looking for a ford tech or someone that has worked on a 1993 ford ranger starting

[Chev M]

problem? son bought a 1993 ford ranger battery light would flicker on now on constant so replaced battery, alternator and starter still has battery light on measured volts at alternator only putting out 2.5 they had the yellow with white stripe as a ground but found out they cut wire to alternator that has power so re hooked up now battery light goes out but starter stays engaged when started i checked all wires nothing seems crossed or shorted where would the most likely problem be cause im stomped even being a gm tech for 20 years any help would help also with wire disconnected starter will disengage but battery light comes on steady and truck runs off battery till its drained