Join Date: Nov 2001
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Re: Turn Signal for CJ
I can't say about every vehicle made, but I do know how the side markers work on my CJ, same as a lot of others.
Each front side marker is a single filament bulb. It is wired with one lead to the turn signal power and one lead to the power for the parking light, it has no ground. The front parking/turn signal uses a dual filament bulb each filament provided with a power source and a common ground. If the parking lights are on, the side marker lamp gets power on that wire from the parking lamp power. The other side connected to the turn signal becomes a series circuit to ground with the turn signal filament in the front parking/turn signal bulb. The side marker, being much smaller wattage, glows while the second filament in the parking/turn signal does not.
In a similar fashion, when the turn signal comes on, the side marker gets its power from the turn signal circuit and becomes in series with the front parking lamp filament for the source to ground and flashes WITH the front turn signal.
Now, if the parking lights are on, using the front turn signal filament for a source to ground, and the turn signal comes on, the side marker now looses it source to ground and has 12 volts on each side so it goes out. If the parking lights are on, the side marker flashes OPPOSITE, or alternate, to the front signal, being off when the front turn signal is on and on when the front turn signal is off.
The rear side marker is wired with one wire to the tail light circuit and one wire to ground. It does not flash with the turn signals.