Thanks Fred, I know that 60hz hum and its harmonic brethren all too well - I used to be in a very loud rock band that used excessive gain to cover up terrible guitar playing...
Regarding putting in a bus bar instead of connecting everything to the engine: For the sake of brevity I didn't explain that I have most negative wires going to what I think is the original terminal block - it's basically just two bolts (one for + and one -) set in a piece of plastic. The negative from that then goes to the motor nut. I cleaned the old terminal block up, and it conducts well, but, it's probably not a bad idea to just get two new Blue Sea terminal blocks.
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