Try terminating the unused test points, in particular the rev test points. It could be a lot of things, I chased the beacons on my truck for 3 hours one day until I forgot to turn them on when I pulled up to a pole, I was up sweeping, in a good mood because the spikes were gone, until the boss pulled up and chewed my ass for not having the beacons on, he flipped the switch and the spikes came back, I yelled at him to turn them back off and the spikes went away. Didn't have to use my beacons the rest of the job. We tore out the ADC nodes here due to problems like you're seeing.
Never argue with an idiot, they will drag you down to their level and beat you with experience. Winston Churchill
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