Trailer Brake Relay

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=143043
Printed Date: April 30, 2024 at 10:38 AM

Topic: Trailer Brake Relay

Posted By: dranck01
Subject: Trailer Brake Relay
Date Posted: June 10, 2017 at 3:17 PM

I am unsure of where I should be posting this. Let's see if this will yield any results. I have wired up my trailer using relay for the turn signals, the tail lights, the reverse lights comma and now am needing assistance with my brake relay wiring. As I am sure you are aware the brake signal comes from the turn signals. What I am trying to accomplish, is to activate the brake relay with both turn signals. I have scoured the relay wiring diagram section, and cannot find what I am looking for.

All of the relays are standard single pole double throw relays. I am using the tail relay configured as a normally closed activation. All else is configured as normally open. I am using a battery in my trailer to supply current to the trailer lights.

Any assistance on this matter would be greatly appreciated. If my post is confusing, please let me know.

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Dennis D. Ranck

Replies:

Posted By: the12volt
Date Posted: June 12, 2017 at 8:52 AM

If I understand you correctly, you only want 12V+ sent to the brake relay when both turn signal lights have power as they would when the brake is applied by the tow vehicle. If so, you can use two additional relays to accomplish this as follows:

relay #1
85 to left turn signal positive
86 to ground
30 to fused 12V+
87 to relay #2 terminal 30
87a not used

relay #2
85 to right turn signal positive
86 to ground
30 as described above
87 positive output to brake relay
87a not used

The only time there will be 12V+ on terminal 87 of relay #2 is when both relay #1 and relay #2 coils are activated.

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Posted By: dranck01
Date Posted: June 12, 2017 at 11:25 PM

In running this scenario through my head, it appears as though it will work accordingly.
Yes, what you are describing is what I am attempting to accomplish.
Yes, what you are describing is what I am attempting to accomplish.
I will order more relays, and then give this a try. I think this is it. Thank you.

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Dennis D. Ranck

Posted By: dranck01
Date Posted: June 18, 2017 at 1:23 AM

I just configured the 2 relays as described, and all works as it should. I knew it was really simple. Thank you.

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Dennis D. Ranck

Posted By: the12volt
Date Posted: June 19, 2017 at 7:34 AM

Good deal! You're welcome.

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Posted By: davep.
Date Posted: July 05, 2017 at 11:33 PM

What happens when one side is brake, and the other side is flashing turn-signal? The brake relay will activate off/on with the blinking turn signal. I don't think that's what you want.

Independent BRAKE lights on the trailer need a brake-only circuit directly from the brake light switch in the tow vehicle. Or strange things happen when you brake and signal at the same time.