When I crank the engine after it is at normal operating temperature it won't start unless I back off the switch just enough to stop cranking and it starts immediately. It seems there is no power to the ignition while cranking but has power in the run position. Does this mean the switch is bad or is something else going on?

Also, in searching for a switch, I am finding switches with numbers 685, 672 and 674. Mine is 686. They all look the same to me. Will these other numbers work or do I have to find a 686?

Thanks for any and all help.

 

I believe that's the cut of the keys in the difference in numbers

 

Does that mean any of these switches will work? And do I have a bad one?

 

It means unless you put a test light at various places in the engine ignition circuit and do some checking, you are merely guessing at the problem and so is everyone else.

 

Problem could be with the switch, but it could also be a problem with the starter solenoid and/or the pink wire from it back to the coil. As Mike says, you need a test light or multimeter to find the right answer.

The 686 switch is a 1967 ignition switch. It will work okay. For 1967 model year the key blanks were different than for 1966, but the housing should be compatible. Not certain of the correct switch number for 1966 model, but a Google search should find it.........or perhaps someone with an original 1966 car can provide.

I will get the number and post it later if no one else replies today. Since it is a 1966 car, the switch number will be lower than the 686 for 1967 model year..........it won't be higher.

Larry

EDIT: Appears the correct number for 1966 is #673 (#1116673) They are a bit rare and price is $$$$. Make sure you need it before buying. There are other USA made switches available without the GM part number/logo that cost less. A "good buy" for a NOS original is probably around $100-125...........but those currently advertised are much higher than this. Make sure you need it, and if originality is not paramount, check for Standard Motor Products or something similar. A GM NOS 686 cost is probably on par with the 673. What key blank are your current/existing keys??

 

9448. They appear to be original.

 

If it doesn't have an A or B or C or D letter on it and the blank says B&S, it is probably an original key blank. The four digits you posted are likely your key code for cutting new keys.

The #673 or #686 or Standard Motors Product equivalents should all work for you. You just reuse your lock cylinder and key.

Larry

 

It most likely means that the pink wire circuit from the outboard small "R" terminal on the starter solenoid that supplies 12V to the coil only when the starter is cranking is open/disconnected or damaged. That pink wire from the "R" terminal is the ONLY source of power to the coil with the key in the "start" position.

 

Can the ignition switch be rebuilt or taken apart to clean the contacts?
Is replacement the only option?

 

Yes, it can be disassembled and cleaned, but I've never had one apart myself; the guys who have say to be very careful when you separate it, as there are little springs in there that want to fly everywhere.

 

If I were a betting man, I'd bet a lot that the switch is not your problem. It's putting 12v to the starter solenoid in "start" and 12v to the ballast resistor in "on". That's its job. The 12v to the coil during "start" comes from the solenoid. Read JohnZ's post #8 above again.