I headed across town today to give my mom a Mother's Day card and my 78 T140 just quit as I approached a stop sign. It started right back up but then happened again and got worse and worse after a few miles. It was like the key was suddenly switched off. I eventually realized that it would run fine if I left the headlight off. By the time I got back home the headlight would kill it as if it were a kill switch. Battery is a 3 year old Carquest China special. It shows 12.2 volts and the horn sounds pretty normal. I built my own air cleaners since I live on a dirt road and the originals seemed to seal poorly so I mounted the zener on a frame gusset- was that bad? It is normally cool where I live so I didn't give heat issues much thought. What have I done? Or could a lame battery make it act like that?