Magnum and Wiring Swap

tcanin00 said

I haven't hooked up the speed sensor to the 904 yet. The Dakota used a gear driven VSS that fit in the place of a regular mechanical speedometer drive. I would like to keep my car's original speedometer, but I also need the VSS signal for the PCM and RWAL module. I have an idea of what I want to make for an adapter to drive both, but haven't got there yet. I am open to ideas and suggestions.

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When I did my 5.9 SMPI swap on my Dakota, I was concerned that I would have to retrofit a '94/'95 Dakota IP into my '91. The '91 uses a cable driven speedo while the later IP uses a stepper motor speedo (or something similar). The big issue was that the '94 van I got my PCM out of for my swap used a 3 wire VSS and no cable pass through while my truck had a 2 wire VSS and a cable.

But then I tripped over this info. A 2 wire speed sensor will still work on a 3 wire system. The VSS pin on the PCM is powered and if you wire it to a ground through the 2 wire sensor, it will function just like it did using the hall effect 3 wire sensor. Only downside (I can see) is that the 2 wire sensor is probably mechanical in nature which means it will wear out while the hall effect sensor probably didn't have any moving parts and might last longer.

That's what I did on my swap. I just plugged in the '94 PCM to the '92 harness with the 2 wire VSS and sent it. Best I remember, the difference was that the '94 harness would have had the pin 7 8v supply feeding the 3 wire VSS while my '92 harness didn't. But the ground and signal pins for the 2 wire VSS were still connected. Worked fine, CC still works so it's getting the needed speed input.

Not sure how the RWAL works though. But removing the 8v supply wire from you VSS connection should make the 2 wire VSS with a cable work with the PCM.