1973 Plymouth Duster repair and rebuild

OMG I hate soldering on cars. I can not get it to hold. I have pre heated the wires with a lighter, I have used my flux, I have not used flux. I twisted the strands before twisting the 2 wires together, I have tried not twisting the 2 wires till I twist them together. I have event tried my pencil tip as well as my larger flat tip. I can not get the dang solder to flow. And its not like I have a cheap soldering station. I am building a HO train layout and afforded myself the opportunity to purchase a Hi End Weller with digital controls and heat control. For S's and G's, I even gave my basic Ryobi battery operated solder station a shot.

I am about to terminate the 2 wires on a 2 pin water proof automotive plug, and take the other side and horse shoe a chunk of wire on it in case of further use.

I hate soldering on larger gauge wire. I am great with 20 and 22 gauge. No problems soldering 18 gauge feeder wires to HO track. But give me two 14ga wires to butt together, and its a big fail.

:-(