I have the split gear problem on my Gp 18, so while I have it open I thought about converting it to DCC. Looking at My wiring it appears I have an older version without any circuit board. It looks like the Motor and the lights are wired in series with a 6 pack of resistors to control the step down for the lighting. This would mean that the motor would be running at about 6v. . To install a DH123 I would need to mill out the top of the weight over the motor about 3/16" but how would you wire in the motor and the lights.
I’d say you are better off with a DA series Decoder from NCE. And don’t worry they do run with Digitrax. All 25 of my locomotives have them and they run perfectly fine with my digitrax system. But the NCE chip is a lot easier to install and they can be put into any locomotive. It already has a place for lights. It would probably take you 20 minutes at modt to install. Think about. Plus for your cracked wheel problem, Go with Athearn wheels. They slip right in, and there vertually indestructible.
Happy railroading[(-D]
James
I have wired an old P2K GP18 for DCC using a Digitrax DZ-123 decoder. The light pack is a group of diodes which a-make the headlights directional and b- keep a constant 1.5 volt to the lights when track voltage is high enough. I removed the diodes and the lights, and the space left was just large enough for the z-scale size decoder. They cost about the same as comparable DH’s, and you won’t need to mill the weight.
When removing the diodes, cut the wires as close to the diodes as you can. One blue wire will be connected to the large weight around the motor, this is the right track pick-up (assuming the short hood is front) which connects to the red decoder wire. The two left track pick-up wires run from the tops of the trucks to the top of the motor. I cut the front one (red) at the truck and used it for the motor lead (gray on the decoder). The rear lead (black) I cut at the motor, it and the wire which I added to the front truck connect to the black wire on the decoder. The last wire, the yellow one, is the other motor lead, which connects to the orange decoder wire…
On the decoder, I first cut down the wires to about 3/4 inch long. I soldered the scrap length of black wire to the front truck for track power pick-up. Very carefully strip 1/8 inch of insulation from each wire on the decoder and on the locomotive (I used my fingernails). I connected the wires by holding them next to each other and twisting the wires with my finger, then folded the wires back over the insulation and wrapped them with a small piece of electrical tape. I normally solder connections, but there wasn’t room for it in this case.
I replaced the lights with 14 volt grain-of-wheat bulbs, since there is no room for a resistor to drop voltage. One wire from each light connects to the blue wire on the decoder, then the other connects to the white for the front headlight, then the yellow for the rear headlight. At this poin