Wiring for older (1996) Bachmann Plus B30-7 Loco

[JEL1948]

Does anyone out there have a detailed wiring diagram for this 'old' loco? I have the exploded diagram that came in the box; the wiring is difficult to interpret from the diagram. I'm installing a decoder. It appears to me that the positive side of the motor is the top terminal. The connections on the trucks have me stumped....what is the purpose of the D-loop wire on the outside of each truck?.....I'm trying to differentiate between the left and right rail connection on the trucks... one loco truck has a red lead/the other a black lead. Wires to the trucks go to both sides of the trucks, meaning wipers electrify all four wheels on each truck. Any ideas about which truck should be wired(for the decoder)to left rail connection and which for the right?
Any help would be appreciated!

[rbturner]

Do you have a voltmeter? Using one will quickly help you trace the wires.

Generally, the engineers side is positive. The 'right' rail is positive. The 'left' rail is negative. The standard wiring code for DCC is right rail red and left rail black.

But Bachmann (and others) have used whatever color they wanted. I have seen them use both colors together.

As for the motor, if you can figure out which pole the right rail fed, that's where you want the orange wire. Of course the gray goes to the other pole. Be sure the motor poles are not touching the frame anywhere.

[Len]

You will quickly find in model railroading the multimeter is your friend. Whether it's using the Ohm meter function to trace wires, or the voltmeter function to verify power is getting where it's supposed to or not.

If you don't already have one, you can get one for less than $25 at most hardware stores and home improvement centers.

Len

[JEL1948]

Thanks for the responses. Here's the problem...rather than 2 wires coming from each truck there's only one...normally one wire would be the fireman's side/the other the engr's..simple..but on this loco its not so.

[Len]

Sounds like you may have a loco with a split frame and the side of the trucks without a wire is passing power directly through one side of the frame. The easiest way to check is with the Ohm function of a multimeter. If you get a short, or very low resistance, reading between the wheels without a wire and one side of the frame, it's a split frame set up. If that's the case, you'll have to isolate the side of the motor connected to the frame in order to install a decoder.

Len

[JEL1948]

Len, you're right on. Upon careful inspection of the motor and the trucks/wheels I've concluded that the right rail motor connection runs through the frame. So I will isolate the motor from the frame and connect new wire to track/wheel wiper (right side) and sever the "D" or loop connecting the right wiper to the frame. That ought to clear the pathway for the decoder to work as well as isolating the motor/frame/wheel connection!
Thanks for your help.
John L