How to Wire a Truck to Charge Your Camper Battery

If you’re not familiar with truck campers, they are a type of camper that is mounted on the back of a truck. They are very popular because they offer many benefits over traditional camping trailers or RVs.

One problem you may encounter when using your truck camper is that the battery dies while plugged in at an RV park. To fix this, all you need to do is wire your truck to charge your camper battery!

How to Wire a Truck to Charge Camper Battery

Wiring a truck to charge the camper battery is very simple. All you have to do is run a wire from your truck’s battery into the back of your truck camper where you’ll then plug in your camper’s power cord.

This allows the camper battery to get charged by the alternator, keeping it fully charged while plugged in at an RV park or campground.

To start wiring your truck, you need to know which wires on the back of your fuse box are hot when the engine is running.

You can find these easily by turning on your ignition and touching each wire with one lead of a multimeter.

After doing this to each wire, you should have your positive and negative wires.

Once you know the power leads, all you need to do is connect them to a 10 gauge cable (run of the mill household wiring will not be able to handle the loads involved).  

The positive cable connects directly to your small positive post on your truck battery, while the ground can be connected anywhere that metal is exposed without being painted or near any moving parts.

The only requirement is that it’s free of grease.

It is important that if you are running metal conduit through critical areas like under carpeting, that it be properly grounded via grounding clamps.

Also pay attention to polarity when making connections so as not to short out the battery.

With the small positive post on your truck battery connected to one end of your 10 gauge wire, you can connect your ground to the other end. From there, just run it through an exterior wall of your camper and into where your power cord is stored.

Once all of these steps are completed, you’re ready for that nice charge while plugged in at an RV park!

What you need to wire a truck to charge your camper battery

• 10 gauge wire
• 2 ring terminals
• 2 butt connectors
• A fuse holder and fuses
• Wire cutters/strippers/crimpers/Solder gun

Steps to Wire a Truck to Charge Your Camper Battery

Now that you have everything you need (listed above), follow these steps to get your truck ready for 5th wheel camping.   

Find positive and negative power leads

Find the positive and negative power leads on your fuse box in the back of your truck; these are usually located behind each individual circuit break (there should be small metal pins sticking out of them).  On most trucks these will be red and black wires.   

Note – sometimes even though there is power at this terminal it will be hot when the ignition is off.  If this is the case you will need to tap into the wire behind the fuse box.

Take care of the wires

Cut your 10 gauge wire in half, giving you 2 sections of 5 feet.  Then strip each end exposing about 3/4 inch of bare wire.  Next, crimp on two ring terminals to each end.  

Take the positive ring terminal and insert onto the fuse holder

Take one positive ring terminal and insert it onto one side of your fuse holder (this should just slide in).  Take your other ring terminal and crimp it around the positive post on your truck battery (red or black).   

Crimp the two ring terminals to each end

Strip each end of both pieces of ground cable, exposing about/4 inches of bare wire, then crimp on two ring terminals to each end.  Now, take one of your ground ring terminals and attach it to the negative post on your truck battery (this is usually just a bolt that you can place a wrench or socket onto and tighten it down).

Slide into the slot between the two fuses

Now that the positive and ground leads are connected to the fuse holder, you can slide it into its slot located in between any two fuses (make sure not to block any of the existing fuses with it; also see note below about what I found out about where/how I wanted my fuse holder located).

Connect each piece of ground cable to each other

Once this is complete, all you need to do is connect one end of each piece of ground cable from step 4 to each other, and the other end to an exposed piece of metal on your camper. 

Your positive lead should be connected directly to your small positive post on your truck battery, while the ground can be connected anywhere that metal is exposed on the outside of your camper without being painted or near any moving parts.  The only requirement is that it’s free of grease.

Plug in at a campground

If you are running metal conduit through critical areas like under carpeting, make sure to use proper grounding clamps for both ends of this wire so as not to short out the battery.

With all connections made, all you have left is to plug in at a campground!  

Note – I had no idea where I wanted my fuse holder to go, so I chose the only spot that was open.  After looking at it for a few minutes and fooling around with all my cables, it occured to me that there already was a spare fuse holder sitting under all the other fuses (this took 10 minutes to notice). 

 It turns out that if you look up under the lip where the cover closes over your fuse box there’s actually 2 fuse holders; one built into this little rectangle and another thrown in as an afterthought (basically just hanging off of some wires).  So, do yourself a favor and choose either of these spots instead of having to make room on top of your existing fuses like I did.

Safety Precautions

• Always make sure your camper batteries are fully charged before you leave.  Make sure you have some way to charge them while on the road so you don’t drain your truck battery.  This is why I just chose not to work with my truck battery at all, which is probably better for it anyways.

I always keep a power inverter in the back of my truck that’s plugged into my cigarette lighter socket that can provide 110v AC power for anything I choose to plug into it (like a charger).

• If you plan on working with your truck battery directly, be careful not to short or drop too much voltage across it either by accident or according to design.  Shorting out the ignition switch with a screwdriver while starting your truck might not have been the safest thing ever.
• Make sure you have some kind of fuse or circuit breaker in between each component that could be potentially damaged by too high voltage, shorting out, etc.  The last thing you want is to blow up your camper batteries when trying to charge them from your truck battery or blow a fuse in your inverter or something else when trying to charge it from a generator.
• Check all electrical connections every so often for corrosion and clean/tighten as needed.   

Note: A few days later I decided my ground cable connection wasn’t quite solid enough so I soldered it directly onto an exposed bolt on the frame of the camper where it hooked up to the ground.  This was a lot better and should be good for a long time.

Troubleshooting Tips

• If you can’t seem to get a full 12 volts into your camper battery from the truck, try measuring the voltage out of your truck battery first.  It might be that it’s just not able to provide enough power for whatever reason (low charge, short in the electrical system, defective alternator/generator/etc). 

Next, borrow a friend’s car and hook up their alternator temporarily.  If you can get well over 12 volts out of this charging source then your problem is likely to be with the truck battery or its wiring rather than anything else.

• The same goes for getting an adequate charge coming back from the camper batteries and into the truck.  I’ve got 300 watts of solar panels and a small inverter, so if I camp where there’s no hookups available (free camping) I can get by with charging my batteries off of AC power once in a while and giving the truck battery a boost every day or two.  

If you’re powering an electric fan or something like that then this might work for you, but remember the standard formula: Watts / Volts = Amps; meaning that your current draw will be the number of amps times 12 volts (or whatever voltage your camper is set at).

1. If you’re having trouble getting adequate charge going to your camper from your generator, double check all connections.  Make sure your cables are properly stripped and have good crimps/connections.  Do this for both ends of the cable and hook up points.
2. Also, double check your wattage ratings on your inverter and solar panels because these might be too low to charge enough under certain conditions. For example, my 300 watts isn’t quite enough to charge all four batteries at once during midday in full sun if I’m not plugged into AC power anywhere (which is usually the case).

Bottom Line

The truck-to-camper battery wiring diagram below will help you determine the best way to wire your camper’s 12 volt system. You’ll have an easier time finding, or making a cord that is compatible with both systems too.

If you’re still not sure how to go about it, don’t hesitate to contact us for help! We are always happy to answer any of your questions and would love nothing more than helping you create your own off-grid dream life on wheels.