Problems replacing ignition switch on 75 D100

The old ignition switch for the truck won't run accessories when the key is in the run position (when it's cold out) so I set out to replace the ignition switch as well as the broken turn signal cam.

When I pulled the old switch out and compared it to the new switch, they're pretty similar except the colors are different and the terminals go into different spots on the back of the switch so it's not like I could just look at it and figure it out. According to the schematic, the plug under the dash is as described from left to right:

Starter Relay - Orange (.15v)
Accessories - Light Blue (0v)
Ignition Run - Red (0v)
Ignition Starter - Pink (0v)
Battery - Black (12v)
Ground - Blue/White stripe (0v)


Now in reality when I'm looking at the plug there are 5 pins on the right side of it. Two blank spots and then a pin on the left which I'm guessing connects to the orange wire on the column to light up the shifter display. The original switch has the Blue/White striped wire connected to it but there's no pin in the connector so it was essentially connected to nothing. I can't find evidence of there ever being a wire there when looking at the factory harness under the dash. I also tested for voltage which you can see above.

So I grabbed a multi meter and checked continuity with the switch in all 3 positions.

Old switch:

Acc: Black - Light Blue

Start: Black - Orange - Pink

Run: Black - Red - Light Blue

Everything seems to be working fine. I did this when it was warmer and the light blue wire (accessories) had continuity in the Run position. When the switch is cold there is no continuity there for whatever reason.

So I took the new switch and tested it's continuity so I could figure out the color pattern.

New Switch

Acc: Nothing (possible problem right out of the box)

Start: Red - Brown - Yellow

Run: Red - Black - Blue

Since Red appears in both Start and Run, I'm guessing the new switch is going to use Red as the 12v source while the old switch used to use Black as the source.

Reconnected the wires to the connector and when I was done I ended up with what you see in this picture.



I plugged it back in and when I turned the switch, not a single thing happened. I figured maybe I had the wires wrong. So just to test, I took the old switch, plugged it back in and when I turned the switch, nothing happened either. I'm not sure if I'm now chasing two separate problems at this point because there's no reason why the old switch wouldn't bump the starter over. I know this is a ton of information but I tried to give all I could. Does anyone know where I can start on this?

If red is the battery wire, it should have continuity to "something" in all positions except off and lock.

Seems like you are on the right track with continuity.

You should be able to probe the connector when installed, and test for "start" voltage. You sure you did not screw up the shift linkage, moving the column, etc? (Automatic? Clutch switch?)

What exactly does / does not work at this time?

Doh! I moved the column sleeve and shifter to the left about a half inch and the thing fired up. It was off by just a little bit.

Also I had the Blue and Black wires mixed up. Black is for Accessories and Blue is Ignition Run.

Thanks for your help.

I went through a similar aftermarket switch wiring thing and sorted it out in my 73 Valiant. That was a few years ago though. I do recall the switch had additional unused wire. Connect it as received and blow the inst' lamp fuse. Good luck with it.

RedFish said:

I went through a similar aftermarket switch wiring thing and sorted it out in my 73 Valiant. That was a few years ago though. I do recall the switch had additional unused wire. Connect it as received and blow the inst' lamp fuse. Good luck with it.

Click to expand...

Yeah the old switch had a small blue/white ground wire and the new one has a small black wire. The connector under the dash has a spot for it but there's no wire in there. I don't think a ground is necessary anyway.