Can't get the lights on camper to work when I turn on a signal light both tail lights on camper flash thats the only lights that work . I drive a 2004 silverado

check for camper wiring and trailer plug connections

First thing to check is make sure the 7-way is plugged in firmly. Many times after connecting some people might accidentally trip or pull on the electrical connection. Next would be to get a test light and with your vehicle lights on start checking each of the 7 contacts in the 7-way right off the rear of your truck to make sure your 7-way was installed/wired correctly. If you still have the package for the 7-way that you installed it should show a diagram illustrating what contact is for the running lights and tail lights. If your test light pops on for each of those contacts then you have either bad bulbs or bad wiring on the trailer.

Check the relay fuss near the fuss box, also check the fuss itself. If this will not work check your wiring harness and lead wiring lines that feeds the tail lights. If the tail lights work along with the brake lights its not a wiring issue its either the fuss or the signaling arm drive relay box on the steering. Also check your 4 way fuse as well

Check the ground On the camper

When you disconnect the battery it resets the ECU (computer). These have a lot of computer problems. Still working normally? Please rate.

Pull the steering wheel and clean the turn signal switch and look for broken parts. If that doesn't fix it, then replace the turn signal wand on the steering column.

I'm inclined to believe it is the turn signal switch. When you select left or right, the brake light is removed from that side, and the flasher is connected to the bulb instead, making the brake light on that side flash as the indication that you plan to turn. You have lost everything, but the simple answers check out.

If you have lost signals, brake lights and tail lights, then it is more likely that the ground supplied to the bulbs is not working, since the tail lights share noting in common with the brakes lights and turn signals but ground.

If the tail lights work, the fact that the brake lights and rear turn signals share that switch starts to look meaningful — even more so if the front turn signals also don't work. But the front signals and the rear signals use different circuitry in the switch, so it would be something more mechanical in the switch than electrical in that case.

Sounds like you need to replace the drivers brake/tail light.

Check the taillamp fuse on the truck. If it is blown, you either have a short in the wiring of the camper, or the 7 pin inverter box on the camper.