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Topic Review (Newest First)
09-27-2013 10:23 AM
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.

09-25-2013 05:24 PM
EOD Guy 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.
09-25-2013 05:18 PM
EOD Guy 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)
09-25-2013 12:48 PM
Joe G 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.
09-25-2013 12:20 PM
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 | ). 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.
09-25-2013 09:55 AM
Free hand drawing

Robin, I'm not sure what you're using for a pilot switch for your blinkers. But I understand what you're trying to do. Here is a free hand drawing in ladder logic that should work fine. I don't do computer drawings because it takes me forever. This will have the required load to use a conventional flasher versus the electronic. (Doesn't flash the relay) Just two relays (KISS) Hope this will work in your application. Nolan
09-25-2013 05:17 AM
John long
Originally Posted by Joe G View Post
I think you're on the right track, but you had an unnecessary relay and a few wires crossed.

I would recommend this:

Note: This circuit will only work with an electronic flasher.

Hope this helps.....
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?

09-25-2013 03:51 AM
EOD Guy Joe G's diagram is sound and it will interrupt the brake on one side and allow it to blink while the other brake stays lit. What model vehicle is this on?
09-24-2013 10:03 PM
robin58 Olnolan, 4 bulbs. That's all I am trying to wire in. 1157 type. 4 wires going to them: brake, lt, rt, parking lights. Pl are irrelevant as obviously work. As stated above,I am simply looking for 4 lights on when braking, and each pair flashing when using turn signals. Without an adapter or relay in there, the lights obviously wouldn't flash with turn signals if the brakes were lit as they would still be getting 12v from the brake switch.

Fwiw, I've found this: Tail Light Mods 4 which appears to have used the exact same method I came up with but I still think Joe G's method should work too. I'll just wire it all up and see what happens...
09-24-2013 09:31 PM
Pilot switch

Robin, If you draw a diagram with the pilot devices that you wish to control your brake and turn signals from, then there are many capable folks here that can add a relay from the the pilot device to the load device, but what you have here is an unconventional brake, turn signal circuit. On every automobile running, brake and turn signal circuit I've ever worked on or designed the pilot device is a combination of the turn signal switch and the brake light switch which renders a 1) running light circuit 2) left brake and turn signal circuit 3) right brake and turn signal circuit. Your wiring diagrams are incorrect and not conventional to automotive standards. Please clarify. Nolan
09-24-2013 08:44 PM
robin58 Sorry, but my brake and turn signal wire are NOT the same. My wiring harness has separate brake and turnsignal wires. There is no trailer involved as I stated above. I used a trailer wiring ADAPTER as is farly commonly done when faced with 4 wires (parking lights, left turn, right turn and brakes) and wiring them to bulbs that do not involve a separate brake light, I.e. 3 wire. And yes I know there is a white as ground on some adapters but for obvious reasons I omitted that as it is irrelevant on wiring a car which has been correctly grounded. Those cheap adapters work, but tend to burn out. Hence my desire to use relays.
09-24-2013 08:13 PM

None of these cicuits make any sense because the turn signal wire and the brake light wire are the same. Brown is running lights on both sides, green is right turn signal and brake lights, yellow is left turn signal and brake lights, white is the ground. You're problem is a bad ground or trailer ball ground. Are you wiring brake, turn signals and running lights on a car or on a trailer please clarify.The way ya'll have it drawn up is a five wire circuit. 1)gound2)left turn3)right turn4)brake)5)running lights. Nolan
09-24-2013 06:32 PM
robin58 I can see that makes more sense than my concept
09-24-2013 06:20 PM
Joe G I think you're on the right track, but you had an unnecessary relay and a few wires crossed.

I would recommend this:

Note: This circuit will only work with an electronic flasher.

Hope this helps.....
09-24-2013 05:57 PM
robin58 Car, but I had been using the cheap/easy way to get brake lights and turn signls working on 4 rear lights by using a trailer adapter.

My logic was that the way I drew it up, the brake lights would stay powered up on the side not using the turn signal, but the circuit from the turn signal would then take over through the relays needed whichever direction I turned.

I realize with the harness I have (keepitsimple) I could wire one pair as brake lights, one pair as turn and not have an issue, but what I am trying to accomplish is 4 brake lights and then have either pair also act as turn signals.

Electrickery has never been a strong point of mine so any suggestions would be appreciated...
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