Truck won't start

:banghead: I have a 1984 Dodge D150 with the 318 in it. I rewired the tail lights on it and ran the ground wire to the battery after talking to several auto techs in the area. After I ran the ground wire to the negative lead the engine wouldnt turn over but would trun backwards then turn over. After the starter wouldnt turn over, I removed the starter and got a new one after I tested the old starter to make sure it was dead. I hooked up the new starter and the engine will not turn over still. I have the ground for the tail lights unhooked and it still not turn over, there is 12.7 volts going to the starter but it will still not turn over. I removed the starter and hooked it up to my battery charger and it turns over then but will not trun over on the truck.

Since the problem started after you hooked up the tail lights. Disconnect the wire that caused the problem. If it starts at this time double check your wire something doesn't seem correct. Could possibly have got the ground and positive hooked to the wrong wires.
Almost 95% of the time when something likes this happens it was caused by a simple mistake.

I have already tried that. I talked to someone that works with cars and he told me to check the relay wires. Thanks anyways

check to see if you got a blown fuse
get a voltage tester. you will not fine the problem with out one.
check to see if you have voltage at the start wire at the starter solenoid.
if you do not then trace back to the relay. you will fine alive wire there for sure. if you jumped the two large wires it should start. the small wire will come from your key switch.
if you do not have voltage at al test points you will be looking for a broken wire .some were between point were you have no voltage. if you under stand all of this your problem you should be able to fix..
alan