I only have a small inverter that I turn on when needed; it wasn't even wired in when I was testing. I just use the standard regulator on the alternator which was switched out with the alternator. It could be my meter but it only shows the ripple with the engine running below about 2000 RPM so I doubt it.

Any idea if a leakey ignition coil could cause something like this? The engine starts and runs fine so I'm not convinced this is the real problem.