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1930 Plymouth Generator Cutout switch always on

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   I have a 1930 Plymouth 30-U that's been having electrical issues.  It's had trouble starting and then draining the battery. 


   So far, I have a battery that's about 3 months old and has been draining, even after I drive it, to the point where the car won't start. The same thing happened with the old battery, which was about 3 years old.  Next, I had my starter tested, as it would fire up about 1 out of every 12 times I pushed the starter pedal.  It tested fine but needed to be thoroughly cleaned, so that took care of my starting issue.  I then recharged my weak battery this morning.  The car fired right up within a nanosecond.  Great! 


    Now concerning the potential battery issues, checking the Amp gauge, the amps were about 3 at idle, then would go right up to about 22 when I revved the engine.  I made some adjustments to the generator and now it idles at about 1 amp, and will not go above 12 when I rev the engine, which is what the manual recommends.  The one thing I've noticed is that my cut out switch on top of the generator always seems to be on, no matter what the engine speed.  The generator has been professionally rebuilt about 2 years ago.  According to the owner's manual, it should be off at idle and only switch on at a certain engine and/or road speed to charge the battery.  What could be causing this?  I would think if the cut out switch was broken, it would just always be off.  I'm guessing that since this is always on, and I was running at a high rate of charge, that I may have fried my previous battery or done other damage to it.  Any suggestions on why my cut out switch is always on?  Thanks!!!  -Chris

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You should think of the cut-out on top of the generator as a one-way valve. It allows the generator to charge the battery, but it will not allow battery current to flow to the generator when the engine is off. It isn't a regulator and doesn't open and close while the engine is running. It's only designed to cut the circuit between the battery and generator when the engine isn't running. If it's not working properly or stuck, the battery will drive the generator like an electric motor and kill the battery in pretty short order. With the engine off, listen carefully to the generator to see if it's humming or feel it to see if it's getting warm. If it uses a drive belt, remove the belt and see if the generator is being turned by the battery. All easy tests that will confirm whether it's the cut-out. If not, you have a drain elsewhere in the system and should start testing each circuit to find it.


If it's a point-style cut-out, you can try cleaning and adjusting the points to make sure they are breaking contact when the generator is not turning. If not, it may need to be replaced. There are modern diodes that you can retrofit inside the original case to look authentic or you may be able to find an NOS or rebuilt unit. 


My wife's '56 Chrysler came to us with a 100% dead battery and it was obviously brand new--the previous owner threw it in there as it was going on the trailer to come to us. The minute we put a charger on it, the generator started to hum quietly and I could feel it with my hand on it. A new voltage regulator (which has the cut-out built in) cured the problem. 


Hope this helps!

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Cutout goes to “ON” and stays that way as long as the generator voltage is greater than the battery voltage.  If the car is running and the generator is working correctly the battery will charge at the level determined by the third brush adjustment.  

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   Thank you, that was very helpful.  I think this clears everything up for me.  The generator does not run when the car is turned off.  I pulled the cover on the cut out switch and the points are not touching when the ignition is off.  Also, I always disconnect the battery when I park the car.  Too many stories about fires, so that couldn't have been the long term issue.


    Wasn't sure about the cut out switch always being on when the car was running, but since that appears to be normal, I think everything is back to working correctly.  I think my issues were a weak battery combined with a very dirty starter.  Once I took care of both of those problems and adjusted the third brush to put out less power from the generator (only up to 12 amps), I think I'm good to go.  Time to put on the side curtains and do some cold weather driving.




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Its OK for the cut out to make the points connect (i.e. ON) at idle. At 1 amp positive on the gauge you're probably at the threshold of where the generator is spinning fast enough to engage the cutout, which is fine. Its when the engine is off where it needs to open and disconnect itself from the battery.  A test you should consider is putting a Volt Ohm Amp Meter in line with the battery lead and see if there is any current while the ignition is off and all accessories are off, doors, closed, etc. Verify the test set up is right by turning on a light or opening a door to get the courtesy light to illuminate. A battery should not drain on its own. Its possible the coil of the cut out is malfunctioning and draining the battery. There is a spring adjustment on the cutout that will force the cutout to open at low speeds. Usually means bending a copper tab with needle nose pliers. Make adjustments with the engine off and battery disconnected to avoid creating another problem.

Edited by Friartuck (see edit history)
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