Voltage Regulator on 12v diesel system

Paperhorse · Feb 6, 2016

[b:3f40d82053]Problem[/b:3f40d82053]: Tractor will not crank when volt meter is installed. Voltage at the solenoid is 8v. When taken out voltage goes to 12v and tractor will crank.
[b:3f40d82053]Installation[/b:3f40d82053]: Restoring a 1952 MF 135 w perkins 3 cyl diesel.
Bought all new, voltage regulator, volt meter, rewired completely using "Yesterday's" tractor shop manual. Swapped out 2nd volt meter with no difference. Volt meter is in the battery to regulator wiring per diagram.
[b:3f40d82053]Question[/b:3f40d82053]: Do I have a faulty regulator even though it is new?

Steve@Advance · Feb 6, 2016

Volt meter or amp meter? They wire different. It would have originally had an amp meter.

With an amp meter, the power flows THROUGH the amp meter. Power from the battery into one terminal, through
the meter, out the other terminal to the rest of the electrical system.

http://ww2.justanswer.com/uploads/indytech/2012-03-25_215414_ammeterwiring.jpg

With a volt meter, power is supplied TO the volt meter from the switched side of the ignition switch. It
simply reads the voltage present and is not a part of the circuit.

http://www.holden.co.uk/productimagesWD/070_313.jpg

Deere Mark · Feb 6, 2016

Voltmeter??? Are you sure you don't mean Ammeter? Tractors almost never have Voltmeters. An Ammeter is a very low resistance device. A Voltmeter is a very high resistance device. You can not substitute a Voltmeter for an Ammeter. As long as the battery Voltage is OK, the engine should be able to crank even if the regulator is faulty (and with the Ammeter connected or not connected according to the wiring diagram I found on the web). (unless the regulator is really bad and is shorting something to ground).
MF 135 was built from 1964 until 1975.
MF 35 was built from 1958 until 1965.
So if you have a 1952 MF 135, it might be really rare. Maybe it is 1972.

mgriff543 · Feb 7, 2016

I don't believe your battery is any good. Not even the starter load should drop a fully charged good 12v battery to 8v. No gauge I have ever seen could provide that amount of resistance. Sorry i can't be more help. Mike

Paperhorse · Feb 7, 2016

Super thanks for replys. New to this but love Yesterdaystractors. Staff are very helpful and shipping has been super fast. The original meter was too rusted to see just what it was. Bought what I thought was correct. I know nuts and bolts but not much electrical.

JimS · Feb 8, 2016

Check your grounds. Simple and no expense cures first.

Ensure that your ammeter is properly grounded. To further test a ground issue, run a ground wire from the ammeter ground to the
solenoid ground and check your voltage again.

I had an issue with a vehicle that ate voltage regulators. I ended up running a permanent ground wire between the regulator
ground and the alternator ground so that they were sharing the same ground. I have not had a problem for years.

Voltage Regulator on 12v diesel system

Paperhorse

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Steve@Advance

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Deere Mark

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mgriff543

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Paperhorse

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JimS

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