Trailer winch battery wiring

Good evening folks.
I just had my 16' dual axle trailer with 4 wheel brakes and all the necessary lights totally refurbished and painted with new flooring and rewired so all this was replaced new. I am now going to install a 12 volt winch now for loading a tractor when it is not running.
For the electrical hookup I have the 7 pin connecter plug setup where the center pin is hot (12V +) but I don't have anything hooked to that pin now, unless the repair facility has the breakaway battery for the brakes connected there. I would like to know how do I connect a battery for the winch to the center pin so the winch battery will be charged but yet not kill the truck battery. I suppose it will be best to have the truck running when using the winch to keep the truck's battery charged. Does this setup require some type of relay or something to prevent the winch from draining the truck battery or how is all that handled? Truck is a 2009 F-150 Ford and the brake controller is the Prodigy Voyager model. I appreciate the help you people here give us that need it. Thaanks in advance for the help . Gene Davis Tennille, Ga.

You can hook the winch wire to one of your live feeds such as the trailer lights. Install a switch for the winch and ground to the trailer. You will need to have your lights on to run the winch but that's the simplest solution to your winch

Tap into the plug on the trailer fuse it with a 30amp breaker at the battery when the winch is needed disconnect the 7 pin connecter plug.

The trailers that we sell that are factory equipped with winches have either 20amp fuses between both the Battery + connection in the harness and also the - ground connection. The last one I worked on had 20 amp circuit breakers instead of fuses. That way, if the winch battery draws down, The fuses blow or circuit breakers open and don't blow any fuses on the truck. (Or melt any wires!) I lean toward circuit breakers. they will automatically close when they cool off, while the fuses are a one-time deal. Meaning if you blow a fuse, the truck can no longer charge the winch battery, but if a circuit breaker opens, it will close when it cools and after that the truck can charge the winch battery up again.

You only need to install a 20 amp breaker, like used under the dash in heavy trucks , put it in between your truck plug and the battery on the trailer. When you winch very much the breaker trips then soon as you get back in the truck and start home it will reset and charge the battery. Been running several like this for years. On the trailer we use heavy batteries and one can winch several minutes .

No light wire is anywhere close to running a winch , only going to blow a fuse or burn up the light wire.

THE CENTER PIN ON A 7 PIN PLUG IS FOR BACKUP LIGHTS.

There is standard wiring information for 7 pole connectors. On the blade type connectors, the positions are the same, just the color of the wires vary between the Utility and RV standards. If your tow vehicle has a factory installed plug the function positions will be as shown. If installed aftermarket positions should be the same if done correctly. You will note there is one blade dedicated to power. I believe you will find the key has to be on to have power on the 12 volt power terminal of the truck connector. This would be used to charge the breakaway battery or other 12 volt needs on a trailer. That is the terminal you should get power for your winch battery from. And yes, a circuit breaker after the trailer junction box is a good idea.

If you plan on doing a lot of winching, you might want to run a separate circuit using at least 10 gauge power (+ and -) wires from the truck battery to the winch battery. This could be a 10 gauge extension cord with clips on the ends you can hook up when winching. That way you don't risk the truck and trailer wiring.


This post was edited by Jim.ME on 06/10/2022 at 03:24 am.

Most trucks the trailer power supply is tied to the key switch. Ford is for sure, I dont have experience with the others.

As others have said, use a 20 amp breaker in your charge line. It is the cheapest and easiest way to isolate the winch battery.

If you need a battery, check with a local heavy truck dealer. They usually have group 31 screw top batteries at a good price.

(quoted from post at 21:59:48 06/09/22) You can hook the winch wire to one of your live feeds such as the trailer lights. Install a switch for the winch and ground to the trailer. You will need to have your lights on to run the winch but that's the simplest solution to your winch

Click to expand...

Lol. That's a pretty "light" circuit to run a winch on.

Unreal some of the suggestions that get offered.




This post was edited by Carlmac 369 on 06/10/2022 at 04:35 am.

Good morning Gene, I owned, bought and sold trailers for years when I was an implement dealer and fought these wiring and charging issues a longggggggggg time lol FWIW here are my recommendations:

1) I would suggest using the standard wiring for those round 7 pin plugs and receptacles where the center is for BACKUP LIGHTS NOT 12 VDC auxiliary power !!!!!!! I would use the 12 volt auxiliary terminal instead

2) Regarding a charge wire circuit so when driving the trucks alternator provides charge to the trailer battery I WOULD USE NO LESS THEN 10 GAUGE WIRE to reduce line voltage drop, even if sure 12 Gauge will work and a lot use it. I just believe in over engineering and line voltage drop reduction which larger wire creates......

3) Overcurrent Protection is required for BOTH truck and trailer batteries, and with 10 Gauge wire I use a 30 Amp auto reset circuit breaker at EACH battery/source. This over current protection for the TRUCK BATTERY may well or may not already be in place using the factory set up ?????????

4) In order to allow the trucks battery and alternator to charge the trailer battery but NOT allow the trailer to discharge the truck battery, you could

A) Use an inline diode so current can flow FROM truck to trailer but NOT from trailer to truck HOWEVER there would be around a 0.6 Voltage Drop across the diode
B) Use a relay so the charge wire circuit is ONLY activated when the truck is running but DISCONNECTS/OPENS otherwise.
C) A or B can be achieved by a factory circuit configuration that provides power ONLY via switch and truck is running but NOT otherwise, if so you can get by without A or B !!!!!!!!1
D) Unplug

NOTES using the 7 pin connector and light gauge wire from truck to trailer via the 7 pin connector IS NOT FOR HIGH CURRENT. Those connectors are ONLY rated for lower current applications and long runs of light gauge wire cause a line voltage drop HOWEVER sure this set up can provide some degree of charging from truck to trailer and is used widely for intermediate to at least trickle charging the trailer battery when driving the truck GO FOR IT but I still recommend 10 Gauge Wire,,,,,,,,, 30 amp auto reset circuit breakers for BOTH batteries,,,,,,,,,,A method to prevent reverse discharge of the truck battery ..

TRAILER BATTERY I would use a DEEP CYCLE battery on the trailer.

Check out the overcurrent protection and reverse current discharge protection that may well ALREADY be a part of the trucks wiring !!!!!! If so it makes things easier and you dont need to worry about much of what I posted. Test voltage at the 7 pin receptacle on the truck to see if the 12 volt auxiliary pin (NOT center backup light pin) goes hot when truck is on but NOT when off and if so you don't need much else other then wiring and over current protection from trailer battery to the trailer plugs 12 volt aux terminal

DEDICATED HARD WIRED GROUNDS CAN PREVENT A TON OF TRAILER ELECTRICAL PROBLEMS

Best wishes take care

John T

Thanks everone for these suggestions and info. I do in fact already have #10 wire installed and have a 20 amp circut breaker in the hot line from the truck battery. It is located in the #10 wire about 18 inches from the battery and since I moved this controller from my 1997 GMC truck to this Ford which did not have the factory towing kit I had to install all the wiring myself. The brake circut is # 10 wire also and has a 20 amp breaker in it about 18 inches after the battery connection. The ground wire is also #10 wire from the battery all the way through the plug contacts to the trailer so that there is a ground wire connected to the trailer frame. If I used the idea from John T for a relay, where would the relay pick up its turn on power from? Would it connect to the charging feed wire just before it connected to the winch battery? Or if a diode is better, what size diode would be needed? Also there are no back up lights on the trailer. If I have the truck running while using the winch will the truck system be in danger?

Thanks, Gene

Good questions:

1) If I used the idea from John T for a relay, where would the relay pick up its turn on power from?

One place FOR THE POWER would be direct off the truck battery POS terminal protected with the proper size fuse or breaker. The relay power output would connect to the charge wire circuit back to the trucks 7 pin connector terminal

One place for the PICK UP OR ENGAGE OR SIGNAL to activate the relay I CANT SAY WITHOUT A SCHEMATIC but a location that turns hot ONLY when the truck is running or key is on could suffice to activate the relay. Maybe some Ford owner can tell you the location SORRY I dont know

2) Would it connect to the charging feed wire just before it connected to the winch battery?

Above I was talking about the POWER feed from the TRUCK battery for the relay...At the winch battery you just need overcurrent protection for the charge wire circuit. I envision the relay up at the truck battery and when its activated the charge wire circuit goes to the trucks 7 pin connector then the trailers connector then the trailer battery via a circuit breaker.


3) Or if a diode is better, what size diode would be needed?

A diode rated for 50 amps (depends on charge circuit max amps) at least 50 or 100 volts should suffice. If its used (instead of a relay) in the charge wire circuit from truck battery back to trailer battery if wired correct it lets charging current flow to trailer battery but NOT allow discharge. There is a 0.6 or so voltage drop across the diode but a long wire run back can also cause a voltage drop. These type of charge wire circuits are for lower current to charge or trickle charge the trailer when driving NOT so much to power the winch. A simple inline diode is soooooooo much easier to allow charging but not reverse discharge

4) Also there are no back up lights on the trailer. If I have the truck running while using the winch will the truck system be in danger?

The trucks battery and alternator and the charge wire feed back to the trailer is current limited by the size of the circuit breaker be it a 20 or 30 amp etc

See how the other fine gents do this What I posted is NOT the only way to do this but how Ive done it. THERES MORE THEN ONE OR MY WAY TO SKIN THIS CAT LOL

John T

I just strap a deep cycle battery to my trailer to power my winch, fully charged it will pull something on no problem. I carry 2 sets of jumpers to reach the truck battery In case I run out of juice. I just charge the deep cycle with a trickle charger when It needs it

Just wired up my dump trailer to use the pickup battery.

** You run a 2/0 welding wire from the + terminal on the battery to a 300 amp circuit breaker then to a high amp quick disconnect at the back of the pickup. It around 20 or 25 ft.

** You run a short 2/0 welding wire from the back frame of the pickup to a high amp quick disconnect

** On the trailer side you wire up the other half of the high current disconnect and connect to your winch --- in my case it was a hydraulic pump.

I'd add qty of 2 --- 2/0 x 1/4 cable ends as they would work better with the 300 amp circuit breaker.



Parts list

- ANJOSHI 300Amp Circuit Breaker
- micrl 2/0 AWG 350A Battery Quick Connect/Disconnect, Jumper Cable Plug Connector Kit for Recovery Winch
- TKDMR 10pcs 2/0 AWG-3/8 Battery Lugs,Copper Wire Lugs,Heavy Duty Battery Cable Ends
- SELTERM 2/0 AWG 5/16 Stud (5 pcs.) UL Heavy Duty Battery Ring Terminal 00 Gauge Connector,
- 2/0 Welding Cable --- have to measure what you need -- I used 40ft

The basics have been covered well. One mistake is the use of a deep cycle type battery. The discharge cycle for deep cycle is suitable for running lights, fans(not AC), radio, etc. The amp draw for a winch on trailer or truck is rapid and very high amperage. This is the exact opposite of the design of deep cycle, which have many thin plates, very close together. The deep cycle plates will heat rapidly, and begin to warp under high amp load conditions like a winch motor draws.

Use a good condition starting battery, group 35 or equivalent. Rapid, heavy current use on a deep cycle battery will eventually warp plates, and cause a shorted cell. It is an incorrect application for winch or other high draw applications.

Some food for thought.

How often do you use the trailer? How often will you actually use the winch? Do you haul a lot of "dead" tractors and equipment?

Mounting the winch itself is a good idea, protect it from the weather and road spray.

As for the battery. How often will you actually use the winch? Daily, twice a week, every other week, or maybe once a month for example? The thing is it may be more practical to have a set up that allows quick and easy installation and removal of the battery. It does a battery no good to bounce around on a trailer when it is not needed. You can keep the battery on a maintainer in the shop when not needed, install it when you think you will need the winch. We have loaded 2 yard loaders with a 9000 lb. winch powered by a group 24 battery. The battery didn't need a boost or charge during the process. Also proper use of snatch blocks to multipart the winch line will keep the power draw lower than using a single line pull.

If, you use the winch almost daily, I could see mounting the battery and setting it up so it charges from the truck. Once a week or less, I'd put a battery on when needed.

The option of running heavy cables, from the truck battery, to the rear of the truck with matching connectors on them and the winch power cables is another way that has merit. You could make the winch cables (long enough to reach the truck battery) with booster cable clamps on them and just hook them up when using the winch. And using the truck eliminates one battery.

I'm not saying what you want to do is wrong, I'm just throwing out some things to consider.