Bobcat 753 Glow Plug operation

carlbman · Dec 3, 2014

Good morning,

I am a newbie to the forum and hope I have this posted in the correct forum.
I recently purchased my first Bobcat. It is a 1993 Bobcat 753 with 2300 hours. It is in realitively good shape. I found that the glow plug relay and socket that is located above the battery had shorted and both had to be replaced. Since the relay and socket had fused together, I am concerned about the operation of the glow plug solenoid.

When the ignition switch is turned, on the glow plugs relay energizes. I have not tried to leave it on for an extended period of time for fear of burning the glow plugs out. Some glow plugs are controlled by a push button, yet some are controlled by the ignition switch. I doubt that these are controlled automatically. I have reviewed the wiring schematic and the control lead of the solenoid goes to the "System Control Unit".

My question, how are the glow plugs controlled (ie, is it automatic or by a switch)?

Thanks for any help!

SSdoxie · Dec 4, 2014

That age 753 the glow plug worked with key turned left and hold to pre-heat then would also engage relay when key in Start Position. I suspect someone hooked the glow plug wire at the ignition switch to the "run" terminal of the switch. Fairly sure they did not have auto-timed glow plugs on that model in '93, might have them if it is BOSS display unit bit I'm not sure. Bobcat did come with timed glow plugs/preheat at start of the G-series (2000) production year.

Danny C · Dec 5, 2014

Dennis is correct with turing and holding the ignition switch to the left. There was no auto-timed, you had to hold for 10 seconds, 20 seconds, 30 seconds, etc. depending on temperature. I'd say Dennis' guess of incorrect wiring is likely accurate.

SSdoxie said:
That age 753 the glow plug worked with key turned left and hold to pre-heat then would also engage relay when key in Start Position. I suspect someone hooked the glow plug wire at the ignition switch to the "run" terminal of the switch. Fairly sure they did not have auto-timed glow plugs on that model in '93, might have them if it is BOSS display unit bit I'm not sure. Bobcat did come with timed glow plugs/preheat at start of the G-series (2000) production year.

carlbman · Dec 5, 2014

Thanks for the help! I will check this out and let you know what I find.
Carl

dirt ditch · Dec 11, 2014

Just information, My 93 7753 with the BOSS system does have auto-timed glow plugs.

carlbman · Dec 11, 2014

I finally took time to study the electrical schematic. It is manual control as Dennis and Danny stated. I opened up the left side panel where the switch is and found an orange wire with a light blue tracer that someone permanently connected to a black wire. Had to stop at that time. I suspect that that is where the problem will be found. When I get it figured out, I will post the correction needed to make it right.
Thanks again for the help.