Hello All - So i replaced my engine harness(to HEI and higher amp alternator) and I have one plug that i'm not sure where it goes. It is close to the plug on the firewall. It doesn't seem to be on the old harness. Attached are pictures of the plug and the wiring diagram showing its for N.C. Press Switch and Down Shift Sol. Can you please tell me where it goes? Thanks in advance.

 

Looks like the brake warning wire from here. Should plug into the prop valve.

 

x2

 

If that rubber boot has two wires (hard to tell from the angle in your photo) that is the transmission kickdown plug. The kickdown pigtail is built into every harness, whether the car had a TH400 or not. The two wires are one for kickdown signal and one for the pressure switch used with the Transmission Controlled Spark system. The brake warning light pigtail has a single brown wire and a round connector molded into the rubber boot.

 

Yes, it has 2 wires, one black and one black with an orange stripe. Is this plug used on a TH350? which is what I have. Thanks again Joe

 

In prior years, this pigtail was just taped up in the harness if it wasn't needed. For the 1970-72 model years, this connector was used with every transmission (even manual) due to the Transmission Controlled Spark system. The black/orange wire is the kickdown, which is not used on other transmissions, but the wire for the TCS switch was used on all of them. Your TH350 trans should have a pressure switch on the side if it is the original one from your car. If it's ever been replaced, that switch might not be present.




The switch will be located on the passenger side of the trans, below the cooler lines.

 

Very helpful, thanks so much!