Do-It-Yourself Halogen Reversing Light

If you live somewhere that's dark and difficult to reverse out of at night, this light's for you. So many cars have got lousy reversing lights - sometimes apparently put there only for legal reasons - that it's a lucky dip what you hit and what you get past. But while you might want to upgrade the reversing lights, not too many people want the visual impact of a single large driving light mounted on the back of the car!

But this quartz halogen light is so small that you can tuck it under the rear bumper, out of sight to all who don't get down on their hands and knees. It's also cheap and easy to make.

The Parts

You'll only need a few parts to make the light. First up, the black thing is an ordinary towball cover. The light (with inbuilt reflector) is a 12V halogen downlight of the sort used in commercial and domestic lighting - they're available from everywhere that sells light bulbs. The other item is a small magnifying glass, which is used to make the beam more even and protect the bulb. (Alternatively, you can buy a bulb which comes with a clear glass cover built in.)

This particular towball cover came with an internal metal spring strip, but it's easily removed. A metal towball cover would be even better, but they're hard to source.

The 12V lights come in different wattages and beam shapes. A 20W unit is best - despite being less powerful than a 50W bulb, by the time the voltage drop of the larger current draw is taken into account, a 50W lamp can be no brighter than a 20W one! The 20W bulb also saves the reversing switch having to work too hard. Wider beam spreads are usually more useful than narrow ones - though it depends a bit on if you are going to use a proper lens.

We decided to use a convex lens (ie one like a magnifying glass) that had been salvaged from a slide projector. A small glass magnifier could also be used - or you could use nothing at all and select a halogen bulb with a 'lens' built in.

Building It

If the pins are cleaned-up with a file, the cable can be directly soldered to the lamp. Connectors are available for the bulbs, but they can double the cost of the project!

Place a knot on the cord (so it can't be pulled out) and then feed the cord through a hole drilled in the back of the cup.

A little experimentation with the bulb and the convex lens showed that a good, even spread of light was obtained if the front edges of the bulb reflector were right up against the lens. (Some other combinations might need the reflector spaced back a bit from the lens.) The cup was then stuffed with some acrylic quit wadding that was handy (any springy relatively non-inflammable substance could be used) so that when the lens was inserted, the bulb would be pushed up against it.

The lens - which was sized to be a push fit inside the plastic cup - was then glued into place and the light tested. If the lens is undersize, use black silicone sealant to glue it into place. (This also applies if you are using bulb that comes with a glass cover.)

Wiring of the light is easy - just find the pair of wires that run to the reversing lights and connect to those. The connections were made here with plastic crimp connectors. (The extra two are for the centre high mount brake light that was previously added.) Note that a 20W extra reversing light shouldn't cause any problems, but if the fuse for the reversing lights keeps on blowing, just upgrade its current rating a little.

The light could then be mounted under the bumper with a small bracket.

Heat! This light is not designed to be run for long periods! As a reversing light - where it's on for less than a minute at a time - it's fine, but if left on continuously, the plastic towball cover will melt! If you want to follow the same general approach but run the light continuously, source a metal towball cover and use a high temperature silicone adhesive to hold both the reflector and lens in place.

Too Dim? If you find that the new reversing light is much dimmer when installed than when you were testing it, it's probable that a voltage drop is occurring through the thin factory wiring. A normal automotive relay can be used to overcome this problem, installed as shown in this circuit diagram.

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