Adding a Third Brake Light

By Len Cannizzaro

Originally published in the Austin-Healey Magazine, January 1995


The rear lights of a Healey 100 will never be the grounds for a lawsuit against you for blinding the guy following behind—especially in the daytime. Thoughts about adding a third brake light, as is now required in all new cars, have been rattling around in the ol’ cranium for some time now. As with other additions to my Healey though, they would have to conform to certain criteria. However—don’t drill any holes in the body, and make it so the car can be returned to unaltered condition with minimum damage and effort.


The first task was to finds a suitable light for the job. I finally zeroed in on part #12-7650A in the JC Whitney catalog. Price: $9.95. This light has several advantages: it is designed for exterior use and is weather resistant. It has a slightly contoured base similar to the curvature of a Healey trunk. It measures 2 1/4” high by 7 1/2” wide by 3 1/8” deep, and has two replaceable bulbs each wired separately with its own color-coded lead and a common ground. This meant that not only could I use the light to warn someone behind me that I was braking, but also I could also use the lamp to supplement the Healey's directional signals. If for some reason you can’t get this lamp through JC Whitney, contact the manufacturer, Sierra Products, Livermore CA, for the name of another dealer.


To mount the lamp, I removed the sticky rubber pad supplied to mount the light, and bought some strips of universal rubber pad at an automotive flea market. The strips of padding are flat on one side with a round beaded edge on the other, and cost me $1 a foot. Lay out the pad on the three-sided light base (more on this three-sided business later), cut out pie-shaped wedges at the two radiused comers so the pad will fit around smoothly and use contact cement to glue the pad to the light.


To modify the light so it could he mounted without drilling any holes in the body, I used magnets mounted to pieces of wood in the two cavities under the light. One of the cavities has straight sides and is kind of triangular shaped. Start with a piece of wood about 1” x 1” x 7”, figure the angles and cut. You will need access to a table saw to make these cuts accurately. When this piece lies in the cavity properly, make the final height cut so that the surface of the wood will be level with the plastic base of the light, not the rubber pad.

For tilling the larger cavity I used two pieces of wood with a space in the middle for routing the wires through the back of the light. Start with two pieces of wood about 1 1/4” x 1 1/4” x 2 1/4”each. One side of this cavity is straight while the other is curved. I put a sanding disc in my hand drill, clamped it in a vice and made the curved side by sanding a little at a time — making many trial fits — until the pieces lay properly in the cavity. As before, make the final height cut so that the surface of the wood is even with the plastic base of the light. Finally, epoxy glue the three pieces of wood into the cavities, leaving a gap of about 1 1/2” in the center between the two pieces with the curved sides.


The 3/4” x 1” x 1/8” ceramic magnets I used came from Radio Shack (catalog number 64-1879). They come five to a package and cost $1.69. Buy two packages. The next step is to use a wood chisel to cut recesses in the three wood pieces that you glued into the light so the magnets can be installed. Here, again, a little cut and trial process is needed. You want to chisel out the depth of the recesses so that, when installed, the surfaces of the magnets facing the trunk lid are even with the faces of the rubber base pad.


The magnets come with a hole pre-drilled in the middle. Use small flat head wood screws to fasten the magnets to the wood pieces. Install two magnets— side by side—in each of the small pieces of wood and three in the long single piece. Finally, I covered the magnet faces with some clear Teflon tape so as not to scratch the paint on the trunk lid. I think pieces of black electrical tape would work as well. At this point you have rubber pad on only three sides of the mounting base. Now that you have installed the long piece of wood on the edge at the base of the lens, you have a surface on which to contact glue the rubber pad on the fourth side of the base. Notch the rubber to fit around the magnets, “45” the ends of the rubber pad at the corners and glue in place.


Now for the wiring. Remove the Lexan lens. Examine the bulbs so that you can buy and carry replacements. Then check to see which wires run to which bulb. On my light the wire with the green tracer went to the right rear bulb while the one with the yellow tracer went to the left rear bulb. The solid black wire is a common ground for both bulbs. Since this will be a surface mounts light, drill a hold 1/4” in diameter through the back of the light housing about a half-inch above the base — and centered. Install a rubber grommet (available to most hardware stores) and feed the three wires through it. Now, unless you want to paint the light to match your car’s body color, you are through with the light unit itself.


O.K., it’s time for the final hook-up. On BNIs and BN2s three lines feed the rear lights and run into two single bullet connectors and one double bullet connector located at the left rear corner of the trunk—right where the bumper braces are bolted to the body. The line running into the double connector (red wire) powers the parking/running lights and the license plate bulb. You will not need to touch this wiring. One of the single bullet connectors (white with purple tracer) powers the left rear brake and turn signal; the second (white with brown tracer powers the right rear brake and turn signal. Pull the wires from the single connectors and reconnect the two circuits using the two double connectors instead.


I bought my connectors from Healey Surgeons (part number ELE-0l6). You will also need two bullet connectors (part number ELE-013). Solder a bullet connector to the end of the green tracer wire from the new brake light and one to the cud of the yellow wire. Once things have cooled down, insert the connector attached to the green wire into one of the openings of the double connector linked to the right-hand brake and directional lights (white with brown wire): the end of the yellow wire goes into the double connector for the left hand lights (white/purple).


Note that there is a black ground wire coming from the car’s left rear light unit. Follow this wire and connect the black wire (common ground for both bulbs) coming from the new third light to the same place where it attaches to the body. Turn on the ignition, hit the brakes and test the light. You are now in business — almost.


Unplug the two bulb leads from the new double connectors and detach the common ground wire. Mount the light along the upper edge of the trunk lid centered between the hinges. Open the trunk and feed the three wires through the gap into the trunk. At a point where the wires are about a foot or so inside the trunk, cut each of them to uneven intervals of about 3-4 store buy 3 male/female spade crimp-on wire connectors. The ones I bought have plastic coverings and the male side is a different color than the female side.


On the two color—coded bulb leads coming from the new light, crimp a male lead on one and a female lead on the other. Crimp the corresponding male/ I female connector on the same color—coded wire that will plug into the newly installed double connectors.


You can see where we’re going here. We want to ensure that we don’t mix up the right and left bulb leads to the new light when the light is disconnected/ reconnected. Obviously, the male/male ends of the female/female ends won’t connect, we’ve cut the wires at different lengths so they, also, won’t match up and the male and female ends ale different colors. Crimp on the third connector to the black common ground wire ends. Now, reconnect all wires — and, we’re done!


Here’s how the set-up works. When you step on the brakes in a normal stop situation, both bulbs of the new unit light up with the car’s regular brake lights. In the case of turns, you flip the trafficator switch on the steering wheel for, let’s say, a left-hand turn. The left rear regular light starts blinking and so will the left bulb of the new unit. If you now apply the brake, the right rear brake light comes on and so will the right bulb of the new unit — while the left bulbs continue to blink until the turn is completed and the trafficator switch cancels.


You have now added a rear safety feature to your car without permanently altering anything for a total cost, including taxes, shipping, etc., of under $20.


(If you want the third brake lamp to operate independently of the directions—i.e. only when the brake pedal is pushed—ignore the snap connectors in the trunk, and, instead join the yellow and green wires from the lamp and solder both to a common bullet connector from hardware store as shown in Figure 2. Solder another bullet connector to a common wire, and run that wire through the right hand side of the cockpit and into the engine compartment. Join the common wire to the two leads from the lamp using a barrel connector and ground the other wire from the lamp. Jack up the car and locate the brake lamp switch on the lower right hand side beneath the junction of the forward brake lines. Crawl under the car and note two wires running into the switch. One supplies power from fuse A4, the other runs to relay terminal #5. When you hit the brakes, hydraulic pressure closes the switch and power runs to the relay and out to the rear brake lamps. Connect the common wire from the third lamp to the switch terminal leading to the relay. Now when you press the brake pedal, all three lights will be illuminated. Even though the lines to the brake switch are not hot unless the ignition is on, it’s still a good idea to disconnect the battery - Ed.)


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