Power Wagon [886] Ambulance wiring question !!

Update - installed 100 amp alternator I bought from a member and battery stud was bent pretty bad glad seller mentioned this [NOT] !!
Well after installing alternator amp gauge still bouncing around at idle was getting dark so pulled headlights on and gauge smoothed out and was normal and headlights were good not flickering at all !!!
When u cut headlights off gauge starts bouncing and light in amp gauge flickering you think that China made voltage regulator from
Advance is marginal ??