Lights on - engine dies

[julians]

When the car is idling (fully warmed up), if I turn the lights onto main beam the revs drop and the engine dies. I know that switching lights on increases the load on the alternator, but I'm sure it never used to do this.

 

When driving along there is no effect, as you would expect.

 

Would a duff alternator cause this or are my lights drawing far too much current.

 

 

[Alex Wong1697456877]

More likely the lights are creating a short somewhere. Check the wiring to the ignition light. I once wired something to this thinking it was an earth, which it is, but only when the engine isn't running!

[John E]

Is it possible to run the engine without the alternator thereby eliminating it as a cause of the problem. Otherwise its going to be trial and error in finding a short.

[Graham Sewell]

If you remove the 'fan belt' then the alternator will not be driven - but this mode cannot be run for long without overheating.

 

Also, if the car is governed by an ECU, if the battery voltage drops too low because of loading, the engine would die.

 

 

[John E]

I agree but it would only take one try out of the lights to know if it was the alternator that was playing up. I wasnt sure if on these modern engines it was possible to do the simple elimination test. Having said that under normal use if the fanbelt goes pop then it should not be a total catastrophe.