3rd tail light: Resistor size?

[Big Z]

Does somebody know the resistor size for the 3rd tail light, LED? '01 sport..I replaced the old one, and I broke the wire off the old resistor riiiiight off the end and couldn't get solder to hold. I then proceeded to break off some of the brittle resistor insulation as I cleverly removed the heat-shrink tubing with wire strippers, so now I'm not sure if I have the right color code remaining: Brown, gold, blue, white; brown on the line side. Looks like the only way to buy them is about a 50,000 pack for 5 bucks; I just wanna pick the right one outta the pack when they come in.

 

[Stic-o]

You could just replace the whole thing. I have like 3 spares ones in the garage

 

[J_C]

Can you determine based on its size, what wattage it is? Often the 50,000 resistors for $5 type packs have 1/4W capacity at most, if not only 1/8W capacity which if it's a single resistor feeding the whole light, may be too small a wattage. I'd bet the wattage on it is at least 1W and probably 2W. 2W resistors are usually about 4mm diameter in the middle (not the end caps).

Once you determine what value you need, you can buy just that value from an electronics supply house like Digikey.com for somewhere between a few pennies and a few dimes a piece (might have to buy 5 or 10 minimum but that usually totals under $2) and for something that small (under 8 oz. IIRC) they have fairly reasonable USPS shipping rates, under $3 the last time I checked but it's been years since I placed an order there which was that light weight.

Anyway if enough of the resistor end caps remain, you should be able to use a multimeter to measure resistance.

How is the light configured as far as # of LEDs in series or parallel? Big_Z if you don't know, perhaps someone else does. Given that info a good value of resistor might be arrived at mathematically.

I'll throw some numbers out there. I saw a picture that suggests there are 12 LEDs. IF they are red, their forward voltage is around 2.0V per LED. That means they couldn't all be in series, the sum voltage drop would be too high, so they would more likely be arranged as 2 parallel runs of 6 LEDs in series.

If that is correct, I'm supposing they might want up to 20mA drive current per parallel run, so with that in mind, the only resistor value that makes even a little sense based on the colors you reported is 96ohm, 1%, 2W. That could easily be wrong - I have made too many guesses in a row and advise that you measure with a multimeter or provide more info.

The other experimental way to go about it would be to have an array of resistors on hand, or a rheostat, then progressively, starting from a high resistance value like around 1000 ohms, progressively decrease the resistance while measuring current with a multimeter, and voltage drop across the resistor to find remaining voltage drop across the series of LEDs and calculate current per LED from that, not letting the resistance get low enough that more than 40mA current is flowing until you know what you're dealing with and not even that for more than a few seconds. 20mA would be a more conservative max level to stop at, with enough data to calculate what's going on.

It would be much easier to just measure the resistor with a multimeter if possible. If you don't have one, Harbor Freight sells them for $4 one week, free with coupon the next week, or about $5 on ebay.

 

[1998Exp]

As someone suggested, measure the value of what was there, if you can. Otherwise, your colors seem to read 19.6 Ohms, 1% tolerance.
I am not familiar with the brake lights on a 2001 Sport, and simply controlling the current with a series resistor borders on the ridiculous these days, but perhaps they didn't know any better twenty years ago. If that's indeed all there is to it, there should be something on the order of 6V (half the supply) across that resistor, which means that it will be dissipating about 2W. The Ohm value is not critical -- anything within 20% of the correct value should work. The power rating, however, is. If that indeed was a 2W resistor, it should look like a cylinder of about 1/4" diameter and about 1" long. If it's larger than that, it's probably 5W. You can buy those at just about any online electronic supply store (Digikey is one), and they may have a minimum quantity on the order of 10. The cost will probably be around $1, and it may cost another buck or two for mailing. I don't know where you found that grab-bag of 50,000 different values for $5. If it exists, these are probably junk, or perhaps a roll of small wattage (think 1/8 Watt or less) surface-mount type resistors, all the same value, used for machine assembly, but that roll will cost a lot more than $5.

Does somebody know the resistor size for the 3rd tail light, LED? '01 sport..I replaced the old one, and I broke the wire off the old resistor riiiiight off the end and couldn't get solder to hold. I then proceeded to break off some of the brittle resistor insulation as I cleverly removed the heat-shrink tubing with wire strippers, so now I'm not sure if I have the right color code remaining: Brown, gold, blue, white; brown on the line side. Looks like the only way to buy them is about a 50,000 pack for 5 bucks; I just wanna pick the right one outta the pack when they come in.

 

[J_C]

^ Avoiding current regulated switching circuits that involve a (electrolytic considering their penny pinching) capacitor is not all that ridiculous when you have the granularity of a series of 2Vf LEDs.

It's a different situation than ideal lab temperatures when in a vehicle outdoors, and good (design) control over sum forward voltage... for a light that isn't high current, and it works, given an alternator which isn't so much a finite source of power so conservation isn't an issue, the heat is quite manageable.

In other words, I wouldn't put an LED driver circuit in this. The resistor was the right design choice. It just increases points of failure with no important gains to use a dedicated active driver circuit in this application. The negatives outweigh the positives in this particular case. They often don't, but this time they do.

Plus, if it had been an active driver, we'd have seen a lot more failures by now instead of it being a relatively maintenance free part for the majority.

 

[Big Z]

It seems the physical dimensions point towards a 2 watt axial resistor with a color code of 9.6 but a metered 30 ohms.
L: 0.575"
W (center): 0.170"
W (belled end): 0.187"
Wire gauge: 20.
I think I'll pick up a 2 or 3 watt assortment and see if the lights run bright at 30 ohms and work down from there.