'70 TH400 TCS Trans Switch??

[Carr C.]

I have a 1970 LS5 Corvette with a TH400 automatic. I'm converting it back from a 4-speed for judging.

The new wire harness (Lectric Limited) and the wiring diagram (Doc Rebuild) have a perpendicular ( -I ) two prong connector that goes to the transmission (Auto Transmission TCS Switch).

I cannot find enough information in the AM to figure out where it goes on the driver's side of the transmission, but I do have a single prong connector sticking out towards the left rear of the pan behind the shift linkage.

I have looked in the Corvette catalogs but what I'm seeing doesn't look right.

Where does it go and where do I find a switch with the right 2 prong connector?

Thanks!

[Harmon C.]

Re: '70 TH400 TCS Trans Switch??

The single prong wire on the transmission was for the switch on the gas pedal on a 73. The two prong plug went to the switch on the four speed linkage for the backup lights and on an automatic the same wire was pulled back through the firewall and the connection was near the shift lever inside the car on an automatic. This is 73 information so a 70 may be different but it may help.

[Patrick H.]

Re: '70 TH400 TCS Trans Switch??

Carr,


I'll be interested as well to hear from those with 70s and THM 400's.

Why?

My 70 Cutlass also has a "T" shaped female connector on the wiring harness and a one-prong male connector at the end of the switch on the transmission. GM did make both kinds of male connectors on these switches over the years (single prong and dual "T" prong), but from what I can tell on my car (which may or may not mean anything) the single prong / dual hole plug is correct.

Patrick

[Joe L.]

Re: '70 TH400 TCS Trans Switch??

I have a 1970 LS5 Corvette with a TH400 automatic. I'm converting it back from a 4-speed for judging.

The new wire harness (Lectric Limited) and the wiring diagram (Doc Rebuild) have a perpendicular ( -I ) two prong connector that goes to the transmission (Auto Transmission TCS Switch).

I cannot find enough information in the AM to figure out where it goes on the driver's side of the transmission, but I do have a single prong connector sticking out towards the left rear of the pan behind the shift linkage.

I have looked in the Corvette catalogs but what I'm seeing doesn't look right.

Where does it go and where do I find a switch with the right 2 prong connector?

Thanks!

Carr------


The TCS trans switch is right where you found the single prong connector----on the left side, right above the rear of the pan. My recollection is that this switch uses a single prong connector and not a dual prong.

By the way, did you ever find an interlock cable bracket for the transmission?

[Carr C.]

Re: '70 TH400 TCS Trans Switch??

I have discovered that all 70 TH400's with a TCS system (not just Corvettes) had a 2 prong T shaped male transmission switch. One prong is for the kickdown, and the other is for the TCS system.

I need to know a part # for the 2 prong T-shaped male connecter in the side of the transmission, or better yet where to find one, and then what went with it inside the transmission.

This is a tough one!

Any help would be greatly appreciated!

[D S.]

Re: '70 TH400 TCS Trans Switch??

Carr, Eddie Wascavage rebuilds Muncies and may know and/or have what you are looking for. Call him at home at 1-610-566-7107 or cell 1-610-842-1190.

Scott

[Joe L.]

Re: '70 TH400 TCS Trans Switch??

I have discovered that all 70 TH400's with a TCS system (not just Corvettes) had a 2 prong T shaped male transmission switch. One prong is for the kickdown, and the other is for the TCS system.

I need to know a part # for the 2 prong T-shaped male connecter in the side of the transmission, or better yet where to find one, and then what went with it inside the transmission.

This is a tough one!

Any help would be greatly appreciated!

Carr-----


Yes, it could very well be that the automatic used a 2 prong plug. I was thinking of the manual trans switches---they used a single prong plug.

I think what you're referring to as a "connector" is actually the switch, itself. I believe the switch threads into the transmission case and the terminal is an integral part of the switch. The connector on the wiring harness then plugs into the terminal on the switch.

You can still purchase this switch from GM. It's undergone several part number supercessions and it's likely the current switch is not configured exactly like the original. However, I would not think that it could be very much different. The part number is GM #8683502 and it sells for about 13 bucks, GM list.

[Joe L.]

Re: '70 TH400 TCS Trans Switch??

The TH400 With TCS has a two wire connector on the drivers side of the case. It is a "pass-through" connector with male spade terminals on both the inside, and outside of the nylon. It seals in the case with an o-ring, and has locking tabs. edit: see next post for a source

Inside the trans, the kick down solenoid connects to one of the terminals. (I can't remember which one, but it corresponds to the orange wire in the vehichle harness).

There is a N.O. pressure switch screwed into the end of the valve-body. It is an 1/8MPT with a 'button' electrical connector. The location on the VB is a direct clutch (3rd gear) pressure tap. Then a jumper wire goes from the switch to the other terminal on the pass-through connector. The TCS switch corresponds with the black wire in the vehichle harness.

I don't know what the P/N Joe describes above is. It may be for the TH350 that has an external switch that looks like an engine oil pressure light sender, which is kind of what it sounds like. But the TH350 is NOT the same as the TH400 set up.

Hope this is what you were looking for.
Dave

Dave------


The original TCS switch used for 1970 Corvettes with M-40 (i.e. THM-400) was GM #6462286. I am 100% certain of that.

The 6462286 was discontinued from SERVICE in August, 1985 and replaced, successively, by GM #25036207, GM #8634475, and, finally (to date), GM #8683502.

Were the supercessions correct? That I do not know as I have no personal familiarity with any of them. All I can say is that is what GM says is the correct current replacement. Having researched it a bit further, there are certain "irregularities" in the "pedigree" of the 8683502. For one thing, it's a group 4.265 part, not the 4.075 I would expect. For another thing, one of the predecessors, GM #8634475, is shown as also having THM-700 applications, but not for the TCS switch application. This gives me reason to wonder.

In any event, the GM #8683502 is the switch that GM says is the current SERVICE replacement for the 1970 TCS switch application. It's extremely rare that they're incorrect on something like this, but it does happen. This could be one of those times.

[Joe L.]

Re: '70 TH400 TCS Trans Switch??

To add a little to this, while earlier AIM's appear to be "silent" on the issue of the location of the TCS switch for auto trans applications, the 1973 AIM does provide such information. In 1973 the THM-400 was still the only automatic transmission being used in Corvettes. So, unless the location of the TCS switch changed between 1970 and 1973, I would think that this 1973 information would be applicable to 1970, as well.

However, apparently the TCS switch did change between 1970-72 and 1973. The original 1973 switch was GM #8627332 and that switch is still available today from GM for about 28 bucks, GM list.

Attached is an excerpt of the 1973 AIM.

[Joe L.]

Re: '70 TH400 TCS Trans Switch??

I have a 1970 LS5 Corvette with a TH400 automatic. I'm converting it back from a 4-speed for judging.

The new wire harness (Lectric Limited) and the wiring diagram (Doc Rebuild) have a perpendicular ( -I ) two prong connector that goes to the transmission (Auto Transmission TCS Switch).

I cannot find enough information in the AM to figure out where it goes on the driver's side of the transmission, but I do have a single prong connector sticking out towards the left rear of the pan behind the shift linkage.

I have looked in the Corvette catalogs but what I'm seeing doesn't look right.

Where does it go and where do I find a switch with the right 2 prong connector?

Thanks!

Carr------


I was incorrect regarding the TCS switch installing by threading in from outside the transmission. The switch is installed inside the transmission as others have pointed out. Also, I did some more research on this and there is, apparently, a connector mounted on the outside of the transmission as you describe. This is NOT the connector on the wiring harness pigtail, but one on the transmission, itself.

GM says that the part number for the SWITCH is just as I described earlier---GM #8683502. Whether, or not, this is the correct part, I cannot say, for sure. However, it is the one that's the "direct descendant" of the original switch. Since it's internal to the transmission, that also might explain why I find it now in group 4.265.

The current part number for the CONNECTOR you seek is GM #8629502. Once again, I don't know if this is correct, but it's the part that GM says is the "direct descendant" of the original. It's still available from GM for about 16 bucks, GM list.