1968 w300 318 would not start. Found that there was inconsistent spark from the distributor. I checked if the points gapping was correct (match pack thickness). Tested and or changed the following: dist wires, dist cap, coil (use with external resistor), and ballast resistor.

Still had the same problem so I installed a new remanufactured distributor and still no luck. I made sure it was the correct dist, correct ballast and correct 12v coil (use with external resistor type) I took out the dist, put it in a vice and hooked up my own system. Goes like this:
-neg on 12v battery to ground dist in vise on bench
-from +ve from 12v battery to ballast resistor
-from ballast resistor to +ve on 12v coil
-from -ve on coil to dist
-of course I have the wire connected from center of coil to center of dist cap and also spark plug wire connected to spark plug tester or I've also used other things to check for spark.

What happens is when I turn the dist shaft with my finger, I will get spark for the first minute then it will be inconsistent or no spark. Also the ballast gets red hot and will smoke within the first few minutes.

 

the parts really cook when the engine isn't running. that's why you shouldn't leave the key in the 'on' position to listen to the radio.

how many miles on this engine? a lot? i was just wondering how the timing chain/gear are, when worn, it can do that.

are you using a same condenser or did the rebuild come with a new one?