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Old 05-05-2022, 05:42 PM   #1
Mini-Skoolie
 
Join Date: Sep 2019
Location: In my Skoolie
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Year: 2005
Coachwork: Thomas
Chassis: Saf-T-Liner HDX
Engine: Cat C7 7.3L
Rated Cap: 90 Passenger
Thomas HDX No Ignition power

Okay, story time….

Spent the last two days probing and switching, crawling and cussing.

Two days ago I was headed to a Harvest host before heading south when my bus just died. Loss of power(electrical) when the bus stopped moving my dash was off.

Now when you turn the key, nothing happens. No dash, clicks, PCB indicator lights don’t illuminate, nada.

It seems to be isolated to the ignition/run/start loop.

Lights, signals work, good 12v power is getting to all the PCB/fuse/relay blocks. If I jump (fused) power directly to the ignition. It turns on/starts etc…however, my ecm is not getting good power ( likely I’m back feeding the ecm through the ignition circuit). My first thought was faulty/failed ignition switch. But it works and it’s not getting batt power.

For those familiar with HDX RE busses. There is a rear fuse/relay bus called the VEC which I confirmed is being fed good 12v power but probing any and all fuses and sockets in the unit show less than half a volt. The ignition wiring runs from this block through a switch block that it’s mounted to and I can firm that those switches work.

Why is the VEC important? Because the ignition loop goes through it. I was lucky enough to get the ign blueprints from Thomas for a previous problem. I can provide it if it helps someone smarter than me provide some solutions.

Random side note: Inexplicably the ign relay on my cabin PCB(#4) had a lose cap. I bumped it and when I did it closed the circuit and the dash comes on and the bus does it’s system checks. It doesn’t start that way but, yeah, that’s a thing.

Has anyone has the rear VEC fail and if so what were the symptoms? Additionally has anyone replaced the VEC? (Mine is bussman ser# 31174-0 )

Has anyone had a similar symptom and found a fix?

I’m stuck surfing local Walmarts in northern Utah till I can sus this out. Any help would be appreciated. Thanks in advance.

Any questions or tests you can think of, I’m all ears. Electrical diagnostics is quickly becoming my newest ‘skill’ to the detriment of my sanity.

I usually run to ‘Just Answer’ to ping my diagnostics off industry professionals but I’m not getting any responses right now, and this is now kinda problem.

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Old 05-05-2022, 07:55 PM   #2
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Originally Posted by enigmamdw View Post
Okay, story time….
For those familiar with HDX RE busses. There is a rear fuse/relay bus called the VEC which I confirmed is being fed good 12v power but probing any and all fuses and sockets in the unit show less than half a volt. The ignition wiring runs from this block through a switch block that it’s mounted to and I can firm that those switches work.
I am not familiar with Thomas busses but I would take a good look at any and all ground straps/ connections. I would go as far as disconnecting, inspecting and re- connect.

The fact that you got power of the front side but not the back side… isn’t there a B+ and B- connection in the VEC , fuse block?

Double check that B- wire/connection.
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Old 05-05-2022, 08:09 PM   #3
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Quote:
Originally Posted by ewo1 View Post
I am not familiar with Thomas busses but I would take a good look at any and all ground straps/ connections. I would go as far as disconnecting, inspecting and re- connect.

The fact that you got power of the front side but not the back side… isn’t there a B+ and B- connection in the VEC , fuse block?

Double check that B- wire/connection.
I will take a look.

There was a whisper in the back of my brain hole saying ‘check grounds.’ But it seems everyone says that and it has rarely been the case for me. (My very limited caselog)

I am admittedly NOT an electrician and I’m not pooing on your suggestion. Just rambling cause this whole thing is scrambling my brain pan.
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Old 05-06-2022, 05:51 PM   #4
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Rated Cap: 90 Passenger
Solved!

A hit of a unique case since it’s not really a problem with the bus.

I noticed that my p meter on the dash was reading +75amps. This while the bus was off and the power cutoff switch off.

This screamed short to me. I started fiddling with whatever ground locations I could get my hands on and noticed my solar system ground was loose. I reattached it checked my amp gage and low and behold… it was sitting at zero.

I grabbed my keys, said a short prayer, turned the key and bam. Everything worked perfectly. Even had better and less variable ecm voltage readings.

If I had enlisted an electrician to help me I’d be drowning in debt and still not be fixed.

Cheers all.
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Old 05-06-2022, 06:21 PM   #5
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Solved!

A hit of a unique case since it’s not really a problem with the bus.

I noticed that my p meter on the dash was reading +75amps. This while the bus was off and the power cutoff switch off.

This screamed short to me. I started fiddling with whatever ground locations I could get my hands on and noticed my solar system ground was loose. I reattached it checked my amp gage and low and behold… it was sitting at zero.

I grabbed my keys, said a short prayer, turned the key and bam. Everything worked perfectly. Even had better and less variable ecm voltage readings.

If I had enlisted an electrician to help me I’d be drowning in debt and still not be fixed.

Cheers all.

Great news !!!!
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Old 05-06-2022, 07:55 PM   #6
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say this with jamacain accent -- yea, righteous fix mon

it is always good to hear the whole story.....


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Old 05-07-2022, 12:30 AM   #7
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Good job, and it's why everyone always says "Check the grounds" any time someone has a no-juice problem. The ground is exactly as important as the positive wire.

I wonder though - if it was a solar system grounding problem, would your bus have started at night?
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Old 05-07-2022, 02:28 PM   #8
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Originally Posted by Veloc View Post
Good job, and it's why everyone always says "Check the grounds" any time someone has a no-juice problem. The ground is exactly as important as the positive wire.

I wonder though - if it was a solar system grounding problem, would your bus have started at night?
No idea! I’d love to test it and it did occur to me that I’ve bodged something up somewhere and I’m complicating my issue somehow.

Sadly this story continues and I’m once again back where I was two days ago. I’m lucky enough to have a friend with a shop nearby that I can park and dig into this problem further.

I can add one new observation, when the bus is off my amp meter on the dash read ~65amps going into the system so on the charging side. When I turn the key to on/run. It zeros out.

Normally it sits at zero when it’s off and the key going on would drop in into the - or drawing current side until the bus starts and the alternator is supplying power.
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Old 05-07-2022, 03:12 PM   #9
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bad ground somewhere.
another thread i dont remember today i read there solar ground was effecting there bus from starting.
my opinion
you should always keep your vehicle system seperate from your house system.
if you want to connect them then keep your switch mechanical and not electronic.
either way?
that would be the first one to check or replace.
until today i have never heard of a solar ground?
my renogy system did not ask for it?
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Old 05-07-2022, 03:14 PM   #10
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oops it was this thread?
sorry
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Old 05-07-2022, 03:21 PM   #11
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Engine: Cat C7 7.3L
Rated Cap: 90 Passenger
My house and chassis system’s only common is the negative lead to the chassis.
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Old 05-07-2022, 09:01 PM   #12
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Had to read up a bit on ammeters as I've not seen one on a car since I was a teenager too dumb to know anything about anything. Seems all current passes through it, except the starter. So, time for some fuse work. Pull a fuse with a helper, and have the helper tell you when they see a change. Since it's 65A I'd start with the high power fuses. When you pull one and the 65A goes away, you have identified your problem circuit. From there, it's hard slog sorting out the circuit path.

"Random side note: Inexplicably the ign relay on my cabin PCB(#4) had a lose cap. I bumped it and when I did it closed the circuit and the dash comes on and the bus does it’s system checks. It doesn’t start that way but, yeah, that’s a thing."

Before doing the fuse thing, I would start with this. Pull this out first and see if this breaks the 65A. If it does, pry it apart and look at the innards. Relays can and do fail, and it's possible for the failure mode to be a short to ground without involving the control circuit path. Bumping it that day may have cleared the issue for a short time. Or, just get the same kind of relay from a different, unrelated circuit and stick it in. It needs to be a relay unrelated to running the engine, like perhaps an air conditioner relay if they're the same. If that solves it, there you have it.
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Old 05-07-2022, 10:31 PM   #13
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Chassis: Saf-T-Liner HDX
Engine: Cat C7 7.3L
Rated Cap: 90 Passenger
Hmmm…

I agree with your premises. But, I don’t have any fuses rated above 30amps.

I do like the relay checks. There’s only a few relays on the ignition circuit.

This would help me narrow down my search. I am going to start with the battery>ground>starter>engine loop. After looking at the termination points. They are grimy to the point I can barely see them. Best to clean them up while I’m at it.
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Old 05-08-2022, 09:19 AM   #14
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Originally Posted by enigmamdw View Post
Hmmm…

I agree with your premises. But, I don’t have any fuses rated above 30amps.

I do like the relay checks. There’s only a few relays on the ignition circuit.

This would help me narrow down my search. I am going to start with the battery>ground>starter>engine loop. After looking at the termination points. They are grimy to the point I can barely see them. Best to clean them up while I’m at it.
If you were to disconnect your solar batteries, removing both pos and neg leads, does the ammeter still show 65 amps and will it start?

Just curious to know, simple test to see if there is a back feed in the wiring scheme.
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Old 05-08-2022, 01:46 PM   #15
Mini-Skoolie
 
Join Date: Sep 2019
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Year: 2005
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Chassis: Saf-T-Liner HDX
Engine: Cat C7 7.3L
Rated Cap: 90 Passenger
Quote:
Originally Posted by ewo1 View Post
If you were to disconnect your solar batteries, removing both pos and neg leads, does the ammeter still show 65 amps and will it start?

Just curious to know, simple test to see if there is a back feed in the wiring scheme.
I did, it was, and no it didn’t.

However…

I just Removed, cleaned and reseated battery cable terminals and it started right up. I hope that’s the issue… and I didn’t inadvertently effect something. I checked all the cables I could see and inspected them and there’s no rubbing or chafing that I can find.

I did before this redo the house grounding/common cable to a more secure and shorter run with heavier cable but that didn’t change the problem.
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