If it doesn’t crank with the resistor in place I’d say there’s probably a high resistance in the starter circuit causing excessive current draw and robbing the ignition circuit.
This is what you want...
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Pete, Thanks for re-posting this valuable information. If I'm not mistaken, this diagram and text was first submitted to this website by our own Bob Shellady, AKA supereal here. We haven't seen much of Bob lately, hope he's OK!
I had this info somewhere but can not find in my search. I looking to bypass the resister so the coil gets 6v only when starting. Any help.
Engine cranking speed or turn over speed has nothing to do with the ignition resistor. If it is cranking slowly that means there is lower voltage than normally required in your system. First load test your battery which means a heavy duty (300 plus amps) load tester to really load up the battery correctly. Not just the pissy 50 amp testers most auto shops use. If the battery passes its test you then start checking battery cables and terminal ends to make sure all connections are clean and tight. Old cable terminal ends develop bad connections where they are crimped or soldered onto the copper cable. Best to install NEW heavy cables especially if it is a 6 volt system. Of course the starter motor has to be in good working order and not worn out or half full of oil and crap. A good way to check for high resistance or bad connections at terminals is to touch them while the engine is cranking and if hot then something is wrong. Testing can be done with a voltmeter. Brendan is exactly correct in his statement about how the ignition resistor works. Most people dont know this. No good just guessing with electrics and swapping out parts in the hope of a fix. Testing and fault finding is the key. If you dont understand electrics then take your car to a good auto electrician if you can find one. Regards, Kevin.