I haven't looked at one of the units you have - but if the trigger and "controller" (transistor package) are built into a single unit - and then captured inside the distributor body.......... the unit has to have a secure body ground wire (to the block) - and the controller has to be transferring heat out of the electronics as well as grounding it to the body. On a GM HEI unit - carried inside the distributor - the unit has to be clamped down with "couplant" (heat transfer paste) - a dry surface beneath one is trouble. Most of these gadgets have a protective "interrupter" circuit to prevent overtemp from destroying the electronics. When it cools down - they turn back on. Sounds like what is happening to yours.

I haven't looked up the Accell #8140 - but you are interested in the OHMs of internal resistance they report. The 42K volts is the dielectric resistance of the wire in the coil - not the output of the unit.
Later: looked up the #8140 coil - primary OHMs are shown as 1.4
only diagram I could find for this set-up



 
 Steve Metzger       Tucson, Arizona

Right now  the ground is to the fire wall, I'll move it to the block and see what happens.
The funny part of this equation is that for last 3 years and 8 months the ground has been to the fire wall with no problems. Last summer drove to Detroit and back with no problems. All the problems started this summer.....WHY??????
Thanks again,
Tim
Wet, Florida
33706

The illustration I found shows a key switch to the coil power - don't. On the systems I've built, I used a power relay for the heavy lead to the coil - and left that wiring outside the passenger compartment. The key switch fires the relay. A jumper from the starter solenoid will give it power while cranking.
The highest electrical potential on the vehicle (volts) exists between the frame of the generator/alternator and its output lead. Since it is usually bolted to the block - the engine block is the next best ground available. 

Ford had service problems with the old Duraspark II ignitions of the seventies - the distributor ground was wired back to the controller box on the fender liner. Adding a wire from the block to the distributor body made many gremlins go away. There were other troubles - but this one was easy..... 

 
 Steve Metzger       Tucson, Arizona

Steve,
Correct, the + coil wire is connected to the ignition switch. We can change that.
Want to let you know that I've added a ground to the block and left the fire wall ground in place ( u  can never have too many grounds)
Will send you an update.
Big thanks,
Tiny Tim
Fl 33706

If you can live with an E-core coil - consider switching to one. They are built with high temp wire to accommodate the HEI type of electronics. The design is configured to maximize the amount of amps fed into the coil - and that means plenty of heat. The old oil filled cylindrical coils just can't deal with the heat so they must have a ballast resistor to deal with the current.

The term "E-core" refers to the shape of the steel armature plates upon which the coil wire is wound. The Ford "TFI" ignition used an E-core coil that is easy to come by at the yunk yard along with a mounting bracket and an adaptable snap-on connector for wiring. They are about 1.2 OHMs primary resistance and high temp resistant.
 




 
 Steve Metzger       Tucson, Arizona

Steve,
Had an e-coil like that on my last car, never had any problems,
In the mean time, would a ballast resistor help to keep the new Accel coil cooler ?
What do you think ?
Tim in Florida

The resistor will help lower the coil temp - but it will be getting hot too. The design of the HEI chip is to dump amps and the resistor will be taking some of it. I tried a heavy duty Mallory resistor on one of my systems and it "died" at an early age. Why not just get a low resistance high amp, heat resistant coil and run it?

The energy eaten by the resistor doesn't go to the plug - and the energy stored in the coil fires it. So performance of the spark producing system is reduced as the total resistance rises.

Here are the coil energy traces of a low resistance coil and a higher one. The area "under the curve" is indicative of the stored energy that goes into the spark......




 
 Steve Metzger       Tucson, Arizona

Steve,
Going to order the external ignition coil. I've also ordered an other new HEI distributor.
When they are all here, I install and let you know.
Again,
Big Thanks,
Tim
Florida 33706

Tim - it occurs to me that a "mystery" I encountered might be tripping you. The start position of my t-bird dash switch did not result in power to the coil. In "run" all was well - but turning to "start" the coil was being powered by a jumper from the solenoid on the firewall. So a quick spin of the engine and releasing the key would (sometimes) make the engine "catch" and run. But this wasn't consistent. The wiring diagram I sent earlier doesn't necessarily show this Ford type of switch - instead maybe a GM version where "start" also powers the coil. On the t-bird this "jumper" from the solenoid also entered the circuit in such a way as to eliminate the resistor and directly energize the coil - an extra energy burst that would not damage the old oil filled coil.

You could check for this by lifting the heavy lead down to the starter motor and looking for coil power with a meter - when turning the switch to "start"..

 
 Steve Metzger       Tucson, Arizona

Steve,
Will do that test and advise.
Thanks,
Tim
Florida