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Auto electrician needed!

  BMW 320d Sport

Not the right forum, I know, but I couldnt decide where to put it! Basically I need some advice on correct bulbs and power ratings to use in headlamps and stuff, plus mods to my lamps as well.

Im changing over my headlamps to Morette twins and you lose the indicators from the main unit - they supply some massive great orange things that youre supposed to cut into the bumper and use instead of the factory indicators, but they are enormous, like something off an Austin Allegro or something. So obviously Im not using them, especially seeing as even if I put them behind the mesh of my lower bumper, theyre so bright and huge you can see them even when theyre not flashing!

So the plan is this: I want to put the indicator bulbs into the actual lamp units, like the new Golfs have, so its all nice and tidy. Ill drill a hole through the reflector surface and use a grommet to insert the bulb holder into the lamp. The problem is that the normal 21 watt indicator bulbs are far too bulbous to go into the lamps, the only size that will look and fit right is the small bayonet fitting side repeater bulbs, 4 or 5 watt. And AFAIK if I put a 4W side repeater bulb in (or an LED equivalent) my indicators will flash double time because the wrong rating of bulb is in the circuit (Leigh has this problem with his)

Now Ive thought of every possible way of doing it and all I can think of is this - Im going to use the small 4 watt bayonet bulbs, probably a silvered one that shines amber, but what do I need to do to get the circuit to power them properly and not flash at double speed? My electrical theory has all been forgotten, do I need a resistor in series or parallel to give it the right load or something?

If the nominal voltage is 12v and the power is supposed to be 21w then current draw must be 1.75A (P/V)... for a 4w bulb it would be 0.33A. Therefore if R=V/I then the resistance of the 21w bulb must be 12/1.75 = 6.8 ohms. Or for the smaller bulb 12/0.33 = 36 ohms. So will putting a 30 ohm resistor in series with the bulb roughly sort it out and give the correct load in the circuit?

Thats what I was thinking about doing with my quads when I fit them (the indicator thing).

Ive got some motorbike indicator bulbs in orange, and I was thinking of putting them in where the side light bulb would go and move the side lights to some where in the front bumper.

Youre right about the indicators that Morrette send though, Sh*te.
  Clio 1.6 16V

The circuit should be calculated with a voltage of 13.8V as this is normally what your alternator regulates at when running. A 21W bulb will draw 1.52A. A 4W bulb will draw 0.29A. Therefore you require a resistor to draw 1.52A - 0.29A = 1.23A. The resistance required in parallel is 13.8/1.23 = 11.2 Ohms. A resistor capable of dissipating 13.8 * 1.23 = 16.97W is required. This will have to be a metal cased wire-wound resistor mounted on a metallic heatsink (eg. bodywork).

Hope Ive got that right ...had a few glasses of wine!

  BMW 320d Sport

Dave - so the motor~~~~ indicator bulbs are the same shape and size as car sidelights (ie small bayonet fitting)???

Cheers Neil!
  2012 WRX Waggon

you could use a variable resistor to set your own flash rate!!

silverfusion do those silvered bayonet lamps by the way - we might have a club discount with them soon!!
  BMW 320d Sport

Ben - theres not a lot that Im not sorting out once and for all on this Clio. Its gonna be exactly how I want it.

Yep the indicator bulbs from motor bike indicators are sbc so they will fit.

Not quite sure if when youve got the headlights on wether enough light will be given off by the indicators. On all the new cars with indicators built into the headlights theyre set away from the headlight beam.

Might be a bit tricky when it comes to MOT time. :confused: