I have a dual bolt pattern bellhousing TH-350 from a 1980 Pontiac Catalina. On the left side of the trans above the pan rail it has a connection with 2 wires. I don't remember seeing this on older TH-350s. Does anyone know what it is for?

 

That is the connection for the torque converter clutch, that is found on most 80 & up transmissions.

 

You have a th350-C. You could hook a switch to it to control the lock-up.

 

Would it hurt the trans to not use it? Or, in order to use it, could I just wire a toggle switch? Is one of the wires a ground? Are the 1980 and up TH-350s any better or worse than the older ones? I never knew they made a lock-up type TH-350. That might be better for highway gas mileage.

 

unless i am mistaken one of the wires is for the lock up and one is for a temp sensor...that was to allow your tranny and engine to warm to proper temps before locking up...and yes you can control the lockup with a toggle switch...

 

One wire is ground, one is 12V positive. Both needed to pop the solenoid that locks the converter. You will put extra heat in the tranny if you don't lock it up, probably OK if you run a cooler--but I still would hook it up. I've heard that sometimes they are wired through a temp sensor to not allow lock-up when cold. Really doesn't hurt anything to lock when the engine is cold though. None of the aftermarket lock-up kits use any kind of temp sensor. On some the computer locks and unlocks the torque converter.

 

To my knowledge , contrary to the 700r4, running a TH350C without lockup will not harm the transmission.
It will hurt your wallet dough...milage will suffer.
You need break + ported vacuum switches to control lockup properly.