Alternator low volts, linked to warning light?

[Chimp871]

So first time out after engine rebuild and engine starts to loose power and refuse to rev over 2000 rpm. Get home and battery is at 11.4v.

Charged overnight to 12.4 volts and started engine but battery isn't increasing. Check alternator and shows 2volts.

Got it to my local specialist who tested alternator on his rig with all well.

He said if the warning light isn't working then the alternator won't get the signal to start cahrging battery.

Any truth in this?

[N7GTX]

Check/replace the 100 amp fuse in the fuse holder on the chassis near the starter motor. Just follow the large red wire to it. Also check the 80 amp fuse in a similar holder above the battery near the fuse box in the tangle of wires to be found there. If they have not been renewed recently then worth doing as they can crack and subsequently fail.

The red alternator warning light runs from the ignition switch to the alternator. When you switch on the ignition, a circuit is made by grounding through the alternator and the red lamp lights up. Once you start and the alternator comes on line i.e. starts to charge more than the battery voltage, then the light is extinguished by breaking the circuit.

Some pics in the link: http://tvr-parts.com/tvr-parts/by-model/chimaera?m...

Edited by N7GTX on Thursday 7th July 18:37

[Steve_D]

Yes the ignition light is important.

The voltage from the ignition circuit, via the lamp, stimulates the alternator to start charging.

If the ignition light is on before start and goes out after start and you know from the test that the alternator works then the 100amp fuse below the engine mount has to be the prime suspect.

If the 80amp fuse in the footwell was at fault then nothing electric in the car would work.

Steve

[Sardonicus]

If you have not also 12 volts at rear of alt big terminal then the chances are the main fuse as fractured or blown or a breach in the cable

Edited by Sardonicus on Thursday 7th July 20:41

[Chimp871]

Thanks for the help.

Just to close the thread.

The 100 Amp fuse was slightly fractured and replaced.

I had the alternator bench tested yesterday and they found the charging volts was 13.5 volts so had them change the rectifier to charge it at 14.5 volts - £30.

Car now shows 14.4 volts when charging and now the oil light has gone out but probably the battery light just wired incorrectly.

Car handles as it should. Just need to double check the tps volts and timing, then its off engine rebuild to dash varnish.