This harness is a must have if you have a Proto E6 and a decoder with a 9 pin plug available! It makes installation a snap, no soldering and the length of the wires puts the decoder exactly in the hollow spot on top of the weight just behind the cab. No milling or cutting needed! While it's made by TCS, I plugged it into a TSU-1000. With the solder bridge made at the factory, the Mars light works perfectly as well. It's worth the few dollars to avoid installation issues.