Had a great hunt last week and had to share it. I know we have all had the misfortune of trying to hunt down a green booger in a wire. We had a 2014 KW in the shop missing the RT Rear turn signals and brake lights. KW and PB trucks now incorporate a central electronic control module and a solid state device called a chassis node.
There are at least 10-12 fuses that supply power to both units and after we verified we were missing power at the chassis node on one pin the hunt was on.
We had a more or less dead open wire. Showed OL with an ohm meter and it wouldn't light a power probe green or red light. But I would register about 40mv at the chassis node connector. It had a good 12v supply from the fuse box. With a meter in the node connector and a guy watching it we started wiggling the harness down to the node connector. Sure enough as we got close to the green booger we started seeing the voltage jump around getting as high at 300 mv. It's not much but it was enough. We got it narrowed down to 1-2 feet of harness before we lost the reading on the volt meter ( we broken the wire ). Ripped open the harness and found our little green friend.
We have seen time and time again how unloaded circuit voltage testing can bite us in the butt. In this case it saved ours. The green booger was such a large resistor it was killing all but 40 mv to the end connector. A loaded circuit would have shown a full 12v drop with nothing left over. Another tech had said "have fun finding it, just put a harness in it". Well I did have fun finding it and showing my padwon a new trick.
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