Ready to tear my hair out. Our service truck has an Ingersoll compressor with a 3 cylinder deere engine. Its a 3179 with the rotary pump I think called roosamaster. Theres a single wire to the pump...12V to start and cut ignition to shut off. Well the other day we couldn't shut it off with the switch...so replaced the switch...same issue. So then replaced the relay (not the big relay to the starter but the small relay next to the switch which I believe powers the safety switches?)....and the new relay did not fix it. If the battery is connected to this compressor there is 12V at the fuel solenoid on the pump. Can anyone even guess what switch or sensor or something is stuck ON? Thanks -signed soon to be bald
I've seen an alternator cause that issue
Thats the only thing I didnt disconnect...I tried to but it felt like I was going to snap the stud on the back of the case holding the positive wire. Since its all thats left I am going to have to go for it tomorrow. I think its only 2 wires back there one is spade connection and other is the 12V to stud.
On stuff like that I often disconnect the + battery cable. Then connect a fused jumper wire to the affliction, fuel pump wire in your case. Then search for what it is feeding with a test light. Maybe a relay, or harness problem? Pull fuses and relays one at a time. When does the light go out?
Is there a legible wiring schematic on the machine somewhere ? Is there is a bypass switch on the panel that could be stuck closed ? If there is a bypass switch then often there is also a diode in the circuit that if shorted could cause the injection pump to stay powered. If there is a diode I would think it would be in the signal wire to the alternator.
What is the model and serial number of your compressor?
And the engine serial number?
Just a wild guess, but it sounds like a welded relay contact. Start pulling relays until it quits. Once you pull all of the relays and if that doesn't fix it, call ghost busters......or has someone put a jumper wire in recently and forgot to tell anyone?