Some quick math for estimating: typical incandescent bulb: 21w = 1.75A. Typical LED bulb 4w = 0.33A. That works out to 6.85 and 36 ohms

To make 36 ohms "look like" 6.85 ohms you need an 8.45ohm parallel resistance.

More than likely you can get by with half the initial current so rather than .875a I'll use 1a for a less wasteful solution.

1A takes 12ohm @12v. To achieve 12 ohm you put 18ohms in parallel with LED. That will put 8w on the resistor and be quite warm you need to assemble so it touches nothing and floats in space on the wire leads in open space so it cools.

8.5 ohm will be 18w very hot and hard to find

I would try a 15ohm 10w resistor that will get you over an amp and likely work. You can put two in parallel to get 5ohm 20w if needed.

At least 80% chance that 15 ohm will work. Try one as high as 20-35 ohm the higher that works the better. Less waste on heat.

Volt / res = amp. Amp x volt = power

Do The math to make sure power not higher than rated. The resistor will cook itself and can cause a fire. I use an app resistor calc to confirm values always.

-awr


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2011 E70 • N55 (me)
2012 E70 • N63 (wife)