Although amps were mentioned in the first post, I think that we are talking about a 16 volt charging rate. We don't know that amp charging or discharging rate.

I am not familiar with where that voltmeter pulls its reference, but I think that the older alternators had ground straps that are prone to failure. I would run the car up on ramps and get underneath and make sure the alternator is well grounded, and clean all the 12 volt connections on the back of the alternator while I was down there with the belly pan off.

A battery that will not accept a charge or a poor electrical connection or ground can cause the problems you describe. You can tell more about what is going on with a cheap $10 voltmeter. Trying the lights and horn will tell you if your battery is completely discharged, but not much else. Your battery should measure 12.6 volts when the car is turned off. This should drop to 10-11 volts while it is cranking the engine. When the engine starts, it should charge at (shoot, I have already forgotten) somewhere in the high 13s or very low 14s at fast idle, measured at the battery posts

As noted in another post, Volvo starters rarely fail, though I had to replace mine a few weeks ago.

The starter is the black electric motor bolted to the engine, down low, driver side. There is a solenoid (electromagnetic switch) which is about the size and shape of a 6 oz can, attached to the top of it. The electrical connections are on the forward end of that solenoid. If you try to short across the connections to test bypass the ignition switch, it will spark and may ruin your screwdriver. Keep your face away from it. Be careful not to short those positive terminals to any other metal part or you may weld your screwdriver to the engine permanantly, and cause a lot of damage.