random wires and acc mode

[Tazix]

There is a connector with black and white wires running to it that isn't plugged into anything and I'm not sure what it goes to.

Also when I turn the key to acc mode nothing happens, any ideas what could be wrong?

 

[CRM]

Although I haven't noticed the wires you mention I also get nothing in the ACC position. Interested in what the answers to this will be.

 

[chengny]

There is a connector with black and white wires running to it that isn't plugged into anything and I'm not sure what it goes to.

If your truck were a V series (equipped with 4WD) rather than an R, those leads would be used to connect a switch on the transfer case with the 4WD indicating lamp in the instrument cluster. They are normally run from the fuse block/instrument panel to the firewall. At the firewall they disappear under the carpet, then they head down the slope and over to the transmission tunnel. They are routed through the T/C shifter cover and the hole in the tunnel. Once under the truck, it a straight shot to the switch. Depending on optional equipment, they can also be used for other purposes. With overdrive type transmissions, they form part of the TCC lock-out circuitry. On trucks that use an NP208 transfer case, the black lead supplies power to the shifter backlighting lamp. The wiring diagram below shows them being used in a truck with non OD transmission and a NP205 T/C. In this case, they are only used to illuminate the 4WD warning lamp in the IP.

You must be registered for see images attach

 

[CRM]

I've been doing a little studying on this because my ACC doesn't work and I have to turn the ignition almost all the way to start the truck. The most common reason found is that the ignition switch position needs to be adjusted. It has 2 screws holding it that need to be loosened and the switch is then moved towards the steering wheel. I'm going to try it soon to see what happens. They say if the adjustment doesn't work then it's most likely the switch. I guess we'll see.

 

[chengny]

Regarding the ignition switch not supplying power to anything when in the ACC position.

I meant to try and provide some insight into your concerns on that issue, but got sidetracked by something that didn't involve typing on a keyboard.

I suppose the main question is; What fuses/components receive power - and can operate - when the ignition is switched to ACC?

Also when I turn the key to acc mode nothing happens, any ideas what could be wrong?

I also get nothing in the ACC position.

You shouldn't expect too many things to operate when the ignition is in ACC. Below is a list of what is powered by the ACC. (BTW - the list is essentially identical for both the 1977 and the 1987 trucks):

Two are just two fused circuits in the main fuse block connected to the ACC bus; the radio and the windshield wipers/washer pump.

1. The 25A windshield fuse. This fuse is dedicated to the wipers and washer pump only - there are no branch circuits.

2. The radio fuse. In addition to supplying the radio with power, this fuse also feeds 3 branch circuits. All 3 circuits are for low load options/accessories and the the associated wiring is only included if the components were factory installed. The three branch circuits supplied are:

1. 4WD indicator lamp,
2. Automatic transmission kick down solenoid
3. Throttle stop solenoid

So, in CRM's case, even if you adjust your ignition switch perfectly - don't get your hopes up. About all you will be able to do is sit in the rain and listen to the radio.

The wiring diagram and a view of a real life fuse block (1977):

You must be registered for see images attach

You must be registered for see images attach

The same wiring diagrams for the 1987 - just all spread out:

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

 

[CRM]

I actually would like to be able to play the stereo in ACC mode while working on the truck. I want to re position the switch to start the truck without having to turn it all the way to the stop point.

 

[chengny]

You should do it then. Adjusting the switch position is easy and shouldn't take more than an hour or two.

The GM procedure for adjusting the switch is at the bottom.

I start in the engine compartment by releasing the transmission gear select connecting rod from the crank arm on the intermediate shaft.

Back in the cab, the lower column trim cover and dash filler plate come off:

You must be registered for see images attach

With those removed, you'll be looking at this - except your bezel and IP will still be there:

You must be registered for see images attach

Don't forget to release the clip on the end of the gear indicator wire:

You must be registered for see images attach

From where it clips to the bowl shroud:

You must be registered for see images attach

Then just release the two nuts that secure the column bracket to the instrument panel support:

You must be registered for see images attach

Lower the column until the steering wheel rests on the seat and adjust the switch as necessary.

Removal procedure per GM:

1. Disconnect battery ground cable.

2. Disconnect and lower steering column. Only lower steering column a sufficient distance to perform ignition switch service.

3. Rotate ignition lock to the OFF "locked" position.

4. If lock cylinder has been removed, pull the switch actuator rod up to stop, then down
to the first detent position as shown, Fig. 7.

You must be registered for see images attach

5. Remove column mounted dimmer switch, if equipped, then remove switch retaining
screws and switch.

Reverse procedure to install, noting the following:

1. Place gear shift lever in neutral.

2. Place lock cylinder and ignition switch in positions noted in step 3 & 4 above.

3. Fit actuator rod into hole in switch slider and secure switch with retaining screws,
ensuring switch does not move out of detent.

4. Install and adjust dimmer switch, if equipped

5. Torque retaining screws to 35 lb in, then check switch operation.

Those are probably the worst instructions I have seen in a while.
Anyway, since I was looking at doing this job soon myself, I checked which way the rod moves - in relation to the rotational direction of the lock cylinder.

If rotated CW (START) the rod moves toward the switch. And if rotated CCW...

You must be registered for see images attach

 

[CRM]

That is a lot of stuff. I have a floor shifter but I think I can still figure it out from everything you've posted. Thanks, I'll try it this weekend.