I’ve got a 1989 f250 4x4 with the 7.3 idi non turbo. I’m having some transmission/electrical issues. My truck was over charging at around 17 v, obviously frying my batteries but at the moment it’s my daily. So I continued to drive it until I was able to get a new voltage reg, but before I got one I decided it would be a good idea to unhook the batteries so they wouldn’t over charge while driving. Not thinking the batteries were the only thing stopping that 17v from being sent through my electrical. As soon as it happened I smelt electrical, so I shut the truck down and hooked them back up but it was two late. The OV light will not go out, the tack went out, and the transmission will not shift on its own, seems to be stuck in third. I replaced the voltage reg and checked all the fuses under the steering wheel. Did not find any blown and I have power to all of them except the clock fuse. I was wonder if anyone would have any suggestions or schematics that would be possibly useful to get the transmission shifting again. I was told to look for a melted wire going to the transmission, and that it could possibly be the computer putting it self into limp mode until I’ll the problems solved, also tested the alternator it does work,thank you.

 

[QUOTE=1989browntown;20400180]I’ve got a 1989 f250 4x4 with the 7.3 idi non turbo. I’m having some transmission/electrical issues. My truck was over charging at around 17 v, obviously frying my batteries but at the moment it’s my daily. So I continued to drive it until I was able to get a new voltage reg, but before I got one I decided it would be a good idea to unhook the batteries so they wouldn’t over charge while driving. Not thinking the batteries were the only thing stopping that 17v from being sent through my electrical. As soon as it happened I smelt electrical, so I shut the truck down and hooked them back up but it was two late. The OV light will not go out, the tack went out, and the transmission will not shift on its own, seems to be stuck in third. I replaced the voltage reg and checked all the fuses under the steering wheel. Did not find any blown and I have power to all of them except the clock fuse. I was wonder if anyone would have any suggestions or schematics that would be possibly useful to get the transmission shifting again. I was told to look for a melted wire going to the transmission, and that it could possibly be the computer putting it self into limp mode until I’ll the problems solved. Also the voltage gauge is bouncing around between 13-15 and the battery light flickers sometimes, thank you

 

The first thing you need to do is fix your alternator. It should charge at 13.8-14.7V at idle. You can remove the alternator and have it tested at the auto parts store or they can test it on the vehicle.