back up light switch....help!!!!!!

[wade]

i have a very confusing issue with my 72 gmc 1500 regarding the back up light switch. my problem is that the switch itself works fine,but it leaks. So no problem, just replace the switch. my issue now begins, it seems that this switch, according to over 4 parts stores and 3 transmission shops does not exist on the thm 350 transmission. I know for a fact that this is the back up light switch, because unplug switch, reverse lights dont work, plug switch back in, lights work. the switch i speak of is located right in front of the dipstick tube on the passenger side,and aft of the detent or kickdown cable. most other thm 350 that i have looked at either have this port pluged off, or on later transmissions,this
was the place they put the lock up torque converter switch. my question is how can this be!!!!! did gm come up with different reverse switches for different years, when i have ordered the so called switch from a parts store, they keep giving me the neutral safety switch that goes on the steering column. and how can the same port on the same thm 350 transmission be used for a back light switch on one and a lock up converter on the other, i wasnt even aware that the thm 350 ever had a lock up converter mated with it. so is this some wierd hatch job that exists on my tuck only
or does anyone else out there know of what i speak????

[BLACK AND BLUE 67-72]

Try asking for a third-gear switch. I belive that this is what you are referring to. Is it the switch with two wire connections between the dipstick tube and the detent cable, (downshift cable) and directly below the cooler lines? If so then that is what it should be.

[wade]

yes that is the correct switch, but what would that have to do with my reverse lights, or is that just what they called that switch,sounds goofy

[wade]

sorry, missed one point. the switch itself has three terminals on it.
although there is only on wire connected to it, it is a three pronged cap with only one active wire. what exactly does the third gear switch do, or is its only funtion on this truck to activate the reverse lights

[BLACK AND BLUE 67-72]

Well, I would say that it is for both with a 3 prong plug on it, being as you have only one wire and I suppose that is the one you unplugged, it is for the reverse lights and the other two would be for the torque converter to lock-up in third gear for direct drive. But you probably no longer have the lockup converter so the other two are no longer needed. I think that the TCC Torque-Converter-Clutch Controls were on only 80' and later 250C and 350C transmissions, originally it should of had wires inside the pan on the valve body also. More than likely your transmission is a newer model 80' or later. I hope this helps!

[wade]

it sure does, great info and thanks for the fast response

[BLACK AND BLUE 67-72]

There can also be a 2-3 pressure switch in that same hole, but I think that it only has one terminal on the switch. It senses the pressure to switch from 2-3 gear. And also a TCS (Transmission Controlled Spark) on '70-'74 models can be located in the same port also.

[BLACK AND BLUE 67-72]

No problem!! Anytime!!