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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

420C-Electrical problems

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Joe in NH

08-13-2007 08:59:32




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I have a JD 420C which I've owned for many years without any major problems until now. It keeps on burning out the points and compacitors(I'm on my fourth set)I have changed the battery and coil. The problem is when I change the points it will start without a problem and run well but
if I shut it off and wait a few days it will not start unless I change the points or compactior or both. The points seem to be burned. Any suggestions. Joe in NH

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John-Paul

08-21-2007 11:34:42




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 Re: 420C-Electrical problems in reply to Joe in NH, 08-13-2007 08:59:32  
possum I agree completely. A cold engine needs a hotter spark to start easy. This method is old tried and true. And its completely possible its burning points and capacitor from too much power fed to the coil.

BTW, you can check to see if resistor IS or isnt working without any hassle. If you have a volt meter. Hook it up to the coil(leave other wiring in place). Now turn key to start. While starting the volts will be higher, once started it should drop volts (this is the power going INTO the coil not out to cap and rotor dont try to measure that part!).

Two things to also check. If rest doesnt help, check the coil it could be putting too much out do to failing. Also GAP THOSE POINTs. You prob did but its so important I wanted to mention it.

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Lavoy

08-13-2007 17:11:59




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 Re: 420C-Electrical problems in reply to Joe in NH, 08-13-2007 08:59:32  
420's did not come with a resistor from the factory, a 6 volt system does not need one. If it has one, someone has added it when they converted it to 12 volts. There is only one wire from the ignition switch to the coil on a 420, and it should not have a resistor. If your crawler has been converted to 12 volts, somewhere in there lies the problem.
Lavoy

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Joe in NH

08-15-2007 14:02:11




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 Re: 420C-Electrical problems in reply to Lavoy, 08-13-2007 17:11:59  
Thanks for the quick responce. The tractor still has the original 6 volt system. I can not find any modifications to the system. I have ordered a new ignition switch from JD. I have to start somewhere? Joe in NH



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original possum

08-13-2007 16:24:31




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 Re: 420C-Electrical problems in reply to Joe in NH, 08-13-2007 08:59:32  
The 420 should have two ways for the power to get from the switch to the coil. The resistor on the ignition circuit is bypassed when you hit the starter, sending a higher voltage. Once you let off, it sends it thru the resistor, either on the back of the switch or in the line. Some had an oil pressure switch that opened once pressure was made that will stop the direct link and put the resisted circuit in control. It may be the ignition switch or the pressure switch, but you are not getting the lower voltage while running. Probably not the resistor since they usually fail open if they fail.

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