Transmission wiring

Mr.Buick

New Member
Joined
Feb 1, 2002
I am installing a new transmission and the new one has only three wires to the electrical plug on the side of the case, but my old transmission has four. I looked in my transmission book and the wiring diagram shows three wires, so my question is why does my old transmission have four? The diagram shows 1-Solenoid assemby, 2- Pressure switch, 3- Temperature switch
What will happen if I plug into the three wire with my four wire connector? thanks in advance
 
3 wire trans ----

I have a 3 wire trans in my 84tt (4 wire BQ was changed out before I got car)--It works fine,,the 4th wire is for 3rd gear shift solinoid,controled by ECM, Now (with a 3 wire),3rd shifts automaticly,via the VB,and how its calibrated. This was explained to me by a trans shop,here in AZ,so I `ll take it as correct . But yes,I`m living proof that a 3 wire does work in a turbo car.
 
the trans shop didnt tell you the truth .there is one wire with 12 volts to power the solenoid,1 wire which tells the computer the transmission is in third gear,1 wire that tells the computer you are in fourth gear ,and 1 wire which grounds the solenoid based to introduce lockup based on the ecm strategy and operating conditions while in third or fourth.a 3 wire setup will only lock the convertor in fourth as the ecm wont recieve the "I AM IN THIRD GEAR SIGNAL"thru the missing wire.this works great imo.the only thing is a car with a 4 wire connector in the vehicle wiring harness to the transmission wont plug onto a 3 pin connector on the case.you must use the original 4 pin case connector with the 3 wire 3rd gear lockup info delete harness.
 
OK if I switch the plug on the case so the 4 wire conector will fit and only plug in the 3 wire plug on the inside of the transmission I loose the 3 gear lockup? The 4th wire will now not connect to anything on the transmission, but will that mess up the computer?
 
I don't think this has anything to do with the wiring, but when I took it out for a ride the transmission seems to be stuck in high gear when it is in drive. After I got on the hwy and came to a stop it acted just like it was trying to take off in high gear. I had to manually shift into low to go. Could it be that the converter is locked up? What tests can I do to diagnose the problems.
 
Take that back, It appears that the converter was locked up at idle. I unplugged the electrical wiring to the case plug and the transmission seems to be working ok now. I went for a ride in drive and the transmission down shifts and up shifts ok now, so it must have gotten the signal to lock up and didn't get the signal to release the lock up. could this be because the wire is missing for 3rd? The old 4 wire transmission never had this issue.
 
OK what would you suggest as my next move? I need to diagnose the problem so I can figure out what to do. I can really feel the difference in the high stall torque converter when I apply the gas. I could put a switch in the wiring and only turn it on when I get to hwy speeds?
 
Originally posted by chris718
the trans shop didnt tell you the truth .there is one wire with 12 volts to power the solenoid,1 wire which tells the computer the transmission is in third gear,1 wire that tells the computer you are in fourth gear ,and 1 wire which grounds the solenoid based to introduce lockup based on the ecm strategy and operating conditions while in third or fourth.a 3 wire setup will only lock the convertor in fourth as the ecm wont recieve the "I AM IN THIRD GEAR SIGNAL"thru the missing wire.this works great imo.the only thing is a car with a 4 wire connector in the vehicle wiring harness to the transmission wont plug onto a 3 pin connector on the case.you must use the original 4 pin case connector with the 3 wire 3rd gear lockup info delete harness.

Do you happen to know what ones are what? IE: If you were looking at the trans from the side of the connector.. what wires do what? I'm looking to tap in to that plug for the torque converter nonlock up. Or should I just tap in behind the plug in the car for the computer and if so what wire there? Thanks for any help on this!
 
According to the schematics, looking at the plug on the transmission with the tab on the left.
Top left = +12v
Bottom left = ECM ground to TCC solenoid
upper right = ECM
lower right = not used
 
I disconnected the plug and it seems to be shifting good, but I have no lock up now. I was thinking of putting a switch in the ground lead so I could manually turn it on when on the Hwy. Let me know if that's a good idea?
 
Originally posted by Mr.Buick
I disconnected the plug and it seems to be shifting good, but I have no lock up now. I was thinking of putting a switch in the ground lead so I could manually turn it on when on the Hwy. Let me know if that's a good idea?

I'm in the same boat as you. My old trans was searching and shifting sloppy, Had it rebuilt but had the same issues. Unplugged it and it was fine but no lock up. So I'm going to replace the solenoid sometime soon and put a switch in so I can manually work it. Then I'll have the best of both worlds! :)
 
Can I add the fourth wire to an OE 3 wire trans?
If so what is needed for this?

If you unplug the trans how does the computer control timing and boost per gear?
 
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