I just received a letter from a customer regarding a problem he was
having with his taillights. He wrote:
“When my lights are off and I step on the brake the brake lights work
great, but when I turn on the lights they are always bright.”
This is one symptom of a very common problem. Somehow the brake and
taillight wires are shorted together. To fix this check inside the
taillight sockets. This is this is where the problem usually is. The
spring could be bent over and shorting out the two wires together or
they could be misaligned and touching. Also be careful because many
times the problem disappears when the bulb is taken out! I have even seen
on more than one occasion where one of the filament is blown and
touching the other filament causing the short inside the bulb itself.
An even stranger problem can happen if one of the front lights is
shorted out. The lights may seem to work properly but when you switch
the turn signal on the shorted side it will look like you are running
4-way flashers. This is caused by the turn signal power back-feeding
through the park/taillight circuit in the shorted out light.
The main point is to check and double check your dual contact sockets.
It is very close quarters in there.