Not getting 12v to coil on start ('73 Dodge W200 360La)

[Eddy Hoover]

Hello good buddies,

Main issue on my dd: not getting 12v to coil when running ign hot lead is attached to ballast

Testing: I have 12.5v at battery, starter cranks beautifully, 12.5v coming out of both leads of ignition switch and firewall, 12.5v on start at ballast when run wire is not connected. When run wire is connected to ballast, start wire=11v.

Back ground: I have a 4 pin ballast, originally a real 5 pin ECU (not points), and an msd ign/coil setup, triggered by the original coil positive wire. In my hast to use the timing light, I redid the wiring (to make it easy to switch between stock and Msd ignition) and left the msd coil connected to the stock system. Inevitably the blaser 2 coil burned out the 5 point ecu and was replaced with a new 4 pin ecu. With stock system in place (stock coil as well), car will only start if I quickly flip the ignition switch from start to run. Hence the msd box, which is tested and good, is not triggered by the old wire for +coil. Tried spare ballast, ecu, and voltage regulator and looked for shorts, but no dice.

Everything runs if I momentarily connect a battery hot lead to +coil in stock system or trigger for msd box.

 

[Mattax]

There never should be 12 Volts at the coil.
On a standard (kettering) system like the factory ecu or points, the voltage in Start is battery voltage - which should be higher than 9 Volts when the starter is turning, but rarely as high as 12 Volts.
With the key in run, the voltage will vary from system voltage (points open) to something less than that as the current flows through the 1/2 ohm resistor (points closed).

With a capacitive discharge system, power goes to the coil primary circuit when the capacitor in the CD box discharges. The coil than transforms that pulse into high voltage pulse to the spark plugs.

 

[67Dart273]

Sounds like you mis wired something in the conversion back and forth

The basics.

When IGN sw is in "run" the IGN1 / run wire feeds 12 v to one side of the dual ballast. That end has both terminals jumpered together. Through the ballast we go, to the coil, and to ground through the ECU box which DRAWS CURRENT ANYTIME the key is in "run." (Current flow is actually backwards, neg to pos) The current through that circuit causes VOLTAGE DROP through the resistor, so the coil DOES NOT see 12v. Rather, engine off, key on, coil + should show somewhere between 6-10V. This varies with resistor, with coil type, etc

With key in "start" IGN1/ run GOES DEAD. Starting power is now supplied ONLY by the bypass circuit, often brown, IGN2, goes to the coil + side of the ballast resistor. This circuit feeds "hot" power to the coil and goes BACKWARDS through the coil resistor to feed back power into the ECU to power it during cranking

Coil + should show "same as battery" during cranking, and not below 10V absolute

 

[67Dart273]

I see several possibilities:

1...You disconnected/ left something out with the rewireing
2...There is a poor connection thorugh the bulkhead terminals for the IGN2 wire
3...Either the key switch IGN2 circuit has failed or the switch connector is bad on the IGN2 terminal

IGN2 is hot only in "start" at same time as starter relay "start" wire circuit BUT THEY ARE separate switch contacts. EXCEPT as far as I know some years the IGN2 is derived by using a different starter relay with an added contact, which I've always known as a "Jeep" relay

What they are calling the "fuel pump ballast resistor" at top left is the "new" added terminal

 

[Eddy Hoover]

I see several possibilities:

1...You disconnected/ left something out with the rewireing
2...There is a poor connection thorugh the bulkhead terminals for the IGN2 wire
3...Either the key switch IGN2 circuit has failed or the switch connector is bad on the IGN2 terminal

IGN2 is hot only in "start" at same time as starter relay "start" wire circuit BUT THEY ARE separate switch contacts. EXCEPT as far as I know some years the IGN2 is derived by using a different starter relay with an added contact, which I've always known as a "Jeep" relay

View attachment 1715721289

What they are calling the "fuel pump ballast resistor" at top left is the "new" added terminal

Thank you for the replies, I will give the wiring and starter relay a look

 

[Eddy Hoover]

I ran a wire from the starter side of ballast to the trigger for the msd, worked like a charm. I must have broken the old wire somewhere on the inside when I was changing the connector.

 

[67Dart273]

I ran a wire from the starter side of ballast to the trigger for the msd, worked like a charm. I must have broken the old wire somewhere on the inside when I was changing the connector.

You pulled this off the "start" wire? Be careful that will try and backfeed. The coil circuit will try and engage the start relay in park or neutral, and "draw down" the coil voltage if "NOT" an MSD You might have to put in a series diode in the new wire. About 10A 24 or more PIV to be safe

 

[Eddy Hoover]

You pulled this off the "start" wire? Be careful that will try and backfeed. The coil circuit will try and engage the start relay in park or neutral, and "draw down" the coil voltage if "NOT" an MSD You might have to put in a series diode in the new wire. About 10A 24 or more PIV to be safe

I really appreciate all your help; I have read a ton of these forums and learned a bunch from your hundreds of comments. I've been driving my truck since I was 16 (5 years now!) and although still a novice, I have learned a ton. I messed around with the wiring some more and was able to hook up the stock coil wire to the msd box. I have been dding it for the last few weeks with no problems. There may still be a gremlin in the wiring, but hopefully replacing the altenator wire and bypassing the ballast (since I changed from a real 5 pin ecu to a 4 and was running it through a dual ballast) fixed my problem. And for the future people like me, don't hook a blaster 2 coil directly to a stock ecu, and use a ballast with a stock system.

 

[67Dart273]

Yer welcome