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Old 11-25-2021, 12:40 PM   #1
Join Date: Aug 2019
Posts: 12
Question about Starting Solenoid Thomas 2001 HDX

Hey folks,

I have a Thomas 2001 Saf T liner HDX and I have been busy working on the inside but I may have to move it soon.

I have been having trouble with starting it from the ignition.

The starter solenoid is usually mounted in the rear electrical box, when I was doing some work it got removed from there and is hanging loose.

My question is, on this bus, is the solenoid grounded when it is bolted to the rear electrical box?

If I run a wire to the 4th pole of the solenoid to the ground terminal in the electrical box then it will start on the key, however, I am a bit confused as this 4th pole shows 12v when the ignition pole is powered?

The 4th pole is connected to a wire that goes to the rear electrical box and the wiring diagram lists this fused wire as 'ether start signal from solenoid'

I am a bit confused. Do I have a bad ground? Is this wire 'ether start signal' supposed to arm the solenoid in some way and something is preventing this?
I don't think I want to add a ground wire just to make it start from the key. Any help or advice much appreciated.

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Old 11-25-2021, 12:58 PM   #2
Bus Crazy
Join Date: Oct 2020
Location: Near Flagstaff AZ
Posts: 1,126
It sounds normal. The terminal you mention should be grounded. The case on the solenoid should not normally provide a ground, if there are 4 terminals. Just to clarify, there will be two large from the battery and one to the starter. The other two smaller terminals are for the coil, which closes the contacts between the large terminal.

If you skip to the 15:00 or so mark in this video, I start troubleshooting a solenoid like that and a bit later I describe what the terminals do. That might help?

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Old 11-25-2021, 09:15 PM   #3
Bus Nut
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Join Date: Jun 2020
Location: Long Beach, CA
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Year: 1998
Coachwork: Blue Bird
Chassis: TC1000, 40' MPV
Engine: 5.9 Cummins/B300 trans
Rated Cap: U/K
Perfectly normal to read 12 volts on the open terminal with the key on. You're just reading through the coil.
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Old Yesterday, 09:44 AM   #4
Join Date: Aug 2019
Posts: 12
Hey folks,

Thanks for the info.

That video was a fun watch!

I got things working again, I bought a new solenoid and grounded it out and now bus works on the ignition.

New problem, now none of the temperature gauges on the dash work and the display says ' no data '

I will go look for wires not connected and see if anything is obvious.

Thanks again
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