3rd Brake Light

3rd brake light not working at all I have 12v input to the Ballast resistor, how can I tell if the Ballast is bad or the lamp . Tese are expensive parts and need to know if their is a way to troubleshoot the ballast

K2 CHECK THE VOLTAGE AT THE LAMP CONNECTOR


Hi-Mount Stoplamp C410


Apply the brake.

Measure the voltage between hi-mount stoplamp C410, circuit 569 (DG), and ground.


Is the voltage greater than 10 volts?
Yes
GO to K3 .

No
REPAIR circuit 569 (DG). TEST the system for normal operation.
K3 CHECK CIRCUIT 57 (BK) FOR OPEN

Measure the resistance between hi-mount lamp C410, circuit 57 (BK), and ground.


Is the resistance less than 5 ohms?
Yes
REPLACE the hi-mount stoplamp bulb. TEST the system for normal operation.

No
REPAIR circuit 57 (BK). TEST the system for normal operation