Older Märklin Locos have a mechanic reversing unit. As a rule, most of these locomotives have no light change - the lights are alwasy burning at both sides of the loco. Nonetheless, there are some old engines where every lamp is lighted with an own glug-in bulb, and particulary those engines have a light change.

You have the possibilty to convert a light change. For this, you have to do some changes of the wiring.

Wiring Plan A Wiring Pan For A Locomotive In Original State

Now we look at wiring plan A. It is showing us one of these above mentioned locos with its original wiring. The mechanic reversing unit has two electric connections, which are described as A1 and A2 in this plan. From thgese two connections, wires D and C are leading to the field coil. Wires E and F, the connection wires for the lamps, however, are soldered at the left brushes' holdering (No. 7, on the wiring plan). Also wire A, the power supply from the pickup shoe, and wire B, which suuplies the reversing unit with electricity.

Wiring Plan B Wiring Plan For A Loco With Light Change

For receiving a light change, wires E and F have to be soldered at the connections A1 and A2 of the reversing unit where wires D and C are already connected.

On Wiring Plan B, the wire E is soldered at A1, together with wirel C. Wires F and D are soldered at A2.

However, for every locomotive you have to check it yourself what of the two wires D and C (the two wires leading from the reversing unit to the field coil) is used for forward an what wire for backward running. When you have find out this, you can solder the wires E and F at A1 oder A2.

When soldering, please bne carfeful that wires D and C don't come loose. For the case that the old ones are too short, you also have to provide lines E and F with new wires. Wiring Plan B shows the changed wiring.

Tip: When you are soldering at the reversing unit, please work vey carefully! The frame of this relais is made of plastic, and you certainly know the typical charackteristics of this material when it gets too hot!

Of course, you can only do this change when the loco is lighted on both sides. At some older steam lokomotives from Märklin, the lamps of the tender are without function. Also note that at some locos, after the change, the lights aren't anymore as bright as before. Also regard that the lamps are still flashing after the change. this can only be eleminated by exchanging the mechanic against an electronic reversing unit.

Disclaimer. I can NOT be held responsible for any damage you cause by following my instructions, on modifying your model railway equipment. Everything you are doing, you are doing it at your own risk!