So i wanted some back up lights on my car trailer that come on when i put the truck in reverse so i got to rubber tractor/utility lights from TS and mounted them on the back of the trailer fenders. I then ran a wire back from the center pin of the 7 pin connector on the trailer to the lights. When I put the truck in reverse it poped the fuse for the reverse lights. I then replaced the fuse and disconnected the additional reverse lights i had mounted on the truck. The lights work but they are very dim. So i am wondering if there is some sort of relay i can get so the reverse lights on the trailer feed off the trailer battery and the power comming from the truck when it's in reverse is simply a signal to turn them off/on. Let me know your thoughts on this.

A few questions and comments first so I'm sure I understand what's goin on.

First off the lights your hookin up as backup lights are probably illegal. They have to be a diffused white lens under a certain wattage and if you bought off road tractor lights they probably don't meet either requirement.

Don't know what you have for trailer lights but backup lights are the same thing as brake lights with a white lens. If you go this route you can run them just like you originally had them and they will work fine. Just using the auxiliary pin for juice.

You can use the lights you have but they will have to work from a switch and not your backup lights. First time a cop see's ya on public property when those offroad lights come on your busted, no different then runnin the off road lights on the front of your truck while your on road.

The trailer just passed Pa state inspection and my mechanic said the lights were fine how i had them. Thats the reason I ran them off the center pin so they only come on when in reverse. I just want a way to get more power to them so they are brighter and actually worth a shit when backing up.

yeah you could put a relay there if you have a battery in the trl, then it would act like a starting solnoid, battery would power the light and the solnoid turns it on and off

I'll quite after this and let ya do what your gonna do but I'd feel guilty if I didn't say somethin. I've titled and plated trailers that I've built myself that at the time of registration didn't have a single light installed, missing fender covers and so on. It's unfortunate but they really don't pay any attention to trailers. They'll pass anything, they leave it up to law enforcement to for the real inspection. But anyway, spent some years in the trailer business and anything brighter then your brake lights back there is considered "Axillary Off-road Lighting" and is covered in the laws. Here's the excerpt right out of Pennsylvania's rule book on the matter.

(f) Off-road lighting.--Off-road lighting lamps may be mounted on the roof or roll bar of a vehicle and shall be covered with an opaque covering that prohibits any light from being emitted when the vehicle is being operated on a highway or trafficway. Any person who illuminates an off-road lighting lamp while the vehicle is being operated on a highway or a trafficway commits a summary offense and shall, upon conviction, be sentenced to pay a fine of $100.

Ok i dont know how things work in illinois and i dont know why you register a trailer that was missing lights or fenders but shit like that dont fly in Pa. Also the mechanic I deal with for state inspections has run his own shop for 30 years and regardless of what he's inspecting (boat, car, RV, motorcycle ect.) it's by the book.
I just want to know what kind of relay I need or how to get more power to the lights, not a lecture on whether or not they're legal.

i was looking in the aw direct book last night for back up lights for my new inclosed trailer and i found a set of LED brake and turn rectangler lights that is outlined with clear for back up lights. didnt fine them on line but just go to there web site and at the top request a catalog

The wiring hangin off the back of your truck provides plenty of power to run an RV camper full of lights, appliances and anything else you want to plug in. With that in mind, your two little lights if wired correctly will work just fine off the plug. The mechanic that did the inspection didn't tell you how to make these work.

We come here to exchange ideas and thoughts and to have conversations about things. If all you want is an direct answer to your direct question then you probably need to go find a book with a schematic in it. Sorry to have wasted your time with my idle chat.

Might want to check the grounds on the trailer and make sure the connectors are clean and shiny in the plug itself. A little dielectric grease goes a long way on trailer plugs.