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3rd brake light installation...

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I just finished installing a third brake light for added safety. As I'm not particularly concerned about originality on my '70 Avanti it seemed a good addition...especially considering that Avanti taillights have never exactly been paragons of brightness...and I have LED board taillights already.

I experienced a roundabout way of accomplishing this with a couple of twists and turns along the way. Why Avantis are so peculiar about doing anything to them is beyond me...nothing really goes easy...it always seems to take two or three times to get it right. But...that's not the point of this.

My car has a rear defogger blower which complicates any installation as any light will at least somewhat block the blower fan's coverage.

Originally I tried the easy way...a third brake light designed to attach to the inside of the back glass by use of double-sided foam tape. No matter what, the tape refused to stick. I tried several types of double faced foam tape and none would stay more than one night with the car in the garage. They likely would have lasted even less time out in the sun. No matter how well I cleaned the glass with an alcohol solution the light would not stick.

If my car did not have the rear defogger, it would have been easy to make a base or pedestal for a light but that wasn't an option. I found a different LED brake light on Amazon.com for $32.99 that had a bracket I felt would work. I obtained one and it looks good...


The design was exactly what I needed but the dimensions were off considering the area it needed to be mounted in. Using some scrap 1"x2" wood I had lying around, I cut two pieces...a base to mount on the rear wall under the back glass and another, smaller piece to mount the light bracket on. I covered each with matching vinyl I had left over from having the doors and package shelf done and attached the light to the assembly...




Once I was satisfied with it I attached it with screws to the rear wall and angled the light to the glass...


I do have to accept some interference with the rear defogger but I expect I'll need the brake lights far more than the defogger.

As far as wiring goes, I wired it directly to the brake light switch. As I have a mechanical brake light switch it was a simple matter of tapping into the lead that activates when the pedal is depressed. I ran the wire under the door sill, back under the rear seats and fished it through to the trunk along side the wiring harness and connected it to the third brake light.

An alternative method of wiring would be to use a logic module and tap into the wiring harness to the rear brakes lights. As the Avanti uses the same lights for brake, running and turn signals, the module is necessary to make sure the center mounted light only works with the brakes and doesn't flash with the turn signals. I felt that wiring directly to the brake switch was the more positive, better method.

If you have the original type hydraulic pressure activated brake light switch you can tap into that. I believe it's a red wire with a white tracer on it under the dash. Using a test light and pressing on the brake pedal can confirm the correct wire.

Now...the absolutely easiest way to install a third brake light is to buy a license plate frame with the light built in. That's simply a matter of mounting it and running the wire out of the same hole the license plate light runs. The issue with that is the license plate is fairly low mounted on the Avanti and pretty much negates the third brake light's usefulness.

I'm pleased to have the light installed and it seems...at least visually...to make a difference. Hopefully I'll never have to find out.



Edited by Gunslinger

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I like your clear directions, especially about wiring it. I bought an auxiliary light some time ago, and when I get around to installing it think I'll use the hydraulic pressure activated brake light switch, find red wire with a white tracer on it under the dash and do it that way.

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