95 6.5 Tranny Problem

[96TD2500]

There is a relay spliced into the trans harness under the truck and I don't know why. The truck will not shift sometimes, then sometimes will shift fine. Other times it will jump in and out of OD...other times it will not go into OD at all. I'm trying to figure this one out. Hopefully someone here can help out some.

[gmctd]

Possibly someone's attempt to provide manual TCC lockup - remove it and splice the color-coded wires back together

[96TD2500]

The wire is not cut, it is tapped into, then run up to a relay on the firewall. A wire runs into the cab from the relay also. Sometimes the truck shifts great other times it will not shift at all... My 96 doesn't have this problem at all....but this 95 is going crazy. Thanks for your help so far.

[damork]

I have a 95 and had problems that you describe with lockup going in and out. I also experienced a strange off the line delay (may or may not be related), so went back to the basics and looked for electrical problems.

I posted about this problem back in 04 and someone recommended looking into the trailer wiring harness as well as doublechecking the vehicle grounds all around the truck. It turned out my trailer wiring plug wiring connections were a mess and I needed a completely new plug. I changed it, coated all new connections with a sealer, and proceeded to clean every chassis ground I could find on the truck.

That corrected the problem.

Now - with respect to your wire under your truck, it may be an added relay to provide better power to your transmission than what comes through the ignition switch. There are kits for sale out there that cost about $60 or you can buy a Bosch relay with wire/connectors for under $10 and do the same thing which is what I did. I simply broke into the harness to feed 12V to the transmission just outside of where the plug connects to it on the drivers side, (make sure you follow proper wiring practices and include proper fuse, turn it on with the ignition switch, etc).

With respect to strange or delayed starts off the line (hesitate on upshift or strange engagement), pull the speed sensors and check for gunk buildup on the magnetic tip and clean it off. It fixed the problem I had and was something I learned from a Humvee website.