Alternator warning light

[Theo]

I've recently installed a dash 2 to my Nissan powered BMW E30 and one of the few teething problems I'm experiencing relates to the alternator light of all things.

The original alternator no charge light works by a voltage difference between a separate alternator terminal & 12v at the battery. When the alternator terminal is at 12v the light goes out.
I have connected the lead from the separate alternator terminal to the relevant wire on the dash 2 but the light does not go out.

Can anyone suggest what I need to fix this? I've included a wiring diagram below.



Thanks

[pault]

I'm not exactly sure of the wiring changes you made. Did you just connect the alternator to the Dash 2, is the alternator still connected to the light and is the light still connected through the fuse to a 12V source?

Paul

[Theo]

Hi Paul - at present I simply have the w/r wire connected to the dash 2, I only looked into the circuitry after it didn't work properly. There is no light or fused link to 12v.

[pault]

So what you need is a pullup resistor on the W/R wire. It is my understanding that the alternator needs current flowing into the L terminal to get going. You will want a resistor equivalent to the the lamp resistance. Be careful of the wattage rating of the resistor. The 7.5A fuse (#25) implies a big current, unless it is shared with other circuits.

For reference:
http://alternatorparts.com/understandin ... nators.htm

Paul

[Theo]

Thanks very much for that, will try it out this weekend.

Theo

[Peter Carroll/Toronto]

To use the alternator LED on the DASH you have two options...

2 wire alternator: Battery plus small field wire. In an OEM config, the field wire goes to a bulb. The voltage across the bulb lights the bulb. When the field is energized, the bulb is at battery voltage and it goes out. The LED can not do this. You need to either provide a bulb, or I prefer to use a 5 ohm(ish) resistor (get a big one as it will get hot - 25W(ish)?). Connect the LED to the field side of the resistor and the other to battery voltage.

3 wire alternator: Battery plus two small wires. One is the field wire and the other is the bulb. In this case the resistor is built into the alternator so just connect the LED to the bulb wire.

[Support]

There is a 100 ohm resistor in parallel with the bulb inside the DASH2 to provide the required current to energise the field. This is fine for most alternators but some do require more current. If this is the case then you will need to connect a resistor as described between the 12v supply and the field wire.

Martin