Voltmeter always reads just over 13 volts when I start the car, then drops to 12.5 or so.
What can I do to see if the alternator is working/charging properly before I consider anything else?
Thanks

 

A digital voltage reader in the cigar lighter socket should give you an accurate reading, eg:

 

Paddyx350,

Measure the voltage with the engine running, directly at the battery terminals, and also at the bulkhead +ve & -ve terminals. Do not rely on a reading from the voltmeter. It's very often reading low.

Paul

 

So put a multi meter on the battery.
When its not running 12.8V, when it's running 14.04V.
Left it running for 10 mins and the voltage had dropped to from 14.04V to 13.93V
So is everything as it should be?

 

100% OK

 

Your charging circuit seems fine, but, as expected, your voltmeter is reading low.

A clean up of the cluster connections and possibly running a separate earth can improve things.

Paul