Topic: 35 engine run on


franklin    -- 09-06-2024 @ 7:04 PM
  We are getting my beloved 35 back on the road. The engine is running but when I turn the switch off, the engine keeps running. We bypassed the switch and the engine keeps running. We replaced the resistance unit, no change. Could the problem be the coil or the condenser? Has anyone else had a problem like this? Dave


carcrazy    -- 09-06-2024 @ 8:17 PM
  Have you replaced the generator with an alternator?
If you have, the engine may continue running after you turn off the original ignition switch.

This occurs because the alternator has an output at idle and low RPM whereas the generator does not. This current output from the alternator travels backward through the ignition switch to the ignition coil allowing the engine to continue running.

If you don't want to install a modern type of ignition switch with an "accessory post" which isolates the alternator output from the ignition circuit, you can install a "DA Plug" on the alternator to prevent the current back flow to the ignition system.

The DA Plug is a diode that is mounted to the alternator. It is available from several vendors. One of these vendors is Fifth Avenue Antique Auto Parts, www.fifthaveinternetgarage.com

Hope this solves your problem


Drbrown    -- 09-07-2024 @ 8:07 AM
  Generator or Alternator, you obviously have a bypass condition in your electrical system that is feeding the Ignition Coil. Your post indicates the engine runs okay; just won't shut off. A faulty coil, distributor or condenser would present an engine starting or running deficiency.

I can't comment much if you are using a generator as it uses either an exterior control box or cut-out pending vehicle year. One really needs to be in-person to examine the system. To start, I'd check the input terminal on the Ignition Coil to see if it's alway "hot" (key on, key off or key switch disconnected). Is something else feeding the coil ? I assume with your complaint that terminal will be "hot". Then start tracing the wiring from there backwards toward the Switch and beyond to look for a constant connection to the battery. Although you replaced the resistance coil on the Ignition System did you disconnect the switch entirely to see if that "broke" the feed to the coil ? "Jumping" the switch only ensures that electricity gets to the coil.

My '47 uses an Alternator and has not presented a back-feed problem. The charging wire from the Alternator first runs thru the Dashboard AMP Gauge, then thru a Voltage Meter I installed, then to a terminal connection point that connects the charging current to the battery and the overall electrical system. To start/run the engine, the electricity there then goes thru a fuse to the ignition switch. So the feed to the Ignition Switch is always "hot" and the key must be turned on to energise the Ignition Coil.

Related to Alternators, I had problems purchasing an Alternator that functioned correctly ..... typically off the shelf, their built-in diodes allowed excessive voltages that burned-out my electronic ignition modules. My local electric repair shop kept testing my purchases until we found one that worked correctly.

This message was edited by Drbrown on 9-7-24 @ 9:32 AM


40 Coupe    -- 09-08-2024 @ 6:55 AM
  The ignition switch opens the ignition circuit so the car can turn off. If there is a broken part or a conductive part in the switch the engine can continue to run. Take the switch apart with the two screws in the rear. If the engine is experiencing Run on which is rare for the early ford make sure the carburetor idle plates are closed to their stop screw. What engine do you have and what carburetor?? Remove any jumper of the ignition resistor or the ignition switch. If your removing the ignition switch jumper to stop the car, the ignition switch may have closed contacts which also have to be opened by placing the switch in the off position. The resistor is there to lower voltage to the coil, high coil voltage will cause the coil to be destroyed over time. Placing a jumper on the ignition switch and failing to remove it when the car stalls will cause the ignition coil to burn out. The same will happen if the ignition switch is left on and the car is not running.

This message was edited by 40 Coupe on 9-8-24 @ 7:06 AM


franklin    -- 09-08-2024 @ 7:42 PM
  My grandson and I discovered the problem. It was the cutout on top of the generator. My 35 is completely stock. We had 3 more cutouts in the V8 parts drawer so we put another one on. Bingo, car shuts of with the ignition switch. Dave


40 Coupe    -- 09-09-2024 @ 4:48 AM
  So your car was not running nor experiencing run-on but being turned over by the generator. Good you found the source of the problem.


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