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Old 02-16-2015, 10:37 PM   #1
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Trailer wiring

At some point I will want a trailer. Before I get too advanced with construction, I want to do the trailer wiring. I figure a single power wire with relays tripped by the power at the rear light clusters. Given that the cable needs to carry enough power to light two reds, two ambers and possibly side lights too, what gauge of wire should I use?

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Old 02-17-2015, 03:29 PM   #2
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Hello.

I think you can use 12 gauge. For your power to the relay you can use 10 or 12. It might be a pretty long run from the battery. 12 would certainly be good from the relay to the trailer plug. You should't need a relay for the signals but you might have to upgrade the flasher to a heavy duty one I don't know. Try it and see if the current flasher would work. You can use a relay for the brake lights as well if you want to. I would think you can get away without a relay there but I would use 12 gauge there also. Better too much than not enough.
Make sure you use a heavy wire to ground the relay too. Any questions just ask. Good luck.
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Old 02-17-2015, 05:22 PM   #3
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I was thinking of taking the relay power from the existing lights then taking light power from the trailer from the single power cable. I fancy 10 gauge but am not sure its heavy enough.

I suppose the real thing is to ask Avis, hertz and uhaul how much power their car trailers pull. Brake connections are A whole other game
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Old 02-17-2015, 07:48 PM   #4
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I'm not so great with electronics but what sort of lights are on the trailer and the bus?

I know when converting my motorcycle from regular bulbs to LED I had to get a flasher relay to get them to work properly. I'm not sure if you'll have to do such a thing for wiring up a trailer connector.

As for getting the trailer wired up, you can go either 4 or 7 pin setup. Does the trailer you plan on hauling have brakes? If it's over a certain weight they're required in most states I believe. If the trailer has brakes you'll want a brake controller and you'll need to extend the wiring in that device as well.

I'd try to wire for a 7 pin connector personally, plenty of diagrams and tutorials online that should show you how to do it. Unfortunately wiring trailers to buses doesn't seem too common so you probably can't just find a connector kit so you'll have to do some cutting most likely, try to plan it out and do as little harness cutting as possible!
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Old 02-17-2015, 07:49 PM   #5
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I'm planning on renting trailers. Not much need to own one when all I'll be doing is transporting my day to day vehicle to temporary home sites
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Old 02-18-2015, 12:48 PM   #6
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10 gauge

10 gauge is more than sufficient. 10 from the battery even on a long run is good. 12 from the relay to the trailer plug will be plenty. OEM setups don't even go that heavy. You will be fine.
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Old 02-18-2015, 06:38 PM   #7
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We only use 10 ga on the ground and charging wires in a 7 pin connector.

The rest are 14 and 16 ga but yes bigger is better.

Most full size buses have extra runs to the back of 12 ga. They were used to run the amber and red lights at the top for school bus dutys. The amber and the red used two independent circuits, so 2 separate 12 ga wires.

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Old 02-18-2015, 06:42 PM   #8
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Ahh... The top lights will be extra brake and turn signals. I have plans for them and plans also to add a hazard flasher that doesn't exist on my bus
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Old 07-31-2016, 11:39 AM   #9
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Going to revive this tread a little.

I am at the point in the rear electrical that I want to add trailer electrical outlets to handle most trailers I plan to pull. The most common would be a tow dolly, rented, and I think most of those have the flat 4 pin connector. I want to wire up a combination 7,5,4 pin adapter to handle most of the options.

With that said, I have a concern. If there is live battery power, ground and connections to all of the lighting circuits, wouldn't someone be able to just jump several of the pins together and fry your bus electrical system? If so, how could you prevent that other than a locking cap which I have never seen?
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Old 07-31-2016, 11:58 AM   #10
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Quote:
Originally Posted by RHOMBUS View Post
With that said, I have a concern. If there is live battery power, ground and connections to all of the lighting circuits, wouldn't someone be able to just jump several of the pins together and fry your bus electrical system? If so, how could you prevent that other than a locking cap which I have never seen?
Fuses. Properly rated fuses.
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Old 07-31-2016, 12:04 PM   #11
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Do you have enemies? Why would someone do that? You can protect with fuses.
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Old 07-31-2016, 12:18 PM   #12
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No enemies but my own paranoia really.

So then since I'm assuming the bus already has fused circuits for all of the lighting at the rear, can I just splice into those wires?
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Old 07-31-2016, 01:27 PM   #13
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Call Hopkins (hopkinstowingsolutions.com)+ tell them what you are doing. Bus to trailer wiring can get funky with seprate brake + blinkers going to a single bulb. I had one of their splitters. It worked odd-the parking lights would stay on. I called tech support + told them what I had. "Oh-you want model XXX. Give me your address + we'll send you one." They did-FREE!!! They make some good multi style all in one units. Heres a kit for an example.
Negative Input Short Proof Power Converter

Another suggestion. etrailer.com. Can't their selection or prices.
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Old 07-31-2016, 03:36 PM   #14
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American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies and wire breaking strength
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