John Deer 770 electrical start problems

[Donna1900]

We have a JD 770, The tractor was idling to warm it up, and died. Then when we tried to start, the headlights come on as well as the lights on the instrument panel come on, nothing else. We found the fuse we believe is associate with the safety switches to be blown and replaced it. With new fuse, we get the clunk for the fuel shut off solenoid, but when we try starting the fuse blows, again. It's been -16 if that makes any difference.

 

[bmaverick]

We have a JD 770, The tractor was idling to warm it up, and died. Then when we tried to start, the headlights come on as well as the lights on the instrument panel come on, nothing else. We found the fuse we believe is associate with the safety switches to be blown and replaced it. With new fuse, we get the clunk for the fuel shut off solenoid, but when we try starting the fuse blows, again. It's been -16 if that makes any difference.

On the old electrical with these Yanmar/Deere machines, it's good not to run them below the -10F unless the starter had been upgraded from the solenoid type to the OSGR type.

Some of the machines have Voltage Regulators (VR). I can't recall if the 70 series or the 90 series change away from that like the 50 series having them. If your machine has a VR, the windings in the solenoid-relay go bad too at negative temps. The upgrade is going to full solid state VR.

Another trouble with the 70 & 90 series are the engine kill switches going bad. These at times have been known to blow fuses. You would need a volt meter to check the continuity of the switch when activated and deactivated. And check the switch if the spring inside is too weak.

Lastly, the dreaded rodents. Since Fall till now, pesky rodents love to eat and gnaw on old electrical wires. There is something in the wire material they desire. This can cause bad shorts anywhere. The newer automotive GXL and Marine grade wires don't have this issue.

 

[Donna1900]

On the old electrical with these Yanmar/Deere machines, it's good not to run them below the -10F unless the starter had been upgraded from the solenoid type to the OSGR type.

Some of the machines have Voltage Regulators (VR). I can't recall if the 70 series or the 90 series change away from that like the 50 series having them. If your machine has a VR, the windings in the solenoid-relay go bad too at negative temps. The upgrade is going to full solid state VR.

Another trouble with the 70 & 90 series are the engine kill switches going bad. These at times have been known to blow fuses. You would need a volt meter to check the continuity of the switch when activated and deactivated. And check the switch if the spring inside is too weak.

Lastly, the dreaded rodents. Since Fall till now, pesky rodents love to eat and gnaw on old electrical wires. There is something in the wire material they desire. This can cause bad shorts anywhere. The newer automotive GXL and Marine grade wires don't have this issue.

Thank you for your insight. We will keep checking into these things. Our first thought was rodents, but have not found any chewed wires.

 

[bmaverick]

Thank you for your insight. We will keep checking into these things. Our first thought was rodents, but have not found any chewed wires.

I can give you 1st hand two examples of rodents.
- mice
- birds

 

[Donna1900]

I can give you 1st hand two examples of rodents.
- mice
- birds

Those pesky critters. We have found a temporary work around as current and impending snow conditions warrant immediate use of the tractor. As weather permits we will continue to look for the safety switches and test. So far we have not found and issues. Electrical issues are not easy. Thank you for your help. The starter is working well.