LT40 fuse keeps blowing

[jdtuttle]

I have a 1992 LT40HD. The 100amp fuse keeps blowing. I read a post awhile back about possible causes but can't find it. Any suggestions? Alternator? Wire frayed? Dead short?
Thanks,
jim

[Slabs]

A little further explanation of "keeps" blowing might help.  Is the blowing incident associated with anything you "do" or anything that just "happens"?  Just a couple of questions to help in your troubleshooting.  One thing you might do is when the fuse blows, connect a 12 volt bulb like a brake or turn signal lamp(a good 1 amp or better bulb) across the blown fuse.( the bulb should light if the short is still in evidence)  Then start disconnecting things in the buss that the fuse services.  Sometimes wiggling wires and connections may locate the short.  Someone should be watching the bulb constantly to determint the exact moment when the short is located. (bulb will go out)   An unusual short that I found once was the electric brake "breakaway" switch vibrated down and worked it's way through the hydraulic pump electrical cable and shorted it out and blew the big fuse.  I used an ohmmeter on that one but the bulb would have done well also.  A buzzer or other audible device could be subltituted for the bulb if don't have someone to help.

[MartyParsons]

The 12 V wire runs to the alternator, Starter and the battery terminal of the ignition switch. A light across the fuse with the fuse removed would work like Slabs mentioned. ( a 12 v test light works good) If it lights there is a short. ( without the ignition switch on)  These older Onan gas engine mills have issues with engine mounts, when the engine mount fails the main wiring harness rubbs above the up down motor. ( Some of these I have seen the tubing that holds the wires brittle from UV rays) There is a 1/4 bolt that sometimes rubbs there also. I am assuming the fuse blows with out the switch on. If it blows only when the switch is on then there is a short between up down switch, forward feed or another accessory powered by the ignition switch.
Do you have a operator manual for your mill ? The wiring diagram should be in the back.
Marty

[jdtuttle]

Thanks for the replys. It blows the fuse when I attempt to start. When I turn the ignition key on the motor will turn over once, then the fuse blows. It doesn't matter if it's been running for awhile or it's the first thing in the morning. The wire connection at the alternator is a little frayed. Could that be it?
Jim

[MartyParsons]

Unhook the small wire at the starter. If it does not blow the solenoid in the starter is shorted. If it still blows the small wire is shorted. I would use the test light accross the terminals with the wire disconected from the starter the test light will light up. ( save you $ on the fues. The test light will light to engerize the solenoid that is normal but it still could be a direct short.
M

[jdtuttle]

I think I found the problem. The alternator was replaced by the previous owner & the protective rubber on the electrical terminal wore through. It was just enough to contact the frame because the bolt stuck out a little to far. I replaced some old wires while I was at it. Seems fine now. I'm taking her up to Hannibal tomorrow for the maintenance program. Hope to learn a little more about alignment & maintenance.
Thanks for the help.
Jim

[Slabs]

Great.  It's a relief to know that it was something simple and cheap to correct.  In the mills with several  hours on them some electrical problems are likely.  Chafed wires, loose connections, dirty connections(to include crimped wire-ends) and improper hardware.  I often look for improper hardware that might have been substituted in a pinch.  One particular area is bolts, i.e. iron bolts substituted where there should be brass.  Yeah, brass is quite a bit more expensive but so are breakdowns.

Our mills vibrate a lot and are sometimes exposed to the elements out of necessity and as such suffer in the electrical systems.  As often as possible(between jobs) a good inspection of components would be benificial.

Hope this is helpful.

[squack]

we had a 1994 that the mouther board went bad on and did the same thing also I know of two 1992 mill's that had the same problum get intouch with mizer they can tell you how to troble shoot

[jdtuttle]

Went to Hannibal WM site today for a complete service on the mill. We had a 9:30 appointment & showed up at 8:00. I wasn't sure how long it would take to get there & I hate being late. Anyway they let us right in & started working on the mill with 3 guys. They had an emergency service call & two guys had to leave. Which was really benefecial to me. I was able to get my hands a little dirty & probably learned alot more about alignment & maintenance. Can't say enough good things about the service & dedication of these guys. Kyle & Scott have a great understanding & knowledge base & are only to happy to share. Mill is like new with lots of new parts. Can't wait to get into some logs.
Jim

[jdtuttle]

Still blowing fuses but I think I found the cause this time. The fuse service block assembly is plastic and it melted from excessive heat while starting the engine. I ordered a new fuse block upgrade. Hopefully this will solve the fuse problem.

[Slabs]

You're getting that troubleshooting down pat Bubba!!  Hang in there.