Swapping a 5v with a 3v ps2

The easiest move will be to install the new board where the old one is.  I'm not sure why you'd want to move it, that is creating a lot of work.

If you pull the connector shells off the 5V board and slip them onto the 3V board, it'll plug right in except for two considerations.

• You'll need a 4 ohm speaker to replace the 16 ohm speaker.
• You'll need a 3V battery & charging port cable to replace the existing one.

This will be a LOT easier than moving the board and rewiring everything!  Your starter set wiring will probably not include all the lighting that the M-1a has, for instance.

The Battery leads with charging jack part number is MTH BC-1000004

Yes, you need to install in the engine.  You would need to move the black connectors off you bad 5V board and put them on the 3V board.  You also need to swap the speaker and the battery/charging harness.  You will need to get inventive in mounting the board properly.

If you want to put it in the tender, then yes you need to move both harness and battery and speaker from the 2-8-0 and install in the M-1a.  This will only give you headlight control in the M-1a and you will loose any other lighting/features.

If you don't want to attempt this I can repair the M-1A.  G

George, good point about moving the battery harness and speaker from the donor locomotive, might as well use it.

You need too since MTH doesn't sell the BC-1000004 anymore, you get referred to the 3V hardware kit which has speaker and battery too.  G

Well, that would work, but since he already has it, clearly it's a better move to simply use what he has.

Wasn't there a charge port for the battery in the tender of your M-1a? G

True early 5v PS2 did NOT have charging ports.  And if you add a BCR you will not need one.

Ok,  You don't need one for battery either.  The battery is in the tender, so you can splice in the new connector from the 3V engine to the battery wires in the old tender.  Make sure you get polarity correct.  + to +.   G