If you can get 13.8 volts with everything on then you have the most effecient alternator in the world, never in a million years will this happen at idle.
The test should really be done around 2000rpm.
The "entiser" wire does not exist, what they are trying to get at is on battery excited alternators the LIVE comes through the bulb to intiate charging once engine running/alternator rotating, that said rev it around 3500-4000 and it will still kick in everytime.
They can as said fail to charge even if the light goes out, they can also charge even if the light stays on, depending on where the fault is.
The FIRST thing you need to do to get a accurate test is charge the battery fully or the test is meaningless, then test lights etc off at 2000rpm, then again with everything on at 2000rpm.
It should be anywhere around or above 12.8-13.8 with things off, with things on anywhere above 12.6 is acceptable, though some charge at 15 volts.
If you have a lot of stereo gear you might consider a uprated one, alternators will typically put out on a CONTINUOUS basis around 1/3 -1/2 of the rated current which is a max peak which only needs to be there for a second.
Another alternative is to change wiring from start to delta, as this will give around 60% more charge at the same speed lower down, but no more in total.
tabetha