On the pos. side of the coil with ing key on run pos. I get only 4.7 volts. I have electronic ignition on my 65 dodge truck. Its not enough to run on the run pos of key but will run on start pos. and will run if I bypass the balast resitstor. I have tried 3 different ballast resistors, no luck. sitll wont run on run circuit. I have swapped coil, ECU, ballest resitstor, distributor, and put a new ignition switch in. I know I should get 6-8 volts on run circuit, why only 4.7?? Its not enough to keep my truck running. If I bypass balast resistor with a wire, runs great. I am buying auto zone, advanced auto, ballast resitors. Should I get a mopar perf. one?? Any other place you would look for a problem??

Fish

with a jumper wire with alligator clips on each end jump from the batt positive post to the upstream side of the ballast & see if that gives you enough voltage. If good then check voltage drops when it's idling from the batt positive post to the starter relay to the firewall bulkhead to the ign switch then out to the bulkhead then to the coil positive terminal for the poor connection that is reducing your voltage. The bulkhead is a common culprit. If the jumper wire does not fix it holler back. EDIT is this a 4 pin ECU/2 terminal "single" ballast system?

Yes, its a 4 pin ECU with single ballast resistor. The bulkhead connector is out of the picture as I direct wired a 10 gauge straight from battery to Alt. I totally have the amp guage bypassed and Im running a volt guage now. I ran this electronic ignition conversion all last year with NO problems at all. All of a sudden, this happens. At least Ive pinpointed to the run circuit. Its prob. a wire thats going bad. I will test as you said above and let you know what happens.

Fish

Before you throw anymore parts at it, what's the voltage going to the ballast? It should be within a tenth or two of battery voltage. If it isn't you need to fix that.

What is the resistance of the ballast? Also check the voltage to the ballast or jumper direct from batt positive to the ballast to see if makes any difference

Start side of ballast was getting just under 12 volts, which is correct. I swapped distributers and that fixed problem. The rebuilt distributer I was using had a air gap that was not parellel, it was at an angle and I coulnt get it a true 8thous from top to bottom, The pick up in the dist may also have been faulty, dont know. with a mopar perf recurved dist. i pulled out of my cuda it fired up and ran for an hour no prob. Voltage at the run side of ballast is now 5.5 volts, still seems low but its running good. Anyone else have under 6 volts going to the coil from the ballast?? Im using a 1 ohm mopar perf ballast resitor.

The ballast will have higher ohms as it gets hotter and less ohms as it cools off. The hotter the ballast is the higher ohms it will have and the cooler it is the less ohms it has. Just curious as to how long the key was on without the eng running when you check the volts at the coil pos terminal ? I only ask because if its on a minute or two the ballast will start heating up and as it gets hot it will increase its resistance some. In other words as the car idles a bit the ballast wont heat up as much with the key on eng not running because the ECU is breaking the coil primary winding everytime it needs to fire a plug so at idle it wont have the current flowing thru the primary circuit which includes the ballast as long as if the key is on powering the primary coil circuit as long as it does without the eng running. That way when you are running the car harder at higher rpm's the coil and ballast cools more since the eng is running faster and the primary circuit is grounded even less time then at low rpm's and when ever the coil primary circuit is open (not grounded coil firing) it is cooling the ballast. And the cooler the ballast the less ohms it will have which will give the coil more output voltage avalible at higher rpm's. So the ballast might be .5 ohms with the car off and key off. Then with the key on for 2 minutes and eng not running it may read .8 ohms and then when running at high rpm's it may read around .5 again. Just a thought but I have see voltage from 5 to 8 volts on the coil primary + side with the key on and all ran fine. Ronb