by David Zatz, Ph.D., allpar.com
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. That was Rick Ehrenberg's basic conclusion in Mopar Action, and also lighting expert Dan Stern's comment to us after he read the Allpar review. We concluded that the ideal would be somewhat brighter conventional bulbs and an LED-based third brake light; Dan also came to this conclusion, and we soon received a package containing, among other things, a Hella LED-based third brake light, and brighter bulbs for the brake lights and side-markers.
Installing the third brake light took far less time than we thought; despite our mechanical ineptitude, less than hour. We didn't even break anything. Tools required were a #2 Phillips screwdriver, a 7/16" wrench (yes, for unknown reasons they deviated from both 1/2" and their beloved 3/8" inch), and a pliers which we used to squeeze together the connectors. It would have been even easier, but we have combination brake lights and turn signals, which means that we had to tap into the brake switch and run a line all the way back to the rear of the car to having something that would only go on when we hit the brakes.
Our guide is for a 1974 Valiant but should be similar for most cars that run on 12 volts and have combination brake lights and turn signals. Dan Stern also recommended that we go even further, and move the turn signal operation to the reverse lights - so we'd have combined turn signals and reverse lights - which would allow us to use amber bulbs for the turn signals (and, obviously, for the reverse lights, so this is a modification that could run a person afoul of the local law.) We didn't do this, but we will try it out in the future. Dan noted that research shows that combination brake lights/turn signals are not as effective as "pure" brake lights; he also pointed to research that shows amber turn signals to be more effective than red ones. There's no particular reason to do both changes at once, though.
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. We actually used half of a heavy-duty outdoor speaker wire, mainly because we had it and it was a good heavy copper wire), then closing the second "tube" of the shell over the existing brake wire. We recommend you get a couple of extras at the hardware store before starting. Better yet, look into the Posi-Tap, which works far better.
There were actually 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 "hot" when the brakes were on. In our case, this was the outer wire. Also, while we ran a single wire, you could run two wires, one for ground, if there's no good grounds in the trunk; or you could run six wires, and have some extra wires in case you want to add rear speakers.
It is important to route the wires well, preferably better than the factory did. The kind of wiring I did when I was a kid was sloppy and quick, and often failed; fortunately I was just wiring speakers. When you deal with brakes, you take time to do it right. (Again, Posi-Tap and associated products may make a huge difference in long-term reliability.)
After carefully routing the wire on the underside of the dashboard so it would be away from moving parts and would not fall down, I unscrewed the screws holding on the thresholds by the doors on the driver's side. Then I removed the plastic front side trim panel (held on by a single screw), carefully keeping its orientation the same as the carelessly fitted insulation panel, badly installed by the factory, underneath it. Underneath that front side trim panel was the start of the wiring harness that led through the cabin back to the trunk; it was held in place by bendable plastic tabs, which I opened slightly and used to run the new wire. From the plastic panel the harness and my new wire ran through a deep channel underneath the first inch of carpet, which I wish I had taken the time to discover back in 1981 when I first installed a stereo in a Valiant.
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.
There are two reasons for removing the back cushion, the first of which is to make it easier to get the new brake wire into the trunk - you don't really need to move the seat back to do this, but it makes it slightly easier - but the second is to get the wire from the third brake light itself into the trunk. The alternative is to drill a very small hole into the package shelf, which will look neater but will let a little noise into the car, and also leaves a small hole in the package shelf. If you drill the hole, you can leave the rear seat cushion right where it is.
Once inside the trunk, it's easy enough to route the wire from the brakes. In my case, 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 very generous length of wire - to meet the brake wire. I pulled apart the Hella cable and took the ground part out to find a good ground (I ended up wrapping it around the inside of the gas cap retainer, a screw with a nice sharp end and no paint, and securing it with a small nut), and used a gizmo designed just for this purpose to tie up the power end to the wire from the brake switch. Everything is shipshape 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. Everything looked fine. The third brake light activates just an instant before the regular lights; it is fairly directional, so it is definitely brightest to people right behind it, but it is also quite bright from just about any reasonable angle. On the whole, I think this is the ideal solution for the problem of having sensibly bright brake lights in an age where people like to be blinded by the lights.
If you want one of these lights, Allpar suggests contacting Dan Stern, who can make sure you pick the right one (among other things, they come in a number of different forms for windows with different slopes. Dan picked ours and it was perfect.) He can probably also provide other helpful tips on lighting and wiring. It sure beats going to AutoZone, Pep Boys, or whomever, and blowing a bundle on junk.
Next: amber turn signals on a 1974 Valiant...without new lenses.
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