General Ground Distribution Schematic
 

I found this in a another post..."Where is the ground for the TCCM? Is it with all of the other grounds under the passenger carpet?" My TCCM is completing both 4hi and 4lo circuits to ground, illuminating both the 4hi and 4lo lights at the same time. I wanted to check the various ground locations that are accessible, by i cant seem to locate a ground distribution schematic. The heater core was bad and leaked coolant all over the pass side floor, fluid still trapped under carpet. Could thid be affecting the ground in this location, if there is one? 2-button Switch on dash is ok, checked the plug to the switch and there is power on all circuits back to the TCCM, showing me that the TCCM is grounding all 4wd indicator light circuits and the momentary switch circuits to engage 4wd. I will also try to disconnect the feed from the dash switch to the TCCM and check for continuity to ground on the various wires, but the lights arent always on, just when you engage 4hi or 4lo. Any ideas why both 4hi and lo engagement circuits and indicator light circuits would have power at the same time? Thanks in advance guys(and gals:)).

I am interested in this as well. I have been having a few dash electrical problems on my 1991...I figure it probably a bad ground...wish I knew exactly where to look.

HHimmy...I just re-read your post. Is there a grounding bus underneath the passenger carpet? Have you seen that?

No i havent seen anything yet under the pass side carpet, but i have been told the 1st gens have a ground located on the frame rail near the radiator supports on the frame rail, but i havent tracked it down yet. But the 2button switch could still be a problem. When the switch is pushed, it completes the circuit to the TCCM momentarily, the TCCM then grounds the circuit, the power is at the switch. Right now, for some reason, both circuits in the switch are being momentarily completed, letting the TCCM allow both circuits to complete to ground, hense both lights being on at the same time. Perhaps....the switch in completing BOTH circuits momentarily when only one should be? Ill try to track a 2button down, noone but GM appears to have it (besides the boneyard).

Quick update: Checked dash 2button again, worked the switch back and forth, re-installed and WOW, works perfect! Im assuming the contacts inside were a little corroded due to the previous owners lack of use, only time will tell.

Hope it works out! I am not sure if the old switches can be dismantled, but if it comes back, you could try and disassemble and clean it. If that does not work, then just replace it.

Fingers crossed...thanks again, Kyle for all the help. This forum is filled with excellent information on s-series vehicles. I plan to keep this vehicle on the road as long as possible, so i will be checking in frequently!!!