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Old 04-10-2010, 06:26 AM   #1
dentedvw's Avatar
Join Date: Jul 2009
Location: Lansing, MI
Posts: 236
Year: 1998
Coachwork: Thomas SafTLiner
Chassis: FE
Engine: 5.9 Cummins
Rated Cap: 60
Need help from owners of Thomas buses, mid nineties

I have a problem with the switches that control the heaters in the dashboard. I am certain it's due to improper wiring of the switches. Problems is, there is about a thousand ways to connect these dang ol' wires, and it leaves me with no options other than hours upon hours upon hours of troubleshooting that would likely leave me no better off than when I started.
Luckily for me, there is some commonality among these buses. That's where you come in. The HVAC panel (if you can call it that) on the dash is pretty common among these buses, and the wires are color coded, somewhat. It's held in with four screws, and tips out pretty easily, though only far enough to access the wiring.
It would really, really help me out if someone, or even better a few people, could take a good picture of this unit tipped out of the dash, it would only take a few minutes, and it could help me out immensely.

My trouble is that my switches work only in the wrong positions. One of them works only on low, when the switch is in the off position, and the other only works on low when in the low position, I think. Something like that. It's wrong though, that's for sure. It got mighty cold on our trip to Texas last week, but we stuck it out with sleeping bags, sometimes having to drive while inside one. I tried a few combinations, but never got an improvement, and when I would tip it out of the dash, some wires would inevitably fall off. I need to crimp them a bit tighter, it seems. I can do that, but no point until I know I have the right combo.

You can see it there, beside the gauge part of the dashboard, next to the spaghetti system of temporary power cables to the GPS units and XM radio. Two rocker switches and three stiff sliders that do almost nothing.

So, whattya say?


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Old 04-10-2010, 10:26 AM   #2
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Join Date: Apr 2010
Posts: 1,485
Re: Need help from owners of Thomas buses, mid nineties

id almost say replace the rocker switch and see what happens.
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Old 04-11-2010, 07:12 PM   #3
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Join Date: Jan 2010
Location: Northeast CT
Posts: 201
Year: 1999
Coachwork: AmTran RE
Chassis: International
Engine: T444E
Rated Cap: 72
Re: Need help from owners of Thomas buses, mid nineties

The switches have 8 terminals on the back. If you look closely, they're numbered:

8 7
1 4
2 5
3 6

7 and 8 are for the panel lights, 8 positive, 7 negative.
5 is +12V from the fuse (usually a white wire).
3 is low, 6 is high (not sure which colors, high may have a black tracer).
1 is not used (except for a "park" wire in wiper switches, it's hot when the switch is in the down position).
2 and 4 must be connected by a jumper wire.

The jumper wire is the important one, without it you'll never get the switch to function right on both high and low. If you're good with wiring diagrams, check out ... itdiag.pdf to see why. These switches use circuit E.
The conversion of Miss Euphegenia, a 1999 AmTran RE:
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Old 04-28-2010, 04:30 PM   #4
dentedvw's Avatar
Join Date: Jul 2009
Location: Lansing, MI
Posts: 236
Year: 1998
Coachwork: Thomas SafTLiner
Chassis: FE
Engine: 5.9 Cummins
Rated Cap: 60
Re: Need help from owners of Thomas buses, mid nineties

Ok, I have been fooling around in there, and still can't get it right. This is what it looks like. I am going to flip your diagram, because when I pull the panel out, it is in this orientation for me.
6 3
5 2
1 4
7 8

The picture below is what it looks like in real life. The switch on the right is the dash fan/heater controls, the left is the defrost fan/heater.

I tried it your way, and nothing turned on. Dang ol blasted thing.
When we were buying the bus, it had this same problem, and the mechanic popped the panel, I didn't see what he rearranged, and then it worked normally. I think on the drive back, or some time shortly after, it wasn't working, so i popped it, and a few wires had fallen off. Now, a smart person would have smashed the terminal a bit so it would STOP falling off, but that guy was just in a hurry, I will presume. So, there is a few off. I don't think much of it, and plug them in where they were nearest. I didn't pay any attention to which they were, and any attempts to recreate the falling off are prevented by my having mashed them so they wouldn't do that. So, now I don't know which are wrong, but by your diagram, it would seem a lot more than I remember having fallen off. I am remembering it was only two or three wires, and only on one switch.

So, maybe we could get a couple of folks to chime in here, hopefully with either a picture of theirs, or a description using either your or my diagram.
FWIW, the extra yellow wire with the crimp cap is something I added for the illumination wire of the radio. I put a meter on it and watched it go up or down in concert with twisting the light knob on the dash, so I am somewhat certain it's correct.
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Old 05-03-2010, 10:27 AM   #5
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Join Date: Mar 2010
Location: Shoreline, WA
Posts: 176
Year: 1998
Coachwork: Thomas
Chassis: International
Engine: 7.3L, International
Rated Cap: 35
Re: Need help from owners of Thomas buses, mid nineties

I had a similar problem in my Thomas, fan would only work in low, no high. I bought a new switch and the problem went away. ... egoryid=48

The switches I think cost around 18.00- 26.00 bucks apiece but it solved my problem.

Good luck

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