1997 mountain aire diagnostic plug

As you can see we have an older coach. The diagnostic plug under the dash is a rectangular one that has many holes but only 4 connector pins/wires. Is there an adaptor I can get to use with the VMSpc? If so, where can I get one?

First, which engine do you have?

If you have a 1997 coach and this is a Cummins C-8.3L engine (usually 300 or 325 HP), then you have a mechanical engine and can't use VMSpc. If you have a Cat, the 275HP ISB, or any of the big Cummins engines, you are electronic and good to go.

But . . . if this is a Freightliner chassis you may not have a plug at all. Freightliner wasn't too quick about getting their chassis wired for the electronic engines, and roughly the first year's production went out without the plug. If that's the case you aren't out of luck though. That rectangular plug you found will do the trick.

Except . . . there is no adapter available. That's a proprietary Allison ALDL plug, and they never released the design to allow other companies to plug into it. If you want a mate you pretty much have to buy an Allison service tool and cut off the end.

But . . . that isn't the end of the matter. If you get yourself four Scotch-Loks, you can tap into those four wires in about four minutes. It's not as clean of an installation, but it's simple and only takes a pair of pliers. The VMS 200 Installation Manual on this web site has the pin descriptions you'll need.