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Discussion Starter #1
I'm no mechanic, but I have an old blade tractor (Massey 1805) that seems to have developed a dead short somewhere on a keyed power circuit.

What I've found so far:

First noticed big draw on dashboard amp meter when doing some blade work a week ago, everything normal until sometime that afternoon. Shut tractor down in the field.

Key in on position, big draw on the Dash Amp-meter, 3-5 seconds later the 25 amp breaker under the dash flips and breaks the circuit. Breaker resets, draw comes back on and trips breaker again, maybe a 5-10 second cycle.

No draw when key is in off position.

I jumped the starter to bring it over to the shop, starts and runs without issue, not drawing battery down when key is off.

I unplugged the wiring harness from the engine to cab, and that eliminated the draw, cab fan, radio, ect still turned on/ran so would i be right to think its somewhere on those circuits.

I think I'm looking for a big bare wire on a keyed power circuit, maybe an internal short in the starter solenoid? All of the wiring on this old tractor is a mess, it's kind of a wonder it hasn't burned down already. Something that can take more than 25 amps without getting hot is not some small wire shorting out somewhere, is this fair to assume?
 

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well instead of unplugging the harness, disconnect the breaker that keeps tripping and find out what it controls, problem solved, you now know which wiring to go after. The wiring is a mess you say, so that means someone has ****** with it, so without actually tracing stuff back there is no way to say at all where the problem is. Not that hard on a tractor, only a few circuits to start with.
 

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A short that bad you should be able to follow the circuit and check for something that is hot
 

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I would look at the live wire from alternator. Maybe it has rubbed through and shorting on the engine block?
 

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I unplugged the wiring harness from the engine to cab, and that eliminated the draw, cab fan, radio, ect still turned on/ran so would i be right to think its somewhere on those circuits.
If I am following you correctly, you unplugged the harness coming out of the cab to the engine, and the circuit breaker quit blowing, and the cab functions still worked? That would narrow it down to wiring to the alternator ( or as suggested, alternator itself), or wiring to the sensors, oil pressure and temperature, and the Murphy sensors. I don't think there is anything else on that tractor that would have live keyed power ahead of the cab is there?

Disconnect the alternator first.

Check for any farmer added wiring, such as relays for extra lights etc. with poorly protected or routed wires.

Starter can't cause a draw through the ignition with key on. Unless the ignition has stuck in start position, starter should be getting really hot if that were the case.
 

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Discussion Starter #8
Ended up being a short in the fuel shutoff solenoid, spent about 15 minutes with a knowledgeable neighbour last night tracing it.
 
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