You may have already done this, but sounds like you have a short in the vec of the sender, i have another years wire harness on mine and sometimes the connection comes loose which causes exactly what you say kinda waves around for awhile reads right then wavs ETC? Additionaly if it jumps into the red zone its hitting the block, when my wire falls off and lands on the block it jumps into the red because its ground out.

So id check the wire harness , cut her open and see if you have any bare wires showing inside that could be causeing a short.

Jason

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