Hello.

When installing the new motor, the Märklin instructions show to add the soldering tab to the motor shield and attach the ground wire to it. Now on the loc I’m converting, the wheels on that bogi with the motor all have tractions tires. Won’t that prevent that bogi/motor from being grounded? Should I attach the ground to something else, like the frame? Or connect ground in two places? Or is it fine on that motor/bogi?

Thanks.
Model in question is the 3165 Marklin 3165.pdf (120kb) downloaded 42 time(s).

Hi Norbert
On the very common Märklin locos with 2 bogies like you seem to describe normally:
- the front bogie has a slider with a cable and the 0 is conducted by two metal supports from the bogie's frame rubbing against the loco frame.
- the rear bogie has a motor and 4 traction tyres and is not connected to the ground
- Märklin advice is to increase the number or ground returns: one is to do exactly what you mentioned (a soldering tab on the motor connected to the chassis).
- another one is to connect the metal chassis of the front bogie with the frame chassis using a thin and flexible wire.

When locos are brand new, all this is an overkill but with the years, corrosion and dirt it becomes very useful
Cheers
Jean

Thanks for the answer. When I add the additional ground would I splice a wire together with the one from the decoder or do you add an additional wire to the decoder then to the frame? Thanks again!

A lot of very good advice from bph.

I think most of us sort out the hot side of the circuit when there are current issues, but in the end I usually find that the problem is in the return, not in the supply. I routinely beef up the ground options every time I rewire a loco anymore, unless Marklin beat me to it. It almost always improves running and reliability.

I have had similar problems in the grounding of the chassis to the tracks in the BR 120 locos. Hesitation of my locos happen also when grounding is not good. I have found also adding 3 oz weights also help. Heavy loks have better grounding connection.

What I have done is (some people may call this extreme, but it works for me). I have a brown wire, strip the wire about 1 inch. Twirl the copper wires together, put a very small amount of solder on the end to make sure all the thin copper wires stay together. Then I coil it around an axle in the boggie that has the shoe, about 3 coils and all the wire is coiled. Push the other end of the wire thru the hole where the shoe wire (red and usually black)goes up the chassis. Then I connect the brown wire to a screw that screws to the chassis and so it is grounded. This way you are assured your wheels are grounded.

I have noticed in the later models of the BR 120, Marklin has added a three prong spring that is screwed to the boggie screw and touches the bottom part of the chassis and the 3 prongs rub on the chassis. Some of the earlier models do not have this feature.