<VV> 3rd brake light on an early model project (very long)

[Dave Thompson]

Project: 

 

3rd brake light.

 

Specifications:

 

Modify the rear deck turbo emblem to light in the red arrows and work as a
3rd brake lamp.

It will light only when the brakes are applied. 

It will not flash with the turn signals. 

 

Background:

 

The early model rear tail lamp bulbs have two elements. The dimmer of the
two elements, is tail lamp. The brighter element is both brake and turn
signal. Because of that, Chevy ran three wires back to the lamps; tail lamp,
left turn/brake and right turn/brake. 

 

The brake light switch at the pedal connected to 12 Volts. When the pedal is
pushed, the switch connects 12 volts to the brake light wire. The brake
light wire is run from the brake light switch to the turn signal switch
mounted low on the steering column. 

 

The turn signal switch does it's magic and combines the brake lights with
the turn signals. The output if the turn signal switch is left turn/brake
and right turn/brake. From there, these two wires are run back to the tail
lamp sockets. The tail lamp wire feeds from the headlamp switch to the tail
lamps sockets. The lamp sockets, attached to the housings ground to body
when mounted. 

 

Challenge:

 

This means that there is no "brake only" wire at the rear of the car. Both
turn/brake wires cannot be connected to the 3rd lamp. This would be
connecting both turn/brake wires together. This would cause all three rear
lights to flash when either turn signal is activated or the brake is
pressed. Not good.

 

The two wires could be connected to the 3rd lamp through Diodes. These
diodes will block "back-feed" from the left and right wires to and from each
other. However, this would allow the 3rd lamp to flash in a turn signal and
no brake condition. Brakes and turn signal together will cause the 3rd lamp
to glow steady. specifications call for the 3rd lamp to not flash with the
turn signals.

 

Solution:

 

One solution would be to run a new wire from the brake lamp switch to the
3rd brake light. However that will mean jacking the car up and removing the
pan. Running the wire through the interior would be bad craftsmanship.
There's got to be an easier way. 

 

There are electronic modules available that will separate the brakes from
the turn signals. Left and right turn/brake are properly combined and the
output is a brake only connection. This will allow connecting the 3rd lamp
to the existing turn/brake wires at the rear of the car.

 

Project things to do:

 

Investigate red plastic for lens

Finish bread boarding the LED circuit

Design and etch circuit board

Solder and test components

Finish grinding rusty "test" emblem

Assembly of circuit board and lens to emblem Temporary external wiring and
mounting prototype Verify visibility, adjust accordingly Assess styling
quality If acceptable, purchase electronic module grind new reproduction
emblem and install lens and circuit board Permanently mount and wire new
lighted emblem Take photos of the process for later documentation

 

 

Tonight is the last Sunday night before Christmas. Tomorrow morning, I will
clean up my workbench. The project will be put in a box of its own and
shelved until after Christmas. This time of the year my shop becomes the
gift wrapping room.

 

When I return to the project, I will use the above email as a basis to
document my 3rd tail lamp. 

 

Next projects: 

 

Early model rear fake vents as brake and turn signals )by request from
several people) Intermittent wipers

 

I wish all of you here on Virtual Vairs and your families a wonderful, happy
holiday.

 

Dave Thompson

63 Spyder vert

Westminster, CA