Alternator or external regulator issues 83 22r

[83 Ranger]

I happened to look at my solar charger display hooked to my coach battery with no solar panel connected and the meter said 17 volts with no dash light on, engine running it works light goes out as soon as engine starts  Checked both battery voltages with meter and were at 17 volts shut it off immediately Checked all wires checked all connections and grounds everything's fine I purchased a new voltage regulator and it read 15.5 volts Took it back and got another one This one reads 13.01 at back of alternator + terminal  battery voltage reads 12.87 with engine running Can't imagine two bad voltage regulators in a row and I took alternator to parts store they said its weak but still working within specs Sensor wire has 12v ignition wire has 12v on alternator What could be the problem?  

 

Thanks in advance 

 

[extech]

how old are the batteries. as they sulfate they can show a charge above 15volts

[83 Ranger]

Coach battery 2 id 9/19 not sure about the starting battery?

[extech]

so....  turn on headlights for 5 min,   now check starting bat.  what v.   should be 12.6 for a good bat.  higher not bad. lower- need new one.   the charge at 15.5 isn't out of line.  

[83 Ranger]

I did that and appears my batt is still good held at 12.6 Diagnosing further now the rain stopped I'm getting 13.6 volts now on the +B post of alternator but only 12.87 volts at battery engine running With engine and key off I get 12.87 volts at alternator + telling me fusible link is good between alternator and battery so still can't figure out why Im not getting 13.6 at my battery when engine is running?

[extech]

first.  need to say which battery we're talking about.  second are you using the same ground connection for all measurements