Hi
I am new to this forum and need some help.
I have an old car that I am working on, and the plan was to change the old status light (10W) with a LED.
The altornator has a built in switch that is about 700 ohm when the altornator is running and charging the battery.
If it stops charging, it will be 0 ohm and the bulb will light up.
The problem now is that the LED lights up constantly.
I tried to put a 75 ohm 3 watt resistor in parallell with the LED and it works, but it gets very hot and I dont think I can have it like that!

I am sure there is another way to do this and I need some help.



Thank you

 

Increase the parallel resistor to about a 700 ohm, 1/2W resistor (it will dissipate about 0.3W maximum).
Add a 7.5V Zener (1N755 or similar) in series with the LED.
Change the resistor in series with the LED and Zener to about 250 ohms (below).

The resistor drops the voltage to 1/2 the battery voltage when the alternator switch is open, and the Zener then keeps the LED from lighting.

 

Ok I will try that.
Thanks for a quick reply

 

What is the make & model if the old car?

 

1967 Chevrolet Camaro