I know this is a common Problem on these trucks so here is what Ive done so far. First my truck is a 2000 model, 4.6 auto, 4x4 with 116,000 miles on it. Ive had the truck for 5yrs and never been able to turn the overdrive off. I pulled the gear shifter out and replaced it with a new ford unit bc the wires had bare spots in the old one. I checked the 5amp fuse which is good. I still couldnt turn the overdrive off. I checked to see if I had power to the fuse and I do not have power going to the 5amp fuse for the overdrive. I checked what wires I could see on the trans and everything is hooked up. Is there a wiring diagram to tell me where the O/D wire hooks up. Have any of you guys ran in to this before. Ford wants $85 to look at it but Ive got alot of help in the 73-79 section here on this site so hopefully you guys can help me out some to. I checked every fuse in my truck and the 5amp O/D fuse is the only one with no power to it. Thanks for and help. Scott

 

The switch actually does two things.
1 it signals the PCM with separate contacts to inhibit OD on separate leads to the PCM.
2 the switch turns on the lamp by switching power to the lamp..
Two separate functions.
None of this goes directly to the transmission because it's fully under the control of the PCM.
Are you sure the OD in not being inhibited by watching the Tach RPM rise when the switch is operated whether the lamp comes on or not?
Good luck.

 

Yes im sure the O/D isnt getting turned off. Im not getting power the the 5amp fuse. First I thought the fuse was the problem but it is good bc there is no power to it. I dont know much on how the system works or what tells what to do thats why I hated to mess with it. But Ive been pulling a trailer around some lately and need to turn it off from time to time. I'll see what I can read up on tomorrow evening. Im going to get a book on these trucks and do some reading. Thanks

 

The switch actually doesn't turn on the TCIL directly, a signal from the PCM does that. The switch is only an input to the PCM.

If you don't have power to the fuse that supplies the switch (F29), of course it will never work.