Riddle me this, Mopar electrical experts.......
To further expand on this post, pay attention to the 4 terminal ballast.
First, you MUST use a 4 terminal ballast with the older, 5 pin ECU
You MAY use a newer 4 pin ECU with EITHER a 2 or 4 pin ballast
You CAN NOT tell a 4 or 5 pin ECU by looking, sometimes. Some 4 pin ECUs are actually 4 pin, but some have 5 physical pins. You must use an ohmeter to determine if the 5th pin is actually hooked up
PAY ATTENTION to the 4 pin ballast. You'll notice that it has an OPEN NOTCH at one end. Refer to your wiring diagrams and you will find this notch illustrated. The two resistors in the assembly are different resistances, I think one side is about 5 ohms, and the other is 1.5?
Referring to the two '73 diagrams I posted, look at them and follow the "dark blue" which goes to regulator IGN, alternator field, and the ignition resistor. This is the switched 12V "run" IGN buss coming through the bulkhead from the key. You need to probe this key in "run" but engine off, and be sure it is close to same as battery voltage. If not you have voltage drop in the ignition harness, probably the bulkhead connector or ignition switch or connector.
Here's how Mopar ignition start / run works
You have three separate circuits, IE several SEPARATE switches inside the ignition switch
ONE is the "run" circuit, in the diagrams I posted the "dark blue" and are hot ONLY with the key in "run." It is NOT hot in "start" or "accessory,"
TWO is the YELLOW which goes to the start relay. This activates the start relay in "start" IF the second push on terminal of the relay is grounded. On older "stick" cars this terminal is not there, is soldered to the relay case, and on those the relay case MUST be grounded
On cars with two relay "push on" terminals----on auto cars the second terminal goes down to the transmission neutral safety switch and must see a ground in park or neutral. ON "stick" cars with a clutch safety switch, that terminal sees a ground when the clutch pedal is depressed
THREE is the brown coil resistor bypass circuit. In the posted diagram for 73 this is shown as BROWN. It comes from yet another separate switch on the IGN switch and only goes one place---from the switch, through the bulkhead and electrically to the coil +, and this wire is hot ONLY in start.
So when cranking, you should have "same as battery" in "start." If much different, say down 1/2 volt or more, you have voltage drop in that circuit. Your number one suspect is the bulkhead connector, no2 is the IGN switch or connector.
You sound to me like you can do this, if you stay with it. Even though I'm familiar with these cars, it helps me to draw out a rendering of the bulkhead connector just as I'm looking at it from the firewall inside and out, label it with the factory markings, and label where stuff goes.
There is no reason you can't adapt a different year harness with a little work. As I posted above, the "MAD" link is good reading, it gives you a great perspective on the problems these cars develop in the bulkhead connector.
Simplified wiring using a 4 terminal ballast. Again, you can use either an older 5 pin or newer 4 pin ECU NOTICE the position of the notch in the drawing of the ballast
Wiring diagram ONLY for a newer 4 pin ECU and 2 terminal ballast
To further expand on this post, pay attention to the 4 terminal ballast.
First, you MUST use a 4 terminal ballast with the older, 5 pin ECU
You MAY use a newer 4 pin ECU with EITHER a 2 or 4 pin ballast
You CAN NOT tell a 4 or 5 pin ECU by looking, sometimes. Some 4 pin ECUs are actually 4 pin, but some have 5 physical pins. You must use an ohmeter to determine if the 5th pin is actually hooked up
PAY ATTENTION to the 4 pin ballast. You'll notice that it has an OPEN NOTCH at one end. Refer to your wiring diagrams and you will find this notch illustrated. The two resistors in the assembly are different resistances, I think one side is about 5 ohms, and the other is 1.5?
Referring to the two '73 diagrams I posted, look at them and follow the "dark blue" which goes to regulator IGN, alternator field, and the ignition resistor. This is the switched 12V "run" IGN buss coming through the bulkhead from the key. You need to probe this key in "run" but engine off, and be sure it is close to same as battery voltage. If not you have voltage drop in the ignition harness, probably the bulkhead connector or ignition switch or connector.
Here's how Mopar ignition start / run works
You have three separate circuits, IE several SEPARATE switches inside the ignition switch
ONE is the "run" circuit, in the diagrams I posted the "dark blue" and are hot ONLY with the key in "run." It is NOT hot in "start" or "accessory,"
TWO is the YELLOW which goes to the start relay. This activates the start relay in "start" IF the second push on terminal of the relay is grounded. On older "stick" cars this terminal is not there, is soldered to the relay case, and on those the relay case MUST be grounded
On cars with two relay "push on" terminals----on auto cars the second terminal goes down to the transmission neutral safety switch and must see a ground in park or neutral. ON "stick" cars with a clutch safety switch, that terminal sees a ground when the clutch pedal is depressed
THREE is the brown coil resistor bypass circuit. In the posted diagram for 73 this is shown as BROWN. It comes from yet another separate switch on the IGN switch and only goes one place---from the switch, through the bulkhead and electrically to the coil +, and this wire is hot ONLY in start.
So when cranking, you should have "same as battery" in "start." If much different, say down 1/2 volt or more, you have voltage drop in that circuit. Your number one suspect is the bulkhead connector, no2 is the IGN switch or connector.
You sound to me like you can do this, if you stay with it. Even though I'm familiar with these cars, it helps me to draw out a rendering of the bulkhead connector just as I'm looking at it from the firewall inside and out, label it with the factory markings, and label where stuff goes.
There is no reason you can't adapt a different year harness with a little work. As I posted above, the "MAD" link is good reading, it gives you a great perspective on the problems these cars develop in the bulkhead connector.
Simplified wiring using a 4 terminal ballast. Again, you can use either an older 5 pin or newer 4 pin ECU NOTICE the position of the notch in the drawing of the ballast
Wiring diagram ONLY for a newer 4 pin ECU and 2 terminal ballast
