Over the weekend I had some difficulties with the PMD extension harness. This is the 40" extension that comes from JK. I purchased the PMD, cooler and harness from a local guy that was parting out is truck. All of these components have less than 15k mi on them, and were working fine when removed - I verified this.

When I put the harness in, regardless of which PMD I use (my spare or the one that came with the purchase), the truck does not start. Take the harness out, connect the PMD(s) to the connector that originally went to the pump mounted PMD and all is OK. Is there something that I'm missing? Someone elsewhere mentioned 'stacked resistors'. Is there a resistor in any part of the harness - original and/or extension?

Have you checked continuity of each of the pins on the extension harness from one end to other? Any of them shorted together?

My "store bought" extension is wire mated to two GM female connectors then one end has little pins sticking in the female to make it a male connector. Is one or more of the metal "pins" not making a good connection? It was a plug and go thing for me hardest part was unplugging and fishing the end that mated to the OE pump mounted FSD.

Well... that is one of the concerns with having a really long remote harness. When you start running electronic signals down really long wires (40", 72", etc.) you can start having issues with the wires themselves becoming part of the circuit. The wires themselves can have inductance, capacitance, and can produce impedance mismatches, etc. The net effect is that the electronics may not work.

Nonetheless, I suggest you check the harness using a multimeter to see if the harness has electrical integrity. That would be a first step. If it doesn't it is probably a problem with the connectors, perhaps caused by pulling them apart. 90% of all electrical problems usually deal with faulty connectors.

Sincerely,

Rob :)

Ran a continuity check on the harness. Everything was clean from end to end. Called and spoke to JK since that's where the FSD cooler and harness orginated (wasn't sure he was back from Montana when I originally posted this).

John mentioned a 'coupler'. I have no 'coupler', just the female end of the truck wiring harness, and the extension with a male and female end. With that said, John told me to connect the extension to the truck with the 'latches' opposite of each other and to make sure that the male pins were securely in the extension harness. He also mentioned that the coupler also 'flips' the connectors.

Upon further review, I did see that the truck harness, and the male end of the extension do have the pins labeled A thru F. When making the connection with the 'latches' on the same side, the pins end up being crossed. With the latches opposite each other, all is well. I had been connecting the harness with the latches on the same side.

I think I'll order a coupler. To me it will serve two puposes - one, avoid confusion as to how things connect, and two, it provides a weather seal for the connection. Right now I have it wrapped with electrical tape.

Properly installed, all is well now, and the PMD is mounted up front in a cool air stream.