67-70 TH400 Kickdown Harness Firewall Hole Location

[pjmoreland]

Does anyone have a photo that shows the stock location on the firewall where the TH400 kickdown harness passes through on a 67-70 truck?

My '68 has a TH400 that the PO installed, but he did not install a kickdown switch. I've purchased a 67-70 kickdown harness from GMCPauls, along with a B&M switch that I will mount to the TH350-style kickdown bracket currently on my engine. I will have to drill a hole in the firewall, and I'd like to put it in the stock location.

I searched through many threads about TH400 kickdown switches, and the closest I came to a photo was in this post, although it was a bit vague.

https://67-72chevytrucks.com/vboard/...firewall+th400

[72c20customcamper]

My kickdown solenoid wires run down under the coil and to the trans . Dont see them going into the firewall but I could be missing them

[pjmoreland]

Originally Posted by 72c20customcamper

My kickdown solenoid wires run down under the coil and to the trans . Dont see them going into the firewall but I could be missing them

Thanks for the photo. The harness I bought has a grommet molded onto it for the firewall. My understanding is that it gets power from one of the switched ignition prongs on the fuse panel.

[72c20customcamper]

I'll look at it again tomorrow

[pjmoreland]

Originally Posted by 72c20customcamper

I'll look at it again tomorrow

Thank you!

[FirstOwner69]

I believe 72c20customcamper is correct. Here are a couple pictures from my truck that may help. The first pic shows the original TH400 switch with the wiring coiled. The plug on the end attaches to the transmission. Are you confusing the plug with a grommet?

[pjmoreland]

Originally Posted by FirstOwner69

I believe 72c20customcamper is correct. Here are a couple pictures from my truck that may help. The first pic shows the original TH400 switch with the wiring coiled. The plug on the end attaches to the transmission. Are you confusing the plug with a grommet?

Here's' a photo of the harness I bought, with the following features:

1) Power connector with a pink wire that plugs into the fuse panel. It has a piggyback connector in case something else needs to be plugged into the same spot on the fuse panel.

2) Firewall grommet

3) Carburetor switch connectors

4) Transmission connector with rubber hood

The power connector 1) is very close to the grommet 2), so I'm thinking the firewall hole has to be close to the fuse panel. The mystery pink wire in the link I included in my original post is right over by the fuse panel.

[dmjlambert]

Here is where it goes through the firewall.

[pjmoreland]

Originally Posted by dmjlambert

Here is where it goes through the firewall.

Awesome. Thank you!

[FirstOwner69]

GMCPauls site shows that the 67/68 harness is different from the 69/70 version. However, his pictures look the be the same. Neither resembles my "69 original.

EDIT: I believe some TH400s had a one prong connector on the transmission and others had two. I don't know when the change was made.

[pjmoreland]

Originally Posted by FirstOwner69

GMCPauls site shows that the 67/68 harness is different from the 69/70 version. However, his pictures look the be the same. Neither resembles my "69 original.

Oops, ok. I made the incorrect assumption that 67-70 were the same. There are lots of threads about the 71-72 style where the switch is mounted inside the cab on the gas pedal linkage.

[pjmoreland]

Originally Posted by dmjlambert

Here is where it goes through the firewall.

Is the truck in that photo a 67? The fuse panel is sideways.

[chewychevy67]

My 67 gets power from the wiper switch ( it has a jumper harness from the wiper terminals) and goes thru the firewall by the Throttle.

[FirstOwner69]

Originally Posted by pjmoreland

Oops, ok. I made the incorrect assumption that 67-70 were the same. There are lots of threads about the 71-72 style where the switch is mounted inside the cab on the gas pedal linkage.

Did you see my edit to my last post with a possible reason for a difference?

[dmjlambert]

Are you especially interested in drilling a hole? I didn't understand why Chevy didn't just push an extra Packard 56 terminal into the firewall connector. I've put extra wires through the firewall just by using empty slots in the firewall connector.

[pjmoreland]

Originally Posted by FirstOwner69

Did you see my edit to my last post with a possible reason for a difference?

Oh, I missed that. Interesting. It makes sense to have it exit closer to the carb and transmission.

[dmjlambert]

Originally Posted by pjmoreland

Is the truck in that photo a 67? The fuse panel is sideways.

The picture is from my 1969 CST/10. In the picture, the left half of the firewall connector is for the engine harness, and right half is the headlight harness. The fuse panel is a separate item inside. I removed the fuse panel to gain access to the back of the firewall connector, and insert my extra wires and terminals, then put the fuse panel back.

[pjmoreland]

Originally Posted by dmjlambert

Are you especially interested in drilling a hole? I didn't understand why Chevy didn't just push an extra Packard 56 terminal into the firewall connector. I've put extra wires through the firewall just by using empty slots in the firewall connector.

That's a very good idea. I'm in the middle of an idiot light to gauges conversion and will be routing the black and black/white ammeter wires through the firewall connector per the factory wiring. There are six unused spots still, so I'll do that. It will be much cleaner. I'm trying to stay away from running random wires through random holes so that it looks tidy.

[pjmoreland]

The following thread shows the stock firewall hole location for the kickdown power wire in a 1968 with a TH400.

https://67-72chevytrucks.com/vboard/...d.php?t=825672

[HO455]

Here are 2 poor photos of where the T400 kick down wire passes through the firewall on my 67 Burban. It is the yellow wire at the end of the arrow.
The PO converted the throttle from a rod to a later model cable hence the round plug above the kick down wire. Pay no attention to the PO's cobbled up mounting of the kick down switch.

[pjmoreland]

Originally Posted by HO455

Here are 2 poor photos of where the T400 kick down wire passes through the firewall on my 67 Burban. It is the yellow wire at the end of the arrow.
The PO converted the throttle from a rod to a later model cable hence the round plug above the kick down wire. Pay no attention to the PO's cobbled up mounting of the kick down switch.

GM sure moved that wire around a lot through the years. Does the wire on your 67 Burban get power from the wiper switch like chewychevy mentioned in post #13?

[HO455]

Unfortunately the truck is back in the body shop and my memory has failed me on this. It may be next week before I can verify it for you.

[pjmoreland]

Originally Posted by HO455

Unfortunately the truck is back in the body shop and my memory has failed me on this. It may be next week before I can verify it for you.

No rush at all. I'm just curious.