Just some helpful advice to anyone like me who searched this topic. Had an older Spectrum K4 DCC ready (single motherboard) and purchased a Digitax SDH167D and Digitrax DHWHP wiring harness. Should have been plug-n-play, however it shorted out when the decoder was installed. (ran fine with jumpers as DC on my DCC system). pin 1 was not marked on the connector on the motherboard and reversing the plug had same results leading me to search the internet for a solution. Didn't have any luck, but several posts here regarding decoder installation on Bachmann K4 and wanted to share what I discovered. upon looking at the motherboard, there was a solder bridge connecting the traces leading to pins 4 and 5 (with jumpers installed this had no effect on it running DC and think was manufacturing flaw that got unnoticed when tested to run as DC on DCC). Cut the solder bridge and voila! everything works fine. I am sure Bachmann is not the only company where this has occurred as DCC ready loco's are most likely tested with the jumpers and not with a decoder installed and thus such a small little bit of extra solder in the wrong place like this creating a bridge would go undetected. from now on before I install a decoder on a DCC ready loco, I am going to look at the motherboard to see if any of the soldering connections create a bridge that shouldn't be there. Hope that someone finds this helpful