wire to motor

[RAM]

I have a replacement motor for one of my 2-8-0s.  I was getting ready to replace it today. I
noticed there is a red dote by one of the posts.  I just wonder if the red wire should go to that
post.  It is not wired that way. 

[Yampa Bob]

A red dot denotes positive, but wire it the way it worked before. Wiring in locomotives and tenders seldom conforms to color code convention.

If in doubt you should check the motor wires with a multimeter before soldering, and confirm proper rotation before assembly. 

All my Connies have orange and gray wires and the motors are not marked for polarity.

[richG]

The red mark on the motor is for plus voltage with minus on the other for forward on the loco.
NMRA indicates black and red for rail pickup and want a different color for each connection so the NMRA uses Orange for the plus lead on the decoder. Grey for the minus lead.
When the locos is used as DC only, the color code of red and black applies directly.
Add the decoder, things change.
I have seen the red lead called motor right also.
The motor armature will turn to the right and with compound gear reduction, forward motion, at least for steamers.
It is the same direction  for Spectrum and Roundhouse steamers. My Spectrums, the top motor lead is the positive one but are not marked with colors. The wires going to the motor terminals are colored but covered with some kind of black coating. I will not even mention what those colors are as most people do not open their locos.

Even with the color code, some people still manage to wire their locos incorrectly and burn up the decoder. Many things change between DCC and DCC and a few people have difficulty with that.

Something all model railroaders should be aware of. The person in the article belongs to one or two Yahoo DCC groups.

http://www.siliconvalleylines.com/dcc/2008/DecoderHW.pdf

Rich

[Yampa Bob]

A permanent magnet DC motor has no electrical "polarity", only the magnetic polarity of the internal magnets.  In other words, the motor has no specific positive or negative terminals.  Read on please. 

By convention, shaft rotation on small permanent magnet motors is stated as viewed from the brush end (rear) of the motor, either clockwise (CW) or counterclockwise (CCW) rotation.

The presence of a red dot or plus sign on a new motor simply indicates that the positive lead connected to that terminal produces the rotation as specified by the motor manufacturer or the factory producing a motorized device, typically CW, but may be CCW depending on the maker and the application.
 
The Spectrum 2-8-0 uses direct drive. By that I mean there is no intermediate idler gear.  The worm gear is "right hand", just like a right hand thread on a bolt, and since the motor is positioned with the output shaft to the loco rear, the shaft must rotate CW for forward motion.

If a motor is positioned with the output shaft forward and is direct drive, then the shaft will rotate CCW for forward motion.  (So far I have found no markings of any kind on my Connie motors.)

Bottom line, wire the motor to achieve proper shaft rotation. If loco direction is wrong, then switch the wires. Here is a flash animation everyone should view.

http://www.mabuchi-motor.co.jp/en_US/technic/t_0102.html

Why the confusion?  Using a decoder as an example, the orange wire is labeled "Motor Plus".  The "plus" is not referring to the motor terminal, it means "this is the positive lead..... connect it to the motor terminal that results in proper direction." 

Moral of story, don't assume anything, use your multimeter to confirm all wiring polarities, and confirm proper direction before re-assembling any loco. It's no fun installing a new motor twice, better to get it right the first time.

[pdlethbridge]

Ya, but do I REALLY, REALLY need a multimeter? I installed lots of motors without one. In testing I always killed the power before the smoke got too bad.

[Yampa Bob]

Just for installing motors, probably not. There is a 50-50 chance of getting it right the first time. If the motor is completely isolated (and it better be if running DCC), then the worst to happen is that the loco runs the wrong direction. So if you don't mind taking the thing apart again, switching the wires, replacing the t-nuts,etc....

However, considering all the other troubleshooting tasks, it just makes sense to have a meter.  Notice I edited my post to say "use YOUR multimeter". 

[pdlethbridge]

I think all decoders have a cv to reverse the direction of travel if you get it wrong. Otherwise just turn the loco around to get it right.