On my 1992 chevy truck 700r4 transmission, what should the factory pressure switch be? Normally Open or Normally Closed? Mine went out, I replaced it with one that I had and I think that it has the wrong polarity. Now I get High Gear signal to the ECM in all Forward gears except OD. I guess is screwed up! Just trying to find out the correct part and possibly number before I go to the dealership for another one. I spoke with them on the phone and they wanted to know which it was? I honestly didn't check and can't without pulling the pan. When I pull the pan I want to have the switch. I am pretty sure it is normally open but want to double check.

 

a lot of that depends on how the valve body is wired and how many switches it has. some switches have one post and some have two. but i'm not sure which is normally open or closed. can the dealer match it up with the original? the atsg book shows 15 different ways it could be wired. your best bet would probably be to go ahead and drop the pan and go from there.

 

Mine has one switch with two post on it and the TCC solenoid controlled by the ECM.

 

that narrows it down to 4 diagrams. how do the wires run? how many wires go from the case connector to the switch?

 

One wire only. The other wire runs to a ground on the Valve body. Maybe it should have had a single pin switch in it? The transmission has had a dual pin for as long as I have owned it.

 

so only one pin on the switch is used? if so i need to know how each wire is ran. start from connector to where?

 

Pin A is +12VDC from the brake pedal switch to the solenoid
Pin B is from the switch to the ECM and is grounding the ECM(at unknown times)
Pin D is from the ECM to the solenoid and have to assume it operates the lockup.

 

Most applications use a N.O. 4th gear switch, but most thirdgens use a N.C. switch. Try an 8642473 for a single terminal N.O. switch or 863433 for a two terminal N.O. switch.

 

pin d is how the ecm actually grounds the solenoid. there is only one diagram that has one wire going to the switch and it is normally closed. it is a one terminal switch. has the tranny been rebuilt before? this is according to the diagram.

 

I think the one that is in there is a N.O. Probably from my original 1983 700R4. I am almost certain it was rebuilt before I got it at some point. Then I rebuilt it. Worked good until I swapped the switch. Guess I am pulling the pan on this one, the just get a new one. Got the part # for the normally closed switch (opens with pressure right?). Thanks for the help, Chris.

 

A normally closed switch opens with pressure. The ECM will be grounded in all gears except 4th.

N.C. switches are 8634475 or 8642569 for single terminal, 8642346 for two terminal.

 

I'm a dummy, just realized I could take my DVOM and check the continuity in the switch. NO or NC all from the outside of the case. The one wire will fit into the same hole as the two wire I am assuming. Get the opposite self-grounding switch 5 qts of fluid and go from there.

 

Yeah they're all 1/8 NPT.