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Electrical guides and mods

Hella 451 DRL Repair

The 5 per side Hella daytime running lights on the 451 where surprisingly poor quality and failed regularly.

Modification Details




Over Priced Hella DRLs

If you have a fortwo 451 with the single 5 a side Hella daytime running lights, at some point, some will fail.



Why Do They Fail?

Hella charge a lot of money for their lights, so why are they shit? Very simple, cost cutting and money saving.

The body is made from aluminium and much like the Brabus alloys, they aren't zinc primered before painting.
This means that over a length of time, aluminium oxide (rust) forms on the surface of the body between the
aluminium body and the paint. The oxide layer is fluffy and is a poor base for the paint.

It doesn't take long for the paint to delaminate and the oxide layer creates a direct route for any water
to wick directly into the light housing. Once in there, the water and the electricity causes corrosion of
the LED connections and the copper tracks on the printed circuit board.



I got sent a few faulty ones by Dreamliner CDI. This was the worst one. Everything had corroded.



Repairing The DRL Unit

You have to lever the plastic lens out. Heating the unit up can help soften the glue.



It'll flip out fairly easily.



Flip the unit over...



...and heat it up with a hot air gun or solder rework gun.



This will break down the resin used to waterproof the screws. Gouge the resin out to access the screws.



Remove these screws and you'll then be able to remove the black front cover.



Behind that you'll see the PCB. Lever it out of the housing. This can take some force.



It doesn't matter if you destroy the PCB taking it out as we are replacing it.



Look in the housing and you'll see 2 raised nubs. These need to be gone. I cut them back
with a pair of side cutters but you can file or grind them down, which ever way you prefer.



It's a good idea to clean the housing up as much as possible. Certainly better than I have here.
Spraying the housing sides with zinc primer will stop aluminium oxide from forming again.



The LEDs used in these units are Osram LUW W5AM witha 6500K colour temperature.



You'll not get exact replacements for the original PCB so we'll use a star emitter base and solder the LED to it.



You can solder using a standard soldering iron but in this example, I'm using a hot air rework gun and solder paste.



You just squirt a little bit of paste on the pads.



To aid heat dissipation, heat transfer compound should be used between the LED and PCB. 



Just squirt a little blob in the centre.



Squidge the LED down...



...and then heat around the outside evenly with the hot air rework gun (or solder the LED legs).



Once the solder has melted, it's ready for wires.



The star emitter base is + down one side and - down the other. Solder on your wires.

Your existing wires may be very corroded so you may need to replace them totally.



Squirt some heat transfer compound into the housing...



...and push the newly constructed LED into the base remembering to line up the screw holes.



Place the black cover over the LED, again remembering to line up the screw holes on the back of the cover.



Replace the screws in the back. This black cover pulls the PCB and holds it in place.



Glue the lens back onto the housing, ideally with polyurethane adhesive.



You now need to reseal the rest of the unit. The screw heads need to be re-covered. Polyurethane adhesive is best.
Then spray the unit with paint or conformal coating to stop any further corrosion.

Alternative LEDs

You can forego the creation of your own LEDs if you don't mind using different LEDs.
Below is a common luxeon star emitter. They are available in 1 watt, 3 watts and 5 watts.

I would recommend 3 watt replacements.


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