Just wondering if anyone could help. I would like to be able to turn the dressing room lights on without starting the truck up and my dad tells me that I need to add a fuse to the truck as thats what he had to do to his GMC. Where do I add the fuse?

It ain't quite that easy on a Ford. On a Ford there a whole lot more to it than adding a 40 amp fuse like you do on a Chevrolet or GMC....... I don't have a Ford, so I'm not quite sure what you're suppose to do, other than..."turn the switch on". You could always add a battery and battery box to your trailer... Then you can turn the light on even when the truck is nowhere near!!

As stated the Fords have a relay that disconnects the truck batteries from the trailer when the truck key is in the OFF position. This prevents you from draining the trucks and ending up with a dead battery.

You can remove the relay as mentioned above or add a battery to the trailer. I would personally add the battery, then you can use the lights when you are not hooked up to the truck, such as loading before or cleaning the trailer after you get home. I did this to my 2000 trailer. It cost about a $100 to weld a bracket on the trailer and buy a deep cycle battery.

On my Ford diesel, it's not enough to have the key on, the motor has to be running for the aux relay to be activated. This eliminates the possibility of running the batteries down, when the aux circuit is being used. As Painted Horse has stated, a dedicated trailer battery is the best way to go.

 If you bypassed your relay and left the trailer lights on, you could have a very bad day. What if you're done with camping and when you try to leave, you cannot start your truck? I highly recommend that you consider PH's recommendation.

Gard

There is a thread on this site from about a hundred years ago on how to bypass the relay...  I don't advise it either.

I decided to use some battery operated lights in the sleeping area. My Ryobi rechargeable 18 volt is handy, along with a Coleman flourescent lantern and smaller one that has a magnetic base (hooray for steel trailers!! LOL)

There are also some converter/ chargers that can be used. Check camping stores. I had one that I could use to air up tires that had a storage battery. Could be recharged from the lighter accessory. It was a bigger pain than using the power tool lamps.  

I would also recommend tha you add a battery to your trailer.  I purchased an aluminum tool box from Home Depot and bolted it to the front of my trailer.  I installed a small deep discharge battery and added an inline fuse holder on the + side then ran the wire to the hot wire screw at the trailer terminal block and a ground wire to the ground.  When driving the truck will charge the battery, when stopped the relay shuts off and I run on the battery.  See picture attached.

Turfa

I think that I will probably end up buying a battery and welding a bracket as stated above. Thank you for all of the replys.