I would just grab a 12V power supply or separate battery to temporarily power the MC050 and expansion unit. Be sure the temporary 12V power to the MC050 and expansion unit is isolated from machine 12V, but connect the temporary supply's negative side to the machine negative. That would rule out or confirm that you have a power issue.
Personally, I almost always put a decent DC-DC converter between the vehicle power and any Plus+1 system, even on 24V systems with a lower percentage droop. Too many problems with both dips and spikes.