CASE IH MX120 PTO fuse blowing.

[lightfixer]

Last year the PTO fuse blew a few times and a couple solenoids were replaced. Fuse continued to blow, uUsually after going over a little bump. We searched the wire harness and increased the fuse from a 7 all the way to a 30. Eventually it didn't take a bump to cause fuse to blow. Never saw a flash or smelled a burn and could not cause the fuse to blow at will. We found that if the hydraulic tank is completely full, the fuse won't blow. Looks like the time spent on the loom was a waste but have not identified the problem. Has anyone seen this before?

 

[RNeumann]

What you describe is typically a chaffing wire issue. Typically pulling, pushing, jerking and moving the wiring around will narrow down the location.

 

[LouNY]

I don't know on your MX120 but I do know that a heavy person in the seat of a Puma 125 with the seat most of the way back will pinch the wiring harness under the seat and cause all sorts of strange issues.

 

[lightfixer]

What you describe is typically a chaffing wire issue. Typically pulling, pushing, jerking and moving the wiring around will narrow down the location.

That is how we attacked the suspected short. Moved the harness, drove with the floor up and tried everything to reveal a short in the harness. No luck.

 

[lightfixer]

What you describe is typically a chaffing wire issue. Typically pulling, pushing, jerking and moving the wiring around will narrow down the location.

Finally some good news.
I went over to visit and got to spend time on this CASE tractor again. The owner was frustrated and not able to work the tractor like he should. He had been dealing with this blowing fuse issue for two years minimum.
A decision was made and a risk assessment was done. An 18 gauge solid wire was soldered in to an old 7.5 amp fuse and installed in the circuit. The tractor made a one minute route with PTO engaged and then stopped moving. The engine did run but the shuttle shift was unresponsive. The seat safety switch was tested and showed OPEN regardless of operator weight in the seat. This seat safety switch had passed a continuity test for OPEN/CLOSE every time it was tested over the last two years. Now it was broken and the intermittent fault was now permanent. NOW there was something to fix.
The seat safety switch was bypassed with a temporary jumper. The transmission engaged, the PTO functions correctly and the owner has shredded with a batwing for 8 hours across all types of terrain since then.
I have visited with several professional mechanics since this work was done. All were aghast that we were willing to bypass the fuse. None said they would replace a seat safety switch that passed testing.
Over the phone, Service Writers were never willing to say that their tech would fix a temporary condition and that they had not heard of this condition before. In a shop, I can only guess what the troubleshooting cost could have been without just a little luck.