Cornering Light scheme for Mustang

Brian Fraser 2020


 I have wanted a right turn cornering light for my 1991 Mustang for several years.  Cadillacs have similar lights for both left and right turns as standard equipment. In my case the light illuminates an area I am turning into at night that is not adequately illuminated by the headlights.  The lamps are mounted in two holes in the right front plastic bumper shroud. Light is switched on when the right turn signal is activated. The pulse from the turn signal goes to a relay-capacitor-transistor circuit with a time constant of about 3 seconds so that the light stays on continuously during the turn and then extinguishes about 3 seconds after the turn signal stops.

I decided to use a somewhat unconventional scheme to wire and control the lights. The car is 30 years old and has lived in the Phoenix, Arizona area for as long. The heat in this locale tends to make the plastic electrical connectors brittle, and although I have the car's electrical schematics, I decided to not disturb these old connectors (and their plastic trim coverings) to make taps into the appropriate electrical wires. Instead, I sourced the needed signals directly from the headlight and turn lamp themselves, but  then to work properly,  these signals have to be processed by a custom made controller.

The controller is very simple and was made from parts on hand .  Key parts were:

BOJACK Schottky diodes, 60 V, 5A  (P/N: SR560  (test forward V as 0.215; these can also be general purpose diodes)
Bridgold 20pcs TIP120 TO-220 NPN Darlington Bipolar Power Transistor, 5A 60V HFE:1000, 3-Pin  

Electromagnetic power relay 12VDC, 5A contacts, DPDT with DIN socket, 164 ohm coil
  (YJ2N-GS-8-12VDC) APIELE  X001Z5TU5B


I used 4300 mF and 680 ohms   to  get the right time constant for the Darlington

The parts were mounted on a piece of Masonite. The four terminal posts were made from segments of plastic pipe, 1/2" coupling nuts (10-24) and epoxy fill.  At the bottom is a 6 position barrier terminal strip. The whole thing fits into an aluminum project box with provisions to the keep the board in place and properly insulated.

The box that houses the controller board is a BUD
Industries CU-3008-A Aluminum Electronics Minibox,
7" Length x 5" Width x 3" Height, Natural Finish (
)  The 3" height was easily cut down to 2”so that it would fit under the front seat.

The cornering lamps shown below the right front bumper are Ambrother LED Pods Light Bar 4-Inch 120-Watt lamps (12,000 lumens each). Each consumes about 1.8 amps @ 12.6 VDC  (23 watts each). Both lamps light up during a signaled right turn if  the headlights are on. They go off  about 3 seconds after the turn signal resets.