May 2005 f-150 turn signal blinks fast replaced bulbs are good?

Answer 1

Turn Signal Flash Rate Determination

First here is a primer on how the flashing of turn signals is caused/controlled.

Almost all vehicular turn signal flashing is controlled by a special relay commonly called a flasher.

Inside the flasher relay is a self-actuating switch in which one of the two contact points is mounted on the end of a "bimetallic" [made of two dissimilar metal layers bonded together] strip of metal.

As electric current [measure in Amps (A), or milliamps (mA], flows through the bimetallic strip, the current flow causes the strip to warm up.

The two metal layers in the strip have different "coefficients of thermal expansion" resulting in one side of the strip lengthening faster than the other.

By design, that causes the strip to bend from the heat, which results in the one contact on the strip being moved away from the fixed contact, and thus opening the switch.

This turns off the current to the turn signal circuit and lamp [bulb], thus turning it off.

As the bimetallic strip cools down slightly, it bends back to where it started, thus closing the contacts, energizing the circuit, and causing the turn signal lamp filament to turn ON.

As long as the turn signal control switch on the steering column is closed, the signal flasher relay will continue to cycleopen and closed.

Now to get to the basic original question as to why a turn signal will blink faster, or slower.

The answer is that the rate of the flasher cycle is directly proportional to the amount of current [Amp or milliamps] flowing through the circuit.

The amount of current is caused by the size and conductivity of the filaments in the lamps, and/or the number of lamps in the circuit. The larger the lamp filament the greater the current and thus the flash rate.

The more lamps, the more current flows, thus heating the bimetallic strip faster, and causing it to open, turning off the lamps.

One of the best examples of this is that when a trailer [with turn signal lamps] is added to the turn signal circuit, the flash rate will usually increase, unless the flasher is rated "heavy duty."

For those whose cars and trucks have ordinary flasher relays and who don't like the rapid flash rate resulting with the addition of a trailer, they can replace the standard flasher relay occasionally referred to as a flasher "module" with a heavy duty one.