7 replies to this topic

[paulrockliffe]

I'm rewiring all my controls and have an LED illuminated starter button going in.  I want to wire the LED to the alternator warning circuit (retaining the original warning light as well) so that the switch illuminates when the ignition is turned on, but goes out when the engine is on.

 

I can't remember exactly how the alternator warning circuit is wired, is it balancing the current from the alternator with *something* so that the light only comes on with the alternator not working?  If so, can I avoid messing with resistors by keeping the original light as the low resistance of the LED shouldn't make any difference to the circuit?

 

Or what?

 

Cheers

[BaronVonchesto]

check out the wiring diagrams. I dont think the resistance will make much of a difference for the charge warning lamp, but the amount of current will likely overload the LED. It would be better to use a relay and a small LED driver circuit.

[slidehammer]

If the led in the starter button is already rated at 12v or has an internal resistor to allow for a 12v supply to be used them it should be fine, all I would do is tap into the wire that already goes to the charge light on the dash, running them in parallel. The charge light is controlled by the small spade terminal on the back of the alternator. The larger terminals are for the hi output charging system. Obviously you need to connect the positive and negative the right way around on the LED for it to illuminate.

[Icey]

The lamp lights when the alternator isn't self-sustaining - that's to say the field windings are being powered by the battery (through the lamp) rather than the alternators own output.

 

If you replace the lamp with an LED, you won't have enough current flow to 'excite' the windings, you will have to put a resistor in parallel which can flow enough current.

 

In short, no, there's no easy way to chop in an LED. You're best just leaving that circuit alone or looking for an alternator which has all of this taken car of for you (i.e. from a more modern car that has a tell-tale output not connected to the excitation circuit).

[paulrockliffe]

Yeah, I wondered about that, but I'd be leaving the existing light in place, so that would be OK wouldn't it?

[GaryDVO]

Yeah, I wondered about that, but I'd be leaving the existing light in place, so that would be OK wouldn't it?

 

I replaced all the lights on the dash to LED, I was advised as above to put the bulb back. All Good now

[paulrockliffe]

I accidentally found some cheap LED warning lights and made a new light panel for the dash and now don't need the bulb at all!

Any idea what resistor I should put in parallel?

[tiger99]

82 ohms but it must be rated at 2.5 watts, and will run hot. You could use a smaller version of the metal cased type used for ignition ballast and dim/dip, the smallest size is 2.5 watts but only when bolted down to some metal.