Lets start with the SW. first. Did the decoder have dropping resistors for the LEDs? Are these hardwired installs or plug in? If it is a plug in decoder turn the plug around and see if the lights light.
The GP sounds like it may have a stray wire strand or even a motor that has grounded to the metal chassis.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
"& that the decoder had an internal resistor for such an install."
From NCE I basically use the DSAR decoder. It has a resistor on board for use with an LED however there is a "trace" on the board that needs to be cut in order to activate the resistor. The trace by passes the resistor or short circuits it. I don't know if that is the same with the decoder you are using. Just passing the information along.
gondy529I installed NCE decoders in Proto 2000 SW8 & GP9. Also replaced lights ( LED in SW8). The SW8 runs fine, but no lights work. The GP9 works erratically. Put Kapton tape on underside of decoder & made sure wires were not pinched, but after placing it on programming track, and then on layout, it runs, but at a steady, uncontollable speed ( does not respond to any of the cab commands). Tried reprogramming it several times; sometimes it works, other times just the steady speed. Light in that loco does not always work. Any suggestions would be greatly appreciated.
Set CV29 to 34 and see if it fixes your problem. This turns off the DC mode support. It's a pretty common problem to have a loco take off on it's own with DC mode support turned on and might be what you're seeing.
Springfield PA