85 4runner charging problems

[krackem]

My truck has started to not charge the battery and volt gauge it stays around 11volts, and will not start a new battery after 3 hours riding . Ive checked fuses(good)alternator (good) but the low volt light in the cluster don't work (checked bulb and also good) but do sent come on with key in on position. Boosting off and at first alternator. Put 14.5 volts out then falls I quit reading at 8 volts, anyone got any ideas on where to start lookin for a problem or what the wire should read on a volt/ohm meter

 

[krackem]

OK bought conversion bracket from t.g. and got a gm alt.(thanks sprdave) its a 12si with threaded ear at 9 o'clock but I confused on if it isn't or is a 1 wire. To much conflicting info can some one help me figure out do I need I wire or 3 to make it work , cus its got the 2 male prongs at 12 o'clock. All the good write ups I've found show using three wires I'll post a pic later today of alt. I'm probably making thiw s harder than its is but damn I thought it was disposed to be easy