gkainz

Which wire or pin holds the O/D OFF light lit when selected? My switch does select O/D OFF and ON, so it works. The O/D OFF light checks good with 12V applied to the bulb. As near as I can tell, Pin 1 could be a latch voltage to hold the light on, but not really sure. The button appears to make continuity across Pins 2 and 3 (Pin 3 is 12v+ side of O/D OFF light) but there has to be a latching relay that feeds a signal back to hold the light on?

I found a chassis wiring diagram that shows a hint, but not the whole O/D OFF circuitry. It shows 2 wires coming off the PCM, Pins C1C13 (O/W) and C3C6 (LG/O) that just say "To Overdrive Switch".

Thanks!
Greg

infidel

Can't tell you which pin it is but there is no external relay for the indicator light, the switch does it.
Switch is double pole, one set sends a ground signal to the pcm for OD the other a ground to turn on the light, positive is always at the lamp.
The positive at the switch is only used for the indicator light.
There is another positive at the switch for the the illumination lamp when you have the headlights on but that runs off the dimmer circuit.

gkainz

That's what I originally thought as well about the switch, but unless the old one and the new one are both mechanically broken, both of these switches operate like a momentary contact switch.

Pushing the button in makes between pins 2 and 3 and releasing it breaks the connection between 2 and 3.

OD OFF light is wired between pins 3 and 5
Panel dash light is wired between 2 and 4

I didn't find pin 1 corresponding to anything else ... however, this was all metering the switch out of the vehicle, so I haven't (yet) looked at the truck to see what I find metering the plug yet.

gkainz

so it looks like I have a fault in the PCM? ... the wire from ground side of the OD Off light checks good all the way from the OD OFF Switch to the PCM. Since it does what it's supposed to (turns OD off) and just won't light the OD OFF lamp, I guess I'll just drive the darn thing as-is. I just hate stuff that doesn't work right, tho ...

Edit - can anyone explain the signal path back from the tranny to the PCM to that sets the ground to turn on the O/D OFF light?