I have a very strange problem with the ignition switch on my 1971 1200. The engine will no longer turn off when I turn the key to the off position. I've checked the wiring under the dash and everything seems to OK. I've even replaced the alternator, still didn't help. No changes to the wiring was done to cause this happen. It went from working to not working.
What is strange about this is that if I pull the main connector off the dash pod, the ignition works and the alternator charges properly. If I reconnect the dash pod, the ignition switch no longer turns the engine off. However, if I ground the green wire to any other ground source (see the photo), then the ignition switch works. There are no breaks in any of the circuit traces on the dash pod. If I remove the charge lamp, then the ignition switch works. If I put the tranny in reverse, the switch also works. If I turn the signal light on with the ignition in the off position, the engine is killed. If I pull the windshield washer motor switch, this also kills the engine when the switch is in the off position.
Looking at the fuse box, there's a 10A fuse circuit labelled as "meter/reverse/regulator" on the fuse panel cover. When I pull the fuse, it kills the engine when the switch is in the off position.
The alternator has two ground wires attached to the Earth terminal. Both have good connectivity.
I unwrapped part of the wiring loom between the 4 blade ignition switch and the fuse box. Everything checks out, no broken wires or intermittent short when pulling or wiggling the wiring loom.
I pulled the ignition switch apart and cleaned the terminal contacts. They look good. The switch has a good positive feel in all of its positions. The blade connectors are all solid and making good contact between the switch and the connector.
After all of this troubleshooting, I'm wondering if its still possible that the ignition switch is the source of the problem.
Unfortunately, I don't have a spare switch to try. 4 blades switches are no longer available from RockAuto. They only have the 5 blade switches which is quite a bit bigger than the 4 blade switch.

Any suggestions as what to try next?

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I've had this kind of problem a couple of times and it was the ignition switch. I suggest getting a switch that is known to work and swapping that in.

It's also a common symptom of an IR (internally regulated) alternator mis-wiring. Try unplugging the alternator jumper wires and see i the problem only occurs when it is plugged in

However your dash wiring info make me think of a ground problem somewhere ... not sure what it could be

Quote:The green wire is for the CHG lamp. So it seems to be related to the charging circuit (alternator/regulator). It is normally 12V, but by connecting it to GROUND (earth) instead it wont feed 12V to the regulator (back through the CHG light). Normally it is no problem as the regulator has a diode and won't allow the alternator to be powered via this wire. When I first converted my 1200 to IR alternator the engine would not stop. All it took was the wiring connectors to the alternator, no changes to the car, to the meter, dash or wiring harness

Well, after a lot of troubleshooting on the wiring, I did not find any faults.
So, I looked at the ignition switch again. I discovered that the top plastic rotating plate on the switch mechanism was out of synch with the bottom copper plate. I accidentally stumbled across this when I turned it to the START position and it continued to click further clockwise instead of stopping. That was totally unexpected. I reinstalled the switch and sure enough, it worked. There must be a broken stop tab at the end of the START rotation. Anyway, I am not able to find a new 4-spade switch as they are no longer available. Instead, I found a 5-spade switch that will fit inside the key holder. All what is required is to make a short wiring harness between the new switch and the 4-terminal female connector at the end of the existing wiring harness and then route the new wires to the correct ignition terminals. The replacement 5 spade ignition is made by Standard Motor Products model US119.