Power Wagon [886] Ambulance wiring question !!

I would double check condition of brushes and try a new VR.
I bought 100 amp alternator from a member said it was like new , I just installed it , the one that was taken off yesterday when idling the headlights would flicker the new one installed isnt doing that lights are stable @ idle.
VR is new - I will take alternator I pulled off yesterday and go have it tested this week just to be sure.