I was removing the old 4pin wiring harness and wiring a new one, I have done several of these and never had a problem. I removed the one that was on there because it was cracked and falling apart, and the wiring was messed up. Everything as far as the regular lighting with the taillights,turnsignals, reverse, and brake lights worked fine. I wired in the new one and everything was working correct, because I hooked up the 4 pin plug to the "line of fire and ice" LED stick and it all worked as well as the taillights as usual. Then I taped up the wiring underneath and checked the lighting again and the taillights were dead. but the light stick was working? I don't know what happened so I disconnected the 4 pin harness and was left with the factory wiring and still no taillights, both taillights flash with the right or left turn signal, no reverse lights, the brake lights light up and when the turn signals are on they are very slow? I checked both brake/tail light bulbs and they were fine. I checked both rear bulbs lots of yellow putty/wax junk inside (I believe was to keep from corroding) both bulbs looked fine but the one came loose from the metal base and the glass was just turning, I replaced that bulb but still acting up. Like I said I have done several of these never had a problem but now last night after it was all working properly it started acting up. Can I check the bulb sockets with a multimeter for a certain amt of voltage at the bulb sockets or maby the light switch, I think something is messed up as far as a bad ground because with the headlights off the brake lights work but both turnsignals light up at the same time almost like 4 ways. If this truck didn't have the 300i6 in it it probably would have been gone, but she only has 90k miles on her. I am thinking it is just something simple but I just have to find out what. When lights are off turnsignals light very dim in the rear and light up as the front ones are going dim,(flash opposite) 4ways work with out parking/head lights but flash opposite, front and back. When I turn the lights on the taillights are dead. When I turn the key on to test turnsignals the running lights are on in the rear even with the headlight/parking lights off. No reverse lights at all. Does anyone happen to know where the lights are grounded at so I can check for a bad ground?