
With only Cruise fuse in : 14 volts.
With only 4WD fuse in: 14 volts, UNTIL I engage 4WD, then zero volts.
With only Heater fuse in: 8 volts.
With only Brake fuse in: 11 volts.

I initially thought it might be a faulty ignition switch, but I'm not sure now. It may be, but why the good reading, until I plug in the heater or brake fuse, and why zero volts when 4WD engaged? Any other thoughts, suggestions? I have detailed wiring diagrams, will post the offending circuit for your reference. Thanks.

 

[Matt Bachand]

Defanately not a vacuum system?

I have different year, but all those things sound easily controlled vacuum designs on alot of vehicles.

A quick thought.

 

[jbsaxman]

No, the only thing our rigs use vacuum for is EGR and WG.

 

[Matt Bachand]

No, the only thing our rigs use vacuum for is EGR and WG.

What i thought, wasn't sure of older years, my buddies gasser gmc all that stuff is vacuum, either way, explains why they are all releated.

 

[hereismylife]

it still could be a bad ground connection or wire. ( just a thought) I did see you did check them. Also it could be in the fuse box. it could be alot of things off the top of my head. Maybe if you fix one of the problems you will find your answer to the rest.

Sounds like you have possibly a bad ground or wire....

I did have my ignition switch go bad and had alot of things go crazy.

Did you check at the steering column before and after the switch for 12v?

 

[chrisk1500]

4 volt drop after installing heater fuse?

That's where I would start....

 

[docdray]

sounds almost like a high resistance open, where the wire has a bad splice or bad connection-possably bad ign switch. --with no load, voltage is ok. as soon as load applied the voltage will drop. verify voltage before ign sw with fuses in, then on orange wire. if voltage drop after sw-its the switch. if bad voltage before ign switch, trace back. as I am sure you know, blown fuses can still read proper voltage, but carry no load.

 

[just a number]

:iagree: That's what I was thinking.

 

[corolla]

There were problems with the heater relay located above the heater fan, just below the ECM (access via glove box).

 

[BigArt]

Yah-Hoo - solved!!!

I've been battling electric gremlins for the past year. Well, through members help from this forum with diagnosing and how-to, I installed a new ignition switch (it wasn't cheap) yesterday. It solved all my issues. 4WD works! Heater controls work! Cruise works! WHAT AT TREAT! Now I have some faith in the beast again, and will get on with some other mods. Exhaust, turbo-master, gauges, and perhaps a "chip". Thanks to all who had some input into it! - Art

 

[Sunshine]

Yah-Hoo - solved!!!​

That`s good to hear Art, the sigh of relief, don't let them gremlins near your Truck again..

 

[Turbine Doc]

Behind the glove box is a red wire, black connector, that carries the power for the blower in high speed, often the connector melts from hi current draw and a intermittent connection is made, acting like bad blower control, had pics of it on the other site

 

[hereismylife]

I am glad you got it fixed. I did talk to chevy about this problem. they say it is a common item to go bad. In fact the one mechanic tore one apart to see why they go bad. He said just all the little connectors go bad inside and not worth fixing. To me it was like driving a whole new truck when mine went out.