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stiltdancer 08-28-2018 08:39 PM

0 Volts at Instrument Panel, Bus Cranks, Won't Start. Thomas HDX
I messed something up on my build. ugh.

I have a 2005 Thomas HDX pusher with a C7 Caterpillar engine and an Allison 3000 transmission.

The engine cranks but won't start. The voltmeter in the instrument panel used to show ~12.7 volts, now it shows 0.0 volts. I'm assuming an open circuit, but have no idea where that voltage is measured at. It would give me a great start for troubleshooting.

I've been keeping the starting batteries charged at 100%, and noticed when it's going through the start routine after turning the key that "1_1.1" shows up on the panel. I'm not sure if that's new or not.

There are no engine or transmission codes. When I tested all the fuses I found a 5A accessory fuse blown.

I've been coloring all over the wiring diagrams, but have no idea where that voltage is measured.

Do you have any ideas for me?


ShagNasty 08-29-2018 02:54 PM

I believe that I experienced the same problem. When you turn the key to the on, not start position are you getting any indications of the wait to start or warming up Glow plugs.

I have a 2002 Thomas and when this happened to me it drove me crazy to the point of scrapping the bus and curling up in a corner and pouting.

Inside the Electrical compartment under the Drivers window (My Bus) don't know where yours is. There are two Solenoids, one is called "Body" and the other is called "Chassis".

The purpose of those are when the key is in the on position Voltage is transferred thru them to the various parts of the vehicle. Body solenoid is for all the accessories and lights, and the Chassis is for all things related to starting the Bus i.e. ECU, Glow plugs, Intake heater and initial ECU Diagnostics. :thumb:

Check to see if when your key is in the on position that you have voltage between the two large posts on the solenoids, if not check to see if you have 12 volts to the center post when key is in on position. If you have 12 volts to the center post and nothing on the outlet of the solenoid then you have a bad solenoid. Also you should have continuous 12 volts to the inlet of the solenoid and if not trace down stream and check for fuses.

Here is a picture of what I hade to replace. Amazon $55.00 bucks.

White Rogers 100 Amp Continuous Duty 3 post Solenoid

Attached Images

Smokey's pipe dream 08-30-2018 09:16 PM

think that solenoid would work for charging my house batteries so i wont run down my start batteries it Should shouldnt it? is it stout enough?

stiltdancer 08-30-2018 09:53 PM

Thanks for that tip - it's pointing me in the right direction! It's so frustrating.

On my bus there's a solid state master circuit (that was the result of a recall). I had no idea there were 3 12v systems on the bus. One runs right off the battery for the engine (that's why it cranks). Then there's Body Electrical and Chassis Electrical. The master switch is driven by a Body Electrical Ground and a Chassis Electrical Ground. I think one of these is messed up.

I started poking around in PCBs 1&2 with a volt meter. It had some frustrating results.

With the key off I checked the voltage going into every fuse. Some were 13.4, some were 0.0, and a few were either 0.1 or 0.4 volts.

With the key switched on I was mostly getting readings from 4-7 volts, plus some near zero voltages, plus some 13.4. So I think there's some electricity leaking into the grounds, and a short or corrosion someplace.

The last thing I did was check the rear electrical box - and there's a lot of corrosion. I pulled the green and blue connectors off the VEC to check them, and they were really stuck on. One had a pin that had melted all the plastic around it. The other had a pin that broke off and had a lot of corrosion.

Tomorrow I'll do more poking around in there and print up some more wiring diagrams.

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