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Old 09-24-2013, 11:46 AM
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4 to 3 wire taillights

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.

TIA.
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Old 09-24-2013, 04:39 PM
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If I read it correctly, when you step on the brake you energize R1 and 30 is connected to 87a 87a is connected to R2-87. There is no pwr to R2-87 unless you turn the turn signal on.
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Old 09-24-2013, 04:55 PM
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grounds

The trailer lights are wired in parallel with the towing vehicle tail lights.
If the trailer adds too must load (not likely) just replace the trailer bulbs with LED and replace the TS flasher with an LED flasher.
Those diagrams won't work because the TS switch in the towing vehicle controls the brake light circuit.
Typical problem with trailers is a poor ground. This causes all kinds of strange things. Make sure the trailer has a good ground to the towing vehicle.

vicrod
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Old 09-24-2013, 05:09 PM
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This is quick and not bench tested..... but might be along the right line...... my concern would be when the brake light is lit and the turn sig is on........ the turn sig pwrs the relay and disconnects the NC circuit which interrupts the brake light........ when the flasher can interrupts the turn sig and drops the relay and the brake light comes back on...... is there enough of a delay to allow the thing to blink properly. Only way to tell is to bench test it
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Old 09-24-2013, 05:11 PM
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just read this a little closer..... is this for a trailer or a car?
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Old 09-24-2013, 05:57 PM
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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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Old 09-24-2013, 06:20 PM
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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.....

Last edited by Joe G; 09-24-2013 at 06:37 PM. Reason: Corrected 87 and 87a relay terminals
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Old 09-24-2013, 06:32 PM
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I can see that makes more sense than my concept
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Old 09-24-2013, 08:13 PM
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?????????????

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
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Old 09-24-2013, 08:44 PM
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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.
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Old 09-24-2013, 09:31 PM
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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
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Old 09-24-2013, 10:03 PM
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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...
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Old 09-25-2013, 03:51 AM
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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?
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Old 09-25-2013, 05:17 AM
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Quote:
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?

John
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Old 09-25-2013, 09:55 AM
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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
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