[jelag]

You are describing a bad ground, but I think its in the trailer and not the truck... I'd suggest you open one of your tail/stop lights and run a test jumper from the ground wire in that light to the truck... I'd just use a small vice grip to clamp the wire for testing to the connectors... I don't think your 4-5 ohms is out of line for a ground circuit... but remember your not testing the bad connection... With the tail light open you might also try the ohm test from the ground in the tail light to the truck... REMEMBER not to have the circuit powered at this time...

We've had problems with trailers as well... We've run an 8 gauge wire from the trucks (12+) battery to the trailer plug through a 40 amp fuse... We also ran the same gauge wire from the trailer plug to ground...

We've also ran the same size wire in the trailers....

We've found that the trailer batteries charge faster, and hold a higher voltage.. on one of our work trailers we've installed a relays to run both stop/tail/running lights instead of the factory wiring... using the factory wiring to trigger the relays.. and drawing power from the 12+ lead in the trailer battery box..

One last thought... when we get the time we remove all the scotch lok connectors and use a good butt connector and shrink tube.. the shrink tube we use has an adhesive that is heat activated so the connection becomes water tight...