Has anyone successfully changed the battery light to an led? To mimic an incandescent bulb, would a resistor need to be used?
I plan to recreate the cluster backlit, so any help with this specific indicator would be appreciated.
Location: FL
Posts: 947
My VIN: Early
Has anyone successfully changed the battery light to an led? To mimic an incandescent bulb, would a resistor need to be used?
I plan to recreate the cluster backlit, so any help with this specific indicator would be appreciated.
Early 81 5spd conversion- DMCH Ground Effects, Double Din, Custom Instrument Cluster, QA1 Suspension, 3.0 PRV with MS3
Posts: 46
My VIN: 5564
In theory it can be done, However you would need to place a resistor in the circuit I would think to mimic the current output of the incandecant since the led bulb draws less current. Also voltage may be a problem too, an LED diode only passes around 3 volts if I'm correct. You may need to test the voltage and current out put of the Brown/Yellow wire to the alternator, switch it with and led and place a resistor to mimic the circuit.
Location: Leonardtown, MD
Posts: 9,005
My VIN: 03572
I would guess you need a resistor of 200 ohms to drive about 50 ma. into the field to get the alternator started. Then you need to measure how much voltage you get over that resistor to see if a standard 12 volt LED bulb would work.
A better way is to use the resistor driving the field and make up another circuit that turns on the LED when battery voltage is below 13 volts. That way you can always get a bright LED light when the alternator belt breaks.
Location: SoCal
Posts: 146
You don't need to have the resistor in series. Just use a standard 12V LED bulb, same as you'd use on the rest of the dash, and put a 220 ohm, 5 watt resistor in parallel. You'll have to splice it into the wiring or solder it somewhere, I'm not actually sure what the instrument cluster looks like back there.Originally Posted by Bitsyncmaster
(5 watts is overkill, but it would be dissipating about 600mW, and I imagine space is cramped back there and it would heat up, so better safe than sorry.)
Posts: 605
it was designed for a bulb, it works with a bulb, it' only needed a few seconds when starting the
car - why mess with it ?
Location: Leonardtown, MD
Posts: 9,005
My VIN: 03572
That is why I have not designed a change to use and LED. The bulb will never burn out from use since it's only on seconds at a time. Only good reason is if you want something brighter than the standard bulb to get your attention.
Posts: 4,764
My VIN: Banged your VIN'S mom
Bingo
Location: Northern NJ
Posts: 8,579
My VIN: 10757 1st place Concourse 1998
If a red warning light in your dash doesn't get your attention, making it brighter probably won't help. The bulbs do occasionally burn out but that is no reason to try to convert it to an LED.
David Teitelbaum
Posts: 520
what's gonna happen if you put a led bulb, alternator failure or just not working? I have an alternator which is advertized to be compatible with a led bulb, but I never tried the swap so far.
Let us reply to ambition that it is she herself that gives us a taste for solitude.
Location: Leonardtown, MD
Posts: 9,005
My VIN: 03572
Alternators have needed some current feeding them to get them started. The bulb is what drives that current into the alternator. If you use an LED the current that it would drive is much lower. It may work or may not. Also LEDs are more sensitive to damage with voltage spikes.
There is really no need for alternators to need that current drive with the use of micros now in new designs. That is if everyone would decide to implement that change.
Back when we used generators, you had to polarize the generator to create a little magnetism in the field. It would hold enough magnetism to self start after that one power pulse.
Last edited by Bitsyncmaster; 06-28-2016 at 05:35 PM.
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