"Key Stop" Fuse Burning Out

Minerboyd

New member

Equipment
B7800
May 6, 2013
6
0
0
Apple Valley, Utah
I have a 2007, B7800-HSD (W/Mid PTO). For some reason the 5 amp fuse located at the top of the fuse box and labeled "Key Stop" keeps blowing for what appears to be very random events. At first we noticed it would blow when we would Raise/Lower or Tilt the front bucket, then it started happening when we would apply the "Forward/Reverse" pedal. After I install a new fuse I can normally run the tractor for only a few minutes before the fuse will blow again, (less than five-ten minutes of run time before the fuse will blow and usually when pressing on the forward/reverse pedal). I thought it might be a faulty "Safety Switch" from the PSD system so I bypassed the switch that is controlled by the forward/reverse pedal, I connected a wire between the connector that would normally plug into this switch hoping that if the switch was faulty then it might prevent it from shorting out and blowing the fuse, (unfortunately this made no difference).
I am hoping that someone can help me figure out where I should start testing to find out what might be causing a short in my electrical system that would cause this specific fuse to blow when the forward/revers pedal is applied. I have tested and made sure I have a good battery ground and that the positive cable from the battery is fully connected. I don't know if I should start testing for anything specific such as a relay or other PSD switches, I am not sure which wires I should try to test or what I should test them for. I noticed that when I tested the wires that connect between the safety switches I got about .118 ohms resistance on the 2000 scale, these wires did have two small items connected to the wires between the connectors, I was testing and when I unplugged and tested these items I got full resistance when I tested them one way and then after reversing the test lead polarity to test the same plugs the other way, I got between .110 and .118 ohms resistance.( I assume this is why I had between .110 and .118 ohms resistance when I tested the wires because these items were connected in the line between the two connector points I was testing). Since these items only allow the power to go through the wires in one direction and with some resistance, I assume they are working correctly whatever they are. (if anyone can tell me what these tiny items are and if my assumption is correct I would appreciate it).
I tested the safety switch for the MID PTO using an OHM meter and it is open when the Mid PTO is Not Engaged and Closed (full resistance) when the PTO is engaged, (I assume this is correct since it is the same results I got when I tested the safety switch for the forward/reverse pedal). Even though the F/R pedal switch appeared to be working, I disconnected the switch and bypassed it because the fuse appeared to blow when that pedal applied an I was hoping that disconnecting it might help (it made no difference and the fuse still blows).
I am now hoping someone can tell me if I should start looking for a bad relay or switch or if I should focus more on finding a broken or partially broken wire that may be causing the fuse to blow. If I should start testing for a faulty Relay, how do I test them, and where are they located, the only relay I could find was one located in the front panel on the left side near the tachometer connection cable.
Thank you in advance to anyone that can give me specific wires or items to test along with instructions of how to test them or what I should be looking for to locate this elusive and random cause of the Key Stop fuse being blown every five minutes.
 

Jim L.

Active member
Jun 18, 2014
811
86
28
Texas
Sounds like a short. Probably rubbed insulation or the like.

It would help for you to show your diagram for your particular model.

Then we can tell you what to unplug to fault isolate.