Engine Dies When Headlamps Turned On

[anonymous-user]

Has this happened to anyone?
What should I be looking at?

[Zeb74]

I had the same thing once in the past, I have a circuit breaker under the dash on the passenger side and my wife accidently cut it with her knee. The car was already running and seemed fine, the electricity generated my the alternator was sufficient. However, when I was high in the revs, or I was putting the light on, the engine was cutting badly.
If your battery were totally dead, you would have difficulties to crack the engine. But I would check the connection between the alternator and the battery.

[guards red]

If it's got an idle control valve it'll be that I suspect.

[sunbeam alpine]

When I had this (not on a TVR) it was the battery. Can you try a battery from another car temporarily?

[blaze_away]

sunbeam alpine said:

When I had this (not on a TVR) it was the battery. Can you try a battery from another car temporarily?

Good advice, could be the battery not being charged by the alternator so everything is running off whats in the battery. When lights go "On" volts drop and coil falls over generating no spark and a low volts to everything else, ie fuel pump ecu etc

So try jumping another battery on tp it and check volts coming from alternator and at battery terminals. Engine running it shoul be at 14+ v at both.

Edited by blaze_away on Thursday 21st September 09:41

[Polly Grigora]

There are at least 4 possibilities

Alternator load is dropping the engine revs and not being compensated for

Battery voltage is dropping too low

Ignition system supply is breaking down or dropping too low

There is an ignition system relay dropping out due to its earth or supply breaking down

Flick of a coin jobby innit

First things first though, check battery voltage when lights are switched on, then ignition coil supply and then........

[anonymous-user]

Thanks for all the replies
It has been very helpful
I guess I can rule out head lamp switch?

[anonymous-user]

I forgot to mention the engine dies when just instrument light turned on!

Any ideas?

[Rocky-TVR]

If it were to be me, I’d take some voltage readings at the power source to the ignition box (if you have one), and at the coil positive. I’d first take them with the ignition on (not running), and then with the car idling.

That will tell you if something is drawing down the ignition source voltage when instrumentation lights, and main lights come on.

Seems like you may have some kind of sneak circuit to ground through your lighting system.

Rocky