Kubota :L2900GST Blowing Main Fuse

[PitbullMidwest]

It's finally warmed up enough to look at an electrical problem that cropped up during the snow storm last month. I have a 1998 Kubota L2900GST and after plowing the road a couple of times I went out for another round, turned the key, glow plug preheat came on and then I heard a "click" and lost all electrical power. After a little checking I discovered that the 40 amp main fuse was blown. I replaced the fuse and turned the key and immediately blew the fuse again.

Fast forward to today. I traced all the wires in the starting circuits that might be causing a dead short and didn't find any. After consulting my service manual I pulled the starter relay and tested it as instructed and found that it was bad (no conductivity). While I was at it, I also checked the glow relay which passed but was unable to check the glow controller as it required power at the key switch to test.

Since it's too late to get a new relay today, I thought I'd ask the brain trust for some more knowledgeable advise. Is it possible that the bad relay is what is causing the fuse to blow OR is the fuse designed to blow to protect the relays and have a dead short somewhere else. At $5 a fuse I'm not a fan of trial and error. Any help would be greatly appreciated.

 

[ThomasH]

A bad relay can cause two things - either nothing on the circuit that it feed will work, or it stays on all the time. If the relay is for the glow plugs and it sticks on, the glow plugs would continue to be lit. That would take some time before blowing a fuse, at least 20 or 30 seconds. If the relay is not functioning, nothing will happen.

Either way, it doesn't sound like a glow plug relay problem as it happens quickly. Possibly a bad glow plug or wiring short to the motor block or something like that would be my guess.

 

[skyhook]

Does the fuse still blow with the relay "removed".
If it does, it could be your ignition switch, also make sure all the wiring around the starter is good.
The fuse is there to protect "anything" in that circuit, ignition, relay and whatever the relay controls.
Process of elimination is how you'll find your short, (have a few good fuses on hand).
You can also (with the key OFF) use a continuity meter ( the kind that beeps when you have continuity)
one end is grounded and the other you use to probe a power wire (B+) if you have continuity on the wire, you have found your short, (probably).
Think of the conditions on that day and what the tractor was doing, this may help you in your search.

 

[PitbullMidwest]

Skyhook, I haven't had a chance to test it with the start relay removed, I'll pick up a couple of fuses and give that a try. In the mean time, I spoke to the dealership and they said they've seen a bad start relay blow the fuse but the only way of knowing if that's the cause is to replace the relay and see if the fuse still blows.

They have to order the relay so it looks like it will be next weekend before I'll know.

 

[PitbullMidwest]

Well the verdict is in, I took all of the relays and key switch to my dealer and had them tested. Bad start relay and bad key switch, they said I most likely had a dead short and that is what was blowing the fuse and might be what caused the relay and key switch to fail. After installing the relay and switch the fuse blew as soon as the key was turned. At $5 a fuse, I opted to replace the fuse holder with a auto reset circuit breaker and my BIL and I started tracing wires, he eventually found a mouse chewed wire between the key switch and glow relay. We replaced the wire, reassembled the dash and I'm up and running again. :thumbsup: