Intermittent instrument lights

[bogart]

Long tale so I will start at the beginning.
Ignition off battery voltage is about 12.6
Turn on headlights etc drops to about 12.4
Ignition on lights off battery voltage is about 11.9
Start car, voltage about 11.9 with emission and abs lights permanently on.
Drive car for no more than a mile till warmed up come to rest ignition still on, emission and abs lights still lit.
Switch of engine and then restart emission and abs lights now out but SRS light lit.
Battery voltage is about 12.7
Rev engine until just under 2000rpm when SRS light goes out and battery voltage then jumps to about 13.8
Alternator belt was a bit slack so tightened but same faults persist.
Can see how voltage and SRS light are connected but confused by battery voltage/alternator output.
I always thought an alternator output varied with speed up to a certain point where it is limited. Here I have at say 1900 rpm an output of 12.7 then only a few hundred rpm more it goes immediately to 13.8

Sorry to be so long winded.

Regards

[Andy_Gibson]

Well if the alternator belt is correctly tensioned i'd say
the voltage regulator on the back of the alternator is knackerd then.

As soon as you start the engine and without revving the engine i'd expect to see atleast 13.2V and once the revs are taken over 2000rpm 14.2v.

What voltage do you get if you take the engine over 2000rpm with the car electrics loaded up ? (switch on the headlights,front fog lights, interior heater blower and heated rear window all on together to test this)