I agree that it would work if you remove and rewire the plug so the wiring to the later switch is correct. But that is a change to the factory harness. Lol

No change to the actual wiring harness. Just remove the brass terminals from plastic and reinsert into replacement plastic holders.
No need to cut/crimp wiring.
Easy to understand: you're just replacing the earlier 2 plastics with the later 1 piece.
Doesn't require a degree in electrical engineering.
The earlier switch is larger cause it has a rheostat built into it.

As it's been said, just relocate the wires from the 2 plug connector to the one plug connector. Maybe this picture will help, sorry for the blurriness.

Thanks for the wiring diagram John. It's easy to see why the 2 plugs when put on the newer switch smokes since the F-1 and F-2 red & green don't align with the right terminal. You can use either switch and single or even the double plugs as long as you switch the wires to align with proper terminal.

A-brown (might have stripe) B-pink P-blue F-2 green F-1 red W- brown V10-18br

Thanks for the diaphragm, but if I am understanding this correctly, you will have to either put all these wires into individual plastic insulators or have a complete one from a 72 up wiring harness and just move all the wires? I think this would have been way over my customers head so I opted for the modified and rebuilt variable speed switch from Devinism for a little over $200 and it just plugged right into the customers new 70 harness..

Yes, you understand correctly. You made a good call going the K.I.S.S. method with consideration for your customer's skill level.

I think I will try to find either a 70-71 E or 67-69 A switch. I am not going to mess with the wires either.

???? It's as simple as removing a terminal front 1st plug & reinserting into the 2nd. Repeat until all are done.
Never understood how many are so hesitant to do even some simple wiring tasks on a 12volt system.
Now newer cars I can understand, but these older systems are simple in comparison.

Finding a used 72 up switch and plug in may prove just as challenging. Just call up Devinism and he can fix you up with a restored switch that will fit your 70 harness and plug.

Oh! I forgot my build sheet. This is what was under the front bench seat. Enjoy!

Lol! Wrong thread Robert