Fast flashing indicators - what resistor do I need?

Ok I just fitted my (non-LED) indicators that have sat around for ages - and they flash too quickly (approx twice as quick). The bulbs in them (all 4) are 12V, 8W, and I understand the standard bulbs are 12V 21W. I've searched back through threads but I'm still not sure (and I want to be!) what resistor I need...can someone help?

Also if possible I would only like to put them on the rear ones (just easier than also altering the fronts) - so if that is possible can you also let me know what resistor I need if I am just going to use 2!

quick replies appreciated as I'll then be dashing off to maplin's before it closes in 2 hours....!

Don't 21W bulbs fit into your new holders? I had the same problem with fitting BUELL OEM indicators. I solved it by trashing the plastic orange inserts and buying 21W orange coloured bulbs. Very nice ad the flashing is now normal. You loose some brightnes when using 8W bulbs.

i wouldn't mind fitting 21W bulbs but i'm not sure where is a good place that will have a comprehensive range of bulbs - i looked in halfords and they have barely anything! the original bulbs in my indicaotrs are big old things...these are little bulbs, about 2.5cm high and a little over 1cm wide - that's for the whole thing, base included.

not sure where you're based - but if in london, do you know infinity motorcycles in clapham? i could pop down there as easily as i could pop to maplin's...

ok i should add - when i looked at the thread preview when writing the post, i couldn't see where you were. now i can

Originally Posted by muffles

...bulbs are 12V, 8W, and I understand the standard bulbs are 12V 21W....

Resistors are used to resist (and therefore drop) voltage, not power (watts). P=VI, I=P/V therefore the old bulbs current draw is 8/12=0.6 Amp. The new ones are 21/12= 1.75Amp. As partial justification for this, my car has a 40Ah battery. It can offer 40Amps an hour, this doesn't mean that all of the car has to use this 40Amps just to be able to use 12v.

General rule of thumb, you feed too much voltage through a bulb, it blows. However, the bulb will draw as much power (watts) as it needs to (up to the max on offer). If there isn't enought power on offer, or the voltage is too low, the bulbs will be dim.

In this siutation, if you use a resistor, you drop voltage, and dim the bulbs. This would in fact slow the flashing, as the SV uses a basic relay to control the flashing. This basic relay RELIES on the rest of the circuit to dictate the flash rate.

Resistors may be used if you fit an LED indicator setup. This is because LEDs use less voltage than standard bulbs, so the resistor drops the voltage.

A more advanced relay wouldn't care what voltage/power the rest of the circuit was using, and would give a constant flash rate. However, this will also stop you having an obvious clue as to if a bulb is blown.

In short, I recommend you buy a new indicator relay to solve the issues, and make sure it's the right type!

thanks - i phoned infinity and bought new bulbs instead 23W! cost me £13 for 4 though!

Well explained Baph. I'm a techie as I'm a radar technician but avoided the explainin, as well I am not good at it. But all you've said is true, I confirm. I'm happy that Muffles fond the bulbs he needed. are they small items Muffles? I opted to fit the old big bulbs instead but if you've found the little items for 23W all the better!

yup they are small items i think they are fairly easily available if you go to a motorcycle store, i think (either that or i was lucky!). they're just expensive, for bulbs! and they work perfectly now