Can't turn off O/D?
 

I know the light isn't blown out since it turns on when I turn the key, yet when I hit the button on the shifter it doesn't go off. Any ideas?

Assuming the PCM hasn't failed, you've got either a bad button or loss of continuity from the button to the PCM. If memory serves, the button merely provides a momentary ground to an input of the PCM, which the PCM reacts to by toggling the overdrive state.

Grab the factory service manual that's found in the 2nd gen FAQ section, and puzzle out the circuit. Probe at the PCM end first because it's easiest to get to -- if that pin doesn't fall to ground when the button is depressed, you're off to the races with a repeatable symptom. Just to confirm, carefully ground that pin to observe that the light goes off and on when you repeatedly apply the ground. I'm guessing it will.

From there, it's a button, a wire, or a connector pin and just a matter of figuring out which.

This sounds like fun! NOT! LOL ... :icon_no:

I looked in the manual and I have NO idea what I am looking at. Does anyone have any hints? I'll probably start at the switch and trace it from there ... I don't want to go and blow up my PCM cause I am an electrical nitwit.

im having the same problem with my o/d switch.

at first it would turn off after pressing and releasing it several times, but then i couldnt get it to back on unless i turned off the truck.

nowadays i dont even mess with it

but if you figure it out make sure you tell us what it was

Ok, overdrive switch just grounds a circuit, that the PCM pays attention to. Looking at the switch, it looks like a four pin.... but, the wiring diagram only shows two... not sure what that is all about.

Basically, the PCM sends power to the switch. When you press the switch, it completes the circuit, grounding it. PCM sees current flow there, and disables overdrive. Extremely simple circuit......

To test, pull the little cover off of the end of the gearshift lever, pull the switch out a little bit, pay attention to how it is hooked up..... and pull the switch off. On the connector side, with the ignition on, should be power on one side, (might have to have the engine running for this test, to avoid ASD event.... not sure....) and the other side should have continuity to ground. If both of those are true, replace the switch.

Well, I went a little different way about it. When I pulled the switch off I checked for continuity on the switch, and it's there. Any other ideas? I don't want to manually test it by plugging stuff into the back of the connectors at the PCM, that just sounds like a recipe for disaster ...

Check and see that you have voltage on one wire, and continuity to ground on the other at the connector for the button. If you are missing either one, O/D off won't work.