# John Deere 318 electrical problem. Dies when I engage transmission



## GooseRancher (May 3, 2014)

I've been burning up weekends trying to solve this problem, and I'm about to give up and take it to a shop. But, I thought I would ask here, first, though, and see if you tractor veterans could save me some money.

I inherited a John Deere 318 that seemed to be working fine. I had to replace a battery cable because the terminal clamp was broken. Everything seemed good, and it started up and ran after the replacement fine. I engaged the front PTO without a problem and the transmission engaged just fine because I drove it around for a minute. Then I saw smoke that smelled like burning plastic.

I disengaged the battery cables, and looked for the problem. The end of the battery cable that I bought had a lot of exposed metal at the starter terminal end, and because the starter terminal is in such a tight space, the cable end with bare metal rotated into contact with the chassis when I tightened down the nut and created a short. 

I next found that the two wire connector to the front PTO was melted and burned. Since that was the only obvious issue that I saw, I replaced that connector and started the tractor back up. I started fine, but when I engaged the front PTO, the 20 amp fuse burned out immediately. I thought, fine, don't need the front PTO right now (just the back), so I disconnected the front PTO clutch completely. 

The tractor again started up fine after that. But, the engine died immediately when I tried to engage the transmission. The tractor was fully warmed up and running like a champ. So, I got back under the hood and looked for the next issue. I found that the 3 wire connector to the voltage regulator was melted through between two of the wire ends. So I replaced that connector. That didn’t fix the problem.

I printed off a bunch of wiring diagrams and started to try to troubleshoot the electrical system wire by wire, connection by connection. I couldn't see any more problems. It seems like the tractor is shutting off due to a malfunctioning safety switch. The former owner had by-passed the seat safety switch by just twisting and black taping the two leads going to the seat together. I replaced the tape with a wire nut to make sure the connection was good, but I couldn’t re-attach the safety switch. That did not fix the issue. 

Chasing the problem around the electrical system, I found something else that I *think* might be the problem. My multimeter was showing that the oil pressure switch is closed when the engine is off. Is it supposed to be? It looks like the oil-pressure sensor is tied into the safety switch system that will shut the tractor down when either of the PTOs or the transmission is engaged. The oil pressure light stays on after the engine is started and running fine. Looking at the wiring diagram, there is a direct circuit from the PTO/Transmission switches through the oil pressure sensor. Could something have been messed up on that line when I created the short with the battery cable?

I've been wrestling with this issue for some weeks now, and I really need the tractor and back pto going so I can mow my yard and till my garden. Any help would be really appreciated!

Thanks!


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