Ok guys I have read several threads on this site and others, and I'm still stumped. I have a 1992 d350 . I was driving down the road and it dropped from 4th to 3rd and will not change back. I checked the voltage on the TPS and it was good with no flat spots, and it has a new VSS. I also bypassed the temp sensor on the trans line, and still no luck. I've read that it could be the OD solenoid but I don't know where it's located or how to test it. Any help would be great.

 

First,

Check all the wiring, I have seen where there wires that run on top of the trans gets pinched and then it cannot shift into OD, the Solenoid is inside the trans pan.

 

The od solinoid is controled by the computer inside the drivers side fender. The throttle position sensor sends a signal to the computer along with the speed sensor on the tranny. It is "switched on the ground side of the solinoid. You should have 12volts to the solinoid at all times with the ignition switch turned to run. Grounding the ground wire will engage the OD. I drove around with a temporary switch in this manner for a while until I could fix the real problem that I had which was in the wiring.

 

Well today I pulled all the wire looms off the harness going to the transmission ,and it looks like at one point in time some one drove the truck a few miles with the wires dragging the asphalt. I have never seen such a darn mess and I'm pretty sure that my problem lies there. Do you know of anywhere that I could get that piece of the wiring harness or would I be better off just wiring in some new ones

 

I'd just run some new wires and solder them into the connector.

 

Do one of the electrical plugs on the transmission go to the OD solenoid if so which one do I apply 12 volts to make the OD kick in. Thanks in advance.

 

Wire gauge and color code are on the diagram.

Diagram is from the factory FSM. Get it at Jeno's on Cd for 'bout $30. You'll sleep with it.