by David Zatz
Our conclusion after trying out LED brake-light replacement bulbs was that they were generally useless; there are quite good replacement modules designed for specific cars, but the bulbs are less than ideal. Rick Ehrenberg of Mopar Action and lighting expert Dan Stern came to the same conclusion. We concluded that the ideal would be somewhat brighter conventional bulbs and an LED-based third brake light; and Dan soon sent over a Hella LED-based third brake light, with (unrelated) brighter bulbs for the brake lights and side-markers.
Installing the third brake light took very, very little time — despite my mechanical ineptitude, less than hour. I needed a #2 Phillips screwdriver, a 7/16” wrench (yes, they deviated from both 1/2” and 3/8”), and a pliers to squeeze the connectors. If we did not have combination brake lights and turn signals, if would have been easier; but we had to tap into the brake switch and run a line all the way back to the rear of the car so the turn signals wouldn’t interfere with the brake lights.
We have a 1974 Valiant; the routine is similar for most 12-volt cars. Dan Stern recommended that we also move the turn signal operation to the reverse lights, so we could use amber bulbs for the turn signals (and, obviously, for the reverse lights, which probably makes this modification illegal in many states.) This remains, sadly, a program for the future, though brake light/turn signal combo units are not as effective as “pure” brake lights, and amber turn signals are more effective than red ones (Dan sent research to prove his claims).
First, we ran a wire from the front of the car to the back, starting at the brake switch. We tapped into the existing wire using a finicky wiretap supplied by Hella; this worked by threading the new wire through the center (just a single wire, not a pair of them formed together), then closing the second tube of the shell over the existing brake wire. Get a couple of extras at the hardware store before starting. Better yet, look into the Posi-Tap, which works better. (For the wire itself, I used half of an outdoor speaker wire because I had it, but it’s best to use a proper auto wire.)
There were two wires leading away from the brake switch, and we used a voltmeter to figure out which one supplied current all the time, and which was only used when the brakes were on — in our case, the white wire. While we ran a single wire, you could run two wires, one for ground, just as easily.
Wire routing is important. When you deal with brakes, you take time to do it right. It’s very little time, as it happens.
After carefully routing the wire on the underside of the dashboard so it would be away from moving parts and would not fall, I unscrewed the screws of the chrome thresholds by the doors. Then I removed the plastic front side “kick” trim panel (held on by a single screw), keeping its orientation the same as the carelessly fitted insulation panel. That revealed the start of the wiring harness that led to the trunk, held in place by bendable plastic tabs, which I opened slightly for the new wire. From there, the harness and my new wire ran through a deep channel underneath the first inch of carpet.
Once the wire reached the rear, it was time to take out the back seat, a moderately awkward task. In this Valiant, the lower cushion comes out first, but pushing against a catch on the bottom - back and up - on one side and then on the other, making sure the first side doesn’t pop back in again first. It’s much easier after the first time. Take the lower cushion out, vacuum or clean underneath, rescue the build sheet, and look for two bolts holding on the back cushion.
You have to take off the back cushion both to ease getting the brake wire into the trunk, and to get the wire from the third brake light into the trunk.
The alternative is to drill a hole into the package shelf, which will look neater but will let a little noise into the car, and, of course, leaves a hole in the package shelf. If you drill the hole, you can leave the rear seat cushion right where it is.
I expect to try out the amber-turn-signals trick, so I ran the brake wire all the way down to the far end of the trunk, then ran the third brake light (Hella provides a generous length of wire) to meet the brake wire. The ground came from wrapping the wire around the inside of the gas cap retainer, a screw with a sharp end and no paint, and securing it with a small nut). Then I tied the power end to the wire from the brake switch. Everything is firmly held into place and routed where it can’t get into trouble.
After an initial test I took the car for a spirited ride, took turns sharply and drove over bumps, and checked again. The third brake light activates just an instant before the regular lights; it is brightest to people right behind it, but it is also visible from just about any angle. This both solves the problem of people expecting to see a third brake light and not observing the normal lights, and the fact that 1920s-1980s brake lights are far, far dimmer than 2000s lights.
Dan Stern can make sure you pick the right kit (they come in a number of different forms for windows with different slopes) and provide other helpful tips on lighting and wiring. It sure beats going to AutoZone, Pep Boys, or whomever, and blowing a bundle on junk.
Update: This was first posted in 2007. We did a heavy edit in 2016, but one thing hasn’t changed: the wiring is still perfectly in place and the third brake light works perfectly. In a region where drivers are notably poor, it has likely avoided at least one collision.
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