Old and new alternator not charging

[jeno]

Old alternator we're showing 11.5 volts at the alternator I assumed alternator was bad replaced with new one still shows 11.5 bolts on the new one . When I parked the motorhome last year everything was working great I took the house batteries out and brought them in the house and put them on a trickle charger after that a month or two later I had to move the motorhome so I started it up and moved it but noticed the alternator wasn't charging I wonder could I have done something when I left the cables for the house batteries on the metal tray ? But now when I put the new alternator in I had already put in the house batteries and have them hooked up any thoughts?

[DaveVA78Chieftain]

The B+ lead from the alternator goes to the large B post on the starter solenoid. However, there is a fusible link at the starter solenoid that will result in the alternator not working if it has blown.  With the engine off, make sure you have battery voltage at the alternator B+ terminal at all times (key ON or OFF).  No voltage means the fusible link has blown.  Also, the fusible link can start going bad due to heat and age (lots of current going through it) resulting in high resistance and screwing up the charging circuit.
On the small wire alternator plug,  the Pink/Black wire (from ignition switch) should have 12VDC on it with key ON, engine OFF.

If you have the DUAL-NORM-MOM switch on the dash, then Charging of the House battery is via the Dual battery solenoid however, the battery B+ lead from the starter solenoid and the B+ lead from the chassis battery should be connected to the same post on the dual battery solenoid.

You most likely have a 1989 rig on a 1988 chassis (check chevy chassis VIN to confirm).  Your a Life member so the the service manuals for that chassis are in the member area for free.  Power wiring diagram for the P30 Motorhome chassis (P32 model) is Section E, page 3

The small alternator plug connection is shown on Section E, page 17.

[jeno]

Ok this is stupid but I'm glad it was this easy. I think when I tighten the belt i didn't have it straight in the pulley and when I started it it slipped into the grooves and then the belt was loose and was putting out anything when I went back there to look at it I seen the loose belt I tightened it and suddenly 14.5 volts. Thanks guys for the help even though it was just my little stupid mistake....

[M & J]

No worries. It happens.