PEEEEER-PLEXED

Had car smoke today. Same stock 4g I, sent to Winter Nats. No clue as to why. Was going to switch gear plate and arm to different chassis with better wear marks on pick-ups. Wanted to see if any difference was noticable. So I put chassis on test track held up rear to warm up alittle. Bottem of chassis lite up and smoke came fast. Have tried to find something evident as to why but everything looks normal. I don't remember for sure what the arm measured in ohms. I've got new AW arms from 14 to 16 ohms. Probably was close to 14ohms when sent to race, think thats the 4g stock limit. Checked the ohms on arm last and got 7.4, 6.4, 7.5. WHAT HAPPENED ? a short in the arm ? Never had this happen with a stock arm. And have no clue as to why. Anyone have this happen to a stock arm ? Or maybe know why it would ?
TIA............PC