91 - 520H - 30A fuse holder fried to a crisp

[soofoodude 6]

Good Evening folks - About 10 years ago the power from the battery fried the engine connector so I bypassed it with a new line directly to the fuse box.  The end of last year and this spring the battery wouldn't hold a charge.  While putting in a new battery I figured I should check the fuses.  The 30 A fuse was soooo fried I had to get a pair of vice grips to get what remained out of the holder.  The last time I used it I put in a new fuse and she started right up - and then I took the  fuse out and mowed the raging blue grass that seems to be growing an inch per day.  Needless to say I lost charging ability and the new battery is about dead.  I am assuming there is a some kind of short somewhere down stream of the fuse - but it must not be a dead short or it should trip the fuse right away?.  According to the wiring diagram it appears there is a white wire heading to the tach regulator (the tach quit two years ago) and a purple that heads to the Start relay and on to the starter and other destinations.   Would anybody have a guess as to the likely culprit? - The tach side or the starter side?   I also had a different relay problem 6 or 8 years ago but can't remember exactly what the malfunction was.   If anybody has a guestimate, it would be appreciated.

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[squonk 42,579]

I'm going to guess the starter side. Enough current, probably 25A or so was flowing for quite a while to melt it and not make it pop. A bad connection in the fuse box (they are known for that) causes resistance and heat. I would replace the box with individual fuses and then search for a current drain with the key off.  If none are found I would guess the cause was the FB connection. I've seen this in automobiles countless times especially on high amp circuits like blower motors and AC compressors.

[ericj 1,578]

if the voltage regulator doesn't see 12 v it can short out. once i started my 520 and loaded it on the trailer for the big show. once at the show the tractor would't start, found blown fuse, as soon as i replaced it and turned the switch on it would blow again. found regulator dead shorted to ground. thought was the fuse had blown earlier ad running it with out the fuse blew the regulator.

 

 

 

 

eric j   

[squonk 42,579]

You know what they say, "Let an Electrician Check your Shorts! 

[soofoodude 6]

Thanks for the info fellas.  Since my original post - my 520 may have went kaput.  Was mowing along and she all of a sudden lost power, began missing like it was running on half of one cylinder and proceeded to quit.  Going to send her to my brother who is a real mechanic for a post mortem.  I hope I didn't lose the rear cylinder - it has about 650 hours on it.  I will update when I see where I am at.  Thanks  again - for your dedication to the WH world, it is greatly appreciated.

[soofoodude 6]

Update.  We traced the prior problem to the voltage regulator circuit.  we replaced the V.R. and fuse holder.  We also bi-passed the main harness connector as my mechanic(brother) had seen a lot of problems with those type of pin connectors and higher amperages.   We changed the fluids and filters but now I have a flashing oil light - go figure.  But at least my tach  is now running.

[lynnmor 7,575]

A flashing oil light ain't good, don't continue to run it with low oil pressure.  Check the compression to see if that shows a problem.  You might be looking at a major tear down.

Edited July 9, 2016 by lynnmor

[soofoodude 6]

We did a compression check before we worked on the wiring and changed fluids. Both cylinders showed 120 something.  Searching a bunch of other threads, it looks like the sensor / sending unit may be something to look at.  I will have to get a gauge and check the oil pressure before I put her back to work.