TMC MC9 Wiring

AKThom · July 31, 2007, 02:03:24 AM

Hello all, I am finally getting around to work on my bus. One of the things I have discovered (thanks to all your posts here) is that it is a TMC MC9 manufactured in April of 1981, with the VIN # ending in BR002635. I am looking for some kind of wiring diagram for the 12V system. The former owners told me that the bus had a problem and no one could figure it out etc. etc. and it would take a thousand dollars or more to trace it out. Sounds like a lame story to me... Their fix was to install a 24v to 12v converter, wire it to the fuse panel and call it good. Is this normal and an acceptable fix? I'm not really inclined to think so, but I have been wrong many times before. Do the TMCs have the same wiring as the early MC9s and are there any manuals still in print?

Thanks
Thom

Hi yo silver · July 31, 2007, 10:47:55 AM

Tom,
I have some of the electrical schematics for 9s. I don't understand why the prev. owner would do what he supposedly did. Doesn't seem like a logical approach. If you want, unless someone with more expertise chimes in, give me a # and the best time to call, we'll discuss it some more.
Dennis

AKThom · July 31, 2007, 01:18:55 PM

Thanks for the reply Dennis, I didn't think there way was the right route to go either. I'm new to the bus world so I wasn't really up on the industry practices. There is a converter bolted to the wall of the front luggage bay with a cable going through the bulkhead to the battery compartment, and then the 12v feed goes off into the wiring harness back in the battery compartment. Call me any time 907-715-6655. I'm currently in Alaska trying to get our old house remodeled for sale, then I'm on the road to AZ.

Thom

P.S. This goes out to everyone... Is there a bus friendly route through Canada? I would like to go Yukon, BC, Alberta, then drop down into Montana. I would like to stop into a few bus shop along the way if possible and maybe pickup som of the little goodies my MC9 is missing.

prevost82 · July 31, 2007, 02:24:11 PM

If you head over to Edmonton from Dawson Creek it's pretty flat, then down to Calgary and into Montana but you have to get back over the rocky's somewhere. Maybe from Dawson Crk to Prince George down 97 to Cache Creek then down hwy 1 to Hope, no real long or steep grades, then hit I-5 down to I-10 into AZ.
Ron

Stan · July 31, 2007, 05:34:49 PM

Thom: Most buses that use a 24 volt system only have 12 volts available for things like PA amplifiers and video players. The older buses just ran a tap of the 12 volt connection between the batteries. Later models used a Vanner (brand name or equivalent) equalizer. This is an electronic device that maintains the same voltage on both batteries if you are using a lot of 12 volts.

Is there any chance that this is what you have?

AKThom · July 31, 2007, 09:08:48 PM

Well I, will have to go and double check Stan. I am sure that the device says right on it 24v to 12v converter. The former owners told me thats what it was for, they had it installed because of their wiring problems with the coach. It seem the logical way to get 12v from the system is to tap off the positive side of the battery that is the one with the ground cable. If you come off the other batteriy the your into the 24v side.

Thom

Stan · August 01, 2007, 12:34:12 PM

Thom: If you use any significant amount of power from the 12 volt tap, you will quickly ruin your batteries on the charge cycle. The Vanner equalizer draws power from both batteries and keeps them balanced on both charge and discharge.

There is nothing wrong with using a 24 to 12 volt converter to supply 12 volts but cost is usually the reason people don't use them. The common Vanner can source 60 amps at 12 volts and a 60 amp 24 - 12 converter is pretty pricey.

Hi yo silver · August 01, 2007, 04:06:43 PM

Thom,
I copied and mailed the MC9 schematics and terminal board diagrams today. I hope they'll be some help.
Dennis

Sammy · August 01, 2007, 04:49:58 PM

Try Nimco in NJ for a used Vanner battery equalizer.

gumpy · August 02, 2007, 04:22:51 PM

Your MC9 would have had a center tap which was routed to the A/C junction panel in the front bay, and from there, it would have been routed to the front and rear junction boxes. The rear junction box route was optional. I think the front was standard. There should have been a headlight relay in the A/C junction box, also, which utilized the 12 volt system, but not sure if that was introduced as early as your unit, or if your's might have had 24 volt bulbs in the head lights.

I'd recommend you remove the converter and fix the center tap system. You could consider installing a vanner, but if you're not adding much for 12v loads (maybe a radio or two) you shouldn't have any problems with imbalance of the batteries. However if they bastardized your headlights to direct 12 volts, as is often the case, you'll need to address that, also.

craig

AKThom · August 03, 2007, 04:27:46 PM

I just got off of the with the old owner.... and heres a new twist, hes not sure is on this bus they had it installed for the REI video system, or do I have the bus with the messed up wiring ARRRRGGGGG!!!! I'm gonna have too start over and trace out some wires. Wish me luck Guys "I'm going in"

Thom