trailer Wiring on 2003 PreRunner w/Tow pkg

I've got a 2003 PreRunner with the towing package that I bought used. It came with a flat 4-pin trailer connector. I recently bought a used enclosed trailer with a 7-pin connector. I wired up a flat 4-pin to round 7-pin adapter that worked great. I had tail lights, brake lights, and turn signals working on both truck and trailer. On a recent trip, a couple of wires in the adaptor worked loose and shorted, blowing the turn signal fuse. I replaced the fuse , and reconnected the wires in the adapter, but I now have tail lights only - no brakes or turn signals. The brake/turn signals work fine on the truck, but nothing on the trailer. I checked out the adapter and it is wired correctly. I ran 12Vdc directly to the round trailer plug and the brake/turn signal bulbs work fine. I checked the voltage at the flat 4-pin on the truck, and there is a signal there for both brakes and turn signals, but it is only about 7 volts now - not enough to light the brakes/turn signal bulbs. Any idea what has happened? Why would the voltage from the truck 4-pin be low now? Thanks for any help!!!