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Wiring for 7-pin trailer plug

TedStryker

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1993 Explorer 4x4 Limited
Howdy,

I have a '93 Limited. It is currently wired with a "Flat-4" connector. I just acquired a tent trailer and would really like to be able to charge the battery while driving. This, of course, requires a 7-pin RV connector. I have truck-side 7-pin connector, and have wired the lights. (Works good.) For the 12V aux pin, can I just run a line from the battery and underneath the truck?

All ideas and suggestions welcome. Many thanks.
 



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BKennedy

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TedStryker

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Great, thanks. Definitely need a fuse/breaker.

A buddy pointed out that I'd probably want to set it up to that it's only powered when the alternator is running. Any thoughts on how to best do this?
 






BKennedy

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You would have to wire it with a hi amp relay with the "trigger" power (85) coming from a on in run only wire. Use a wire for a non-essential component, like cruise control. It only draws enough to trigger the relay, less than 5 amps. Here is a wiring diagram for a relay setup. You don't need the switch or the ground from the accessory (charging wire).
RelayWiring.gif


I have wiring that charges the Explorer battery while its being towed by my RV. It has a 40 amp auto-reset breaker and a diode to keep power going one way, from the RV to the Explorer. No relay, as I am not concerned about the towed vehicle draining the towing vehicle battery. If I am going to leave it parked for an extended period of time, I unplug the connector. That way, if you ever tow a cargo or horse trailer that has loading lights, you don't need to have the towing vehicle's engine running to use the lights.

My Silverado came pre-wired for towing and it has constant 12 volt power to the plug with no diode or relay. Never had an issue with draining the battery while towing.
 






TedStryker

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This is excellent. Really appreciate the help.

I know my question is not really Explorer specific, but this board always comes through for me. Will let you know how it goes.
 






TedStryker

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Ok, I just came up with another question on this little project.
Looking at the RV wiring diagram, it does not appear that there is any sort of device controlling the charge to the battery. The 12V power supply appears to go directly from the RV plug to the battery. It seems like when the RV battery is very low, it would draw a lot of current from the vehicle. Is this something I need to worry about?

The RV has a "converter" for charging, but it looks like that's just a rectifier which charges the battery when it's plugged into 110V. It seems like there should be some kind of 12V charge controller for the RV battery when it's charging from the tow vehicle....
 






BKennedy

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Correct, the converter is just for charging and running the electrical system while plugged into whatever shore current its rated for (15, 30, 50 amp service), usually while "camping" in a RV Park. The 12V power supply from the towing vehicle to the towed vehicle is usually a direct connection, using the towed vehicle's alternator to charge all batteries while in transit. Sounds like using a relay setup would work best for you so there is no chance of running down the towed vehicle's battery. It would be the plug it in and forget about it solution.

If you are running the RV battery down while dry camping, you should run the generator for 20 minutes to charge the battery, or plug your towing vehicle into the RV with the engine running for 20 minutes, and/or get a solar system.

I used to tow a 12' pop-up trailer with the Explorer before I purchased a class A RV to tow the Explorer. I mounted a small 40 watt solar panel to the roof and ran the wires to an inexpensive solar charger and added another battery. Worked great. The small trailers are better for off your favorite forest road type camping, the motorhomes are better for everything else. My latest class A has 4, 6V coach batteries and one chassis battery with a solar system and a "whole house" Xantrex inverter as we mostly dry camp. I need to upgrade the solar panels to about a 300 watt system and I should be able to dry camp for as long as I want as far as electricity goes. The RV tow plug's 12V constant comes from the coach batteries. There is no way the Explorer battery is going to pull enough power to run them down.
 






TedStryker

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Great, really appreciate the helpful info. Very useful. Our camper is a small pop-up... I don't expect to be running the battery very low - I'm converting all lights to LED, will run the fridge on propane while parked and don't expect to be in the same place for more than a few days. Hopefully I can recharge sufficiently through the tow vehicle.

I installed the fuse and relay today. I didn't have time to set up the 7-pin, but I tested the relay and it seems to be working just like it should. I was having a tough time finding a good wire for the switch power; I wasn't able to find a good wiring diagram and the wire bundles are so tight with very little play. In the end, I decided to use the "ignition on" wire for the stereo. Worked great.

Will get back to the project in a few days and finish it up. Thanks again.
 






BKennedy

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Your welcome.
The stereo wire should be fine as its not a critical component. When you stated you set up the fuse and relay, if you wired a fuse into the wire coming from the stereo wire, its not necessary as its already fused at the inside fuse box. Adding fuses to already fused lines can cause issues. If you were talking about the wire coming directly from the battery to the relay, you should have a 40-50 amp auto reset breaker in line, not a fuse.
 






TedStryker

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My apologies for the confusion. I did use a 40 amp auto reset breaker (not a fuse) on the wire coming from the battery to the relay. I did not install a fuse on the wire coming from the stereo.
 












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