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Old 09-25-2013, 01:20 PM
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Originally Posted by John long View Post
It appears to me this will work but I am not sure why you are doing it. Is this a way of wiring turn signals because you are not running a conventional turn signal switch?

This is a fairly common problem encountered with 3rd party wiring harness installs and custom taillights as revealed by Google searches.

If you have one dual filament bulb on each side serving as parking light and then the brighter filament serving as brake/turn signal, you have 1 wire too many to hook up to your bulb on each side. The most common circumvention is the one I took to start with: using a trailer harness adapter designed to work with towing vehicles that have a separate circuit for brake lights and turn signals (mostly imports - eg this type of adapter: Hopkins/Import tail light converter (48845) | Tail Light Converter | AutoZone.com ). This allows the same bulb (usually an 1157 or similar) to serve the dual purpose.

My particular situation was complicated because I had installed bedroll lights into my 53 Chevy's truckbed. Due to a local law the turn signal must be within X distance of the brake lights meaning I couldn't just designate one pair of lights as brake and one pair as turn signals. Sure I could have ripped out the bedroll lights but really liked the extra illumination from the rear.

As I have stated a few times, the adapter method worked, but they aren't exactly long lasting hence my desire to take a better route of using relays to accomplish what I needed.

Of course if you know of a simpler method, I am all ears but I sure haven't seen a solution anywhere.

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Old 09-25-2013, 01:48 PM
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The simplest most reliable solution is to have a turn signal switch that combines the turn/brake signals, but I'm assuming that you are still running your original steering column and turn switch so that's not an option.

Joe G.
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Old 09-25-2013, 06:18 PM
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Joe G's diagram is what you need.
You can use some Omron relays out of modern cars, Jeeps and Mopar use these, I pay .50 cents per, at my local junk yard, They are super small and are wired exactly the same as the larger bosch type. (the six measure 3/4 inch by 1.5 inches)
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Old 09-25-2013, 06:24 PM
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If you want to completely wire it using a toggle type switch, you old column mounted TS switch might be converted to a simple on/off function and would work well with this diagram. My version has been installed in two vehicles, that I know of.
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Old 09-27-2013, 11:23 AM
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Originally Posted by robin58 View Post
I had been running my 4 taillights with a simple trailer harness 4 to 3 adapter but it seems somewhat erratic (maybe exceeds amperage allowed?) so am going to replace with relays.

Is the attached a workable way of accomplishing this? For the sake of drawing ease I omitted the parking light circuit as that isn't an issue.

Intermittent sounds like a wiring quality issue not excessive amps. Somewhere there is a wire or a connector that is not making a consistantly constant connection. First suspect I'd be looking at is the ground. If the trailer lights use the trailer chassis as a common ground then there needs to be a wire connection between the trailer and the tow vehicle. The hitch cannot be depended upon to provide this connection. If the lights all ground to a return wire rather than the trailer chassis then the problem is somewhere in that circuit.

Exceeding the amperage of an electrical system in the case of lights will result in the lights being dimmer than their Lumen's rating, the wiring may be warm to the touch, or circuit fuses will burn out on a regular basis, for turn signals the relay will speed up.

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