Trailer wiring
#3227264
04/15/24 08:54 PM
04/15/24 08:54 PM
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Posts: 1,462 Martinsville, IN
cdwmotorsports
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I'm doing Dragweek this year (1972 Demon) and I'm wanting to isolate the car wiring from the trailer wiring. I once heard it could be done with relays. If anyone has any suggestions, tech articles etc. I'd appreciate the help.
Last edited by cdwmotorsports; 04/15/24 09:07 PM.
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Re: Trailer wiring
[Re: TJP]
#3227282
04/15/24 11:24 PM
04/15/24 11:24 PM
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cdwmotorsports
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Going to have to be a bit more specific, IE: Are to towing a trailer with the car, or towing a trailer with the car in it? I'm towing a trailer with the Demon during Dragweek. I dont want to burn down my stock wiring nor do I want to have issues with the switch.
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Re: Trailer wiring
[Re: cdwmotorsports]
#3227333
04/16/24 03:12 AM
04/16/24 03:12 AM
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Cab_Burge
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Last edited by Cab_Burge; 04/16/24 03:14 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Trailer wiring
[Re: Cab_Burge]
#3227505
04/16/24 04:12 PM
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TJP
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I'm not understanding the need for the relays One is still going to have to use a plug to disconnect the trailer from the car unless I'm missing something. I also don't understand the need for a #4 to 6 gauge wire Unless your trailer looks like the house in Christmas Vacation I'm totally baffled.
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Re: Trailer wiring
[Re: TJP]
#3227577
04/16/24 09:14 PM
04/16/24 09:14 PM
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Dcuda69
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I'm not understanding the need for the relays One is still going to have to use a plug to disconnect the trailer from the car unless I'm missing something. I also don't understand the need for a #4 to 6 gauge wire Unless your trailer looks like the house in Christmas Vacation I'm totally baffled. I agree! Trailer description please. If there are no brakes on the trailer a simple 4 wire plug(wired correctly) and good trailer grounds....done.
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Re: Trailer wiring
[Re: Dcuda69]
#3227721
04/17/24 02:33 PM
04/17/24 02:33 PM
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hooziewhatsit
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Sounds like he doesn't want to run the current for the trailer lights through the wiring in the truck?
Having the 4 wires to the trailer triggering their own relays would work. Though it would be overkill, unless he has a few kw of lights.
I have a small fuse block inline with the wiring to the trailer. If a wire on the trailer shorts out, it will hopefully blow that fuse, keeping the lights on the truck functional.
If you ever find yourself in a fair fight, your tactics suck.
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Re: Trailer wiring
[Re: hooziewhatsit]
#3227725
04/17/24 03:24 PM
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340SIX
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Sounds like he doesn't want to run the current for the trailer lights through the wiring in the truck?
Having the 4 wires to the trailer triggering their own relays would work. Though it would be overkill, unless he has a few kw of lights.
I have a small fuse block inline with the wiring to the trailer. If a wire on the trailer shorts out, it will hopefully blow that fuse, keeping the lights on the truck functional. Maybe I am reading it wrong? I read he had a 1972 Dodge Demon, and wants to tow a small dealer with Demon not truck. His plan I assume is to, pull a small trailer with extra parts, tools and supplies. Small trailer with stuff in case something needed in route. I believe the rules state you must be stand alone vs a chase team to repair Guys toss slicks, drag radial on roof, back seat etc. So they have highway tires on car ect. And how small trailer with tools, parts, few race gas cans ect. He sound be fine with a 4 pin for lights, signals, brake lights on a tiny trailer. (ASSUME) He is towing with an A Body
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Re: Trailer wiring
[Re: TJP]
#3227727
04/17/24 03:32 PM
04/17/24 03:32 PM
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Cab_Burge
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I'm not understanding the need for the relays One is still going to have to use a plug to disconnect the trailer from the car unless I'm missing something. I also don't understand the need for a #4 to 6 gauge wire Unless your trailer looks like the house in Christmas Vacation I'm totally baffled. Read his post again , he wants to isolate the trailer lights from his stock wiring system with relays
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Trailer wiring
[Re: Cab_Burge]
#3227746
04/17/24 05:16 PM
04/17/24 05:16 PM
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crackedback
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same reason and concept putting headlights on a stand alone relay setup, load off the the marginally adequate stock harness.
Last edited by crackedback; 04/17/24 05:16 PM.
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Re: Trailer wiring
[Re: BDW]
#3227752
04/17/24 05:40 PM
04/17/24 05:40 PM
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Joined: Feb 2015
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crackedback
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lots of ways to skin the cat. pick your parts, pay your money. Any additional load on the stock 72 electrical system isn't the way I would go. JMO
Work the approach that suits you best.
Last edited by crackedback; 04/17/24 05:43 PM.
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Re: Trailer wiring
[Re: crackedback]
#3227758
04/17/24 06:13 PM
04/17/24 06:13 PM
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ruderunner
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I use relays, a fuse block and circuit breaker in the manner that Cab describes. But, I tow bigger trailers and occasionally not mine trailers.
The not mine ones are usually sketchy and I got tired of losing my truck lights when plugging in.
An isolated system is easy to install. I put my stuff near the battery to limit the length of high Amp wires to the fuse block.
And yes, the factory wires are taxed by extra lights.
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Re: Trailer wiring
[Re: ruderunner]
#3228076
04/19/24 12:27 PM
04/19/24 12:27 PM
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cdwmotorsports
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Thank you 340six, Cab_Burge, ruderunner and crackedback for reading the entire post and answering or giving input related to the question. I appreciate it more than you guys know. I figured the system Cab described was what I needed but didn't want to presume it.
Cab_Burge do I need to run a wire from the switch all the way back or will just tapping the light wires serve as the trigger? Just ensuring I'm correct that I will only use 3 of the pins on each relay for this project.
Crackedback was it you that built or builds the headlight isolation harnesses? If so is it needed if I'm running LED headlights?
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Re: Trailer wiring
[Re: hooziewhatsit]
#3228078
04/19/24 12:29 PM
04/19/24 12:29 PM
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Joined: Mar 2003
Posts: 1,462 Martinsville, IN
cdwmotorsports
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Sounds like he doesn't want to run the current for the trailer lights through the wiring in the truck?
Having the 4 wires to the trailer triggering their own relays would work. Though it would be overkill, unless he has a few kw of lights.
I have a small fuse block inline with the wiring to the trailer. If a wire on the trailer shorts out, it will hopefully blow that fuse, keeping the lights on the truck functional. Thank you too for the input, I am not one to rely on "hopefully" although a standalone fuse panel was considered.
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Re: Trailer wiring
[Re: FurryStump]
#3228220
04/20/24 08:55 AM
04/20/24 08:55 AM
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So he is talking about the small support trailers the drag week cars tow from track to track. A fused power feed directly from the battery. Then a relay for tail lights, two for brake lights/directionals. Tap into the rear tail light wiring harness to get each “signal” voltage for each relay. Only a small voltage will go through the car wiring. Tap into the driver side brake light wire and send it to drivers brake light relay. This relay output goes to the driver side trailer lights. Do the same thing for the separate passenger side brake lights relay. Then tap into one tail light wire on the car and run it to the tail light relay. The output from the tail light relay will spit and go to BOTH trailer lights. Drivers and passengers sides. Three relays and three splices into the car tail light harness. Thanks FurryStump, that's a simpler setup than I had designed. I had the brakes and turns on separate relays.
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