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Blowing Main Fuse?


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#1 artbuc OFFLINE  

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Posted August 06, 2015 - 06:23 PM

Just started blowing the main fuse between ammeter and starter solenoid. First blew while mowing grass but it also blows when running tractor without mower (PTO) engaged. Does not blow with engine running and tractor not moving. New fuses last a minute or less. Looked at manual and was surprised to see it called for a 30A fuse. I have been using 20A for as long as I can remember and never had any blow. Easy to understand fuse blowing during crank but while running? While running, there is almost no current running through that fuse. I was never watching the ammeter when the fuse blew so I do not know if there was a current spike. Ammeter seems to be working ok. It will briefly deflect while cranking and quickly move back to zero as it recharges the battery. I could put in a 30A fuse but that does not explain why a 20A has been working fine for over 20 years. Any ideas? Thanks.


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#2 shorty ONLINE  

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Posted August 06, 2015 - 06:31 PM

Did you check for any wires that could have been rubbed bare and shorting out?


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#3 artbuc OFFLINE  

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Posted August 06, 2015 - 07:09 PM

Did you check for any wires that could have been rubbed bare and shorting out?

Just quickly...will have to look more closely tomorrow. I could see the wires around the ammeter and solenoid...they look ok. From my crude understanding of the electrical system, I can not understand how bare wires anywhere else would cause this problem. The way fuses are burning out, it seems much more like a steady draw of excessive current rather than a spike from a bare wire bumping against ground. Re fuse size, the Kohler M18/20S service manual shows a 15 amp and 25 amp set-up. I am pretty sure my M18S has the 15A whereas the M20S has the 25A system. This explains why my fuse is 20A.


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#4 DougT ONLINE  

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Posted August 06, 2015 - 07:38 PM

I would have to see a wiring diagram but usually all the current flowing in the system goes through that fuse. If it blows with the pto off, it would have to be before that. Does it blow with the key off? Does it blow w/key on engine not running? It could be a shorted out switch, ammeter, regulator, ect. Start disconnecting stuff and see when it quits. You might want to wire something like a self resetting circuit breaker in there to use for testing. A test light in place of the fuse would tell if you found it too. Just jump the light across the fuse and if there is a ground in the circuit it would light. You need a wiring diagram for whatever you are working on to help with diagnosis.


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#5 artbuc OFFLINE  

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Posted August 07, 2015 - 03:10 AM

Did you check for any wires that could have been rubbed bare and shorting out?


Think I found it. A portion of the harness was hanging down rubbing against the drive shaft. Must have happened when I replaced the fuel pump and throttle cable last week. Will repair wire and report back results. Thanks.
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#6 artbuc OFFLINE  

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Posted August 07, 2015 - 03:11 AM

I would have to see a wiring diagram but usually all the current flowing in the system goes through that fuse. If it blows with the pto off, it would have to be before that. Does it blow with the key off? Does it blow w/key on engine not running? It could be a shorted out switch, ammeter, regulator, ect. Start disconnecting stuff and see when it quits. You might want to wire something like a self resetting circuit breaker in there to use for testing. A test light in place of the fuse would tell if you found it too. Just jump the light across the fuse and if there is a ground in the circuit it would light. You need a wiring diagram for whatever you are working on to help with diagnosis.


Some very good tips. Thanks. Yes, the service manual has excellent circuit diagrams which are invaluable for troubleshooting.
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#7 artbuc OFFLINE  

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Posted August 07, 2015 - 04:05 PM

Think I found it. A portion of the harness was hanging down rubbing against the drive shaft. Must have happened when I replaced the fuel pump and throttle cable last week. Will repair wire and report back results. Thanks.

The damaged wires supplied power to the headlights and front PTO, downstream from the switches. The PTO wire was badly damaged and caused the short. I must have been mistaken when I said the fuse blew while operating the tractor with the mower engaged or disengaged. I rerouted the wires so they can no longer snuggle up with the drive shaft. 






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