Replacement dashboard instrument lights

[Pete Lewis]

here you go its one of them Must Haves you must do your homework first or its becomes a  lust you must not have 

pete

[Pete Lewis]

can you get a vaccination against Must have's    ha !

Pete

[Badwolf]

So, if the bulb has blown or not fitted correctly the car might not start?

[Pete Lewis]

wont stop it starting but may have an adverse effect on the charging /cut in 

pete

[GrahamB]

My son was having a problem with the instruments on his Focus so drove with one of the harness plugs disconnected.  Started as normal but came to a halt after a few tens of miles as the battery was completely flat.  The disconnected circuits included the ignition warning light so there was no current through the bulb to activate the alternator.  It may only require a very small current to activate the alternator so you may get away with a LED but there is no guarantee.

However, after studying the in-built regulator circuit, if the ignition light, be it a filament bulb or LED, goes out, then the alternator must be activated and generating at least 12 volts.

[GrahamB]

The previous post relates to an alternator.  If you still have a dynamo, these rely on residual magnetism in the coils to activate the charging system.  A relay within the regulator box then closes once the generated voltage exceeds the battery voltage and extinguishes the ignition warning light.  Therefore, with a dynamo system, the battery will still be charged whether it is a filament bulb, LED or even missing.

[PeteH]

Thanks Guys. I`d forgotton that. Early day ships H-V alternators had a separate Coil/Winding to supply the main field coils, bloody long time since I did all that theory.

If it comes on and the motor is running, you usually finish up having to get the "girl friend" to remove her tights!.😃

Pete