One Leg Ballast Resistor or Two

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mopardude62

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I have a 1967 Barracuda with a 273. I'm converting to Electronic Ignition and have the Mopar Performance kit sitting right in front of me. Since my wiring is pretty dry and brittle, I figured a new wiring harness was in order.

Back in October I ordered an original harness for my car modified for Electronic Ignition. It arrived today and I noticed it had the connectors on it for the dual ballast resistor.

I have the single ballast resistor in my kit. I'd like to stay with the single ballast because I want to keep it in the stock mounting location. It currently mounts in a little spot over the left inner fender back against the firewall and I don't think I could stick a dual ballast in that spot. Also, since my MP EI kit came with a single ballast, I know it will not use the red/green wire on pin 5.

What do I need to do so that I can use the single ballast resistor?
 
Whether you CAN or MUST use a 2 or 4 pin ballast depends on the ECU you have.

However, if this is a new kit, I would assume it is a 4 pin ECU

A 4 pin ECU CAN use EITHER a 2 or 4 pin ballast

A 5 pin (older) ECU MUST use a 4 terminal ballast.

Unless you have a stash of older ECU's lying around, I would wire it up for 2. You an either cut out the other connections, or just leave them and connect to the 2 pin resistor.

You can NOT tell a 4 from 5 pin ECU by looking, because some of the 4 pin ECUs have 5 physical pins. You can only tell for sure by using an ohmeter from the 5th pin to some of the others.

Wiring difference:

4 pin ECU/ 2 pin ballast

Ignition_System_4pin.jpg


5 pin ECU/ 4 pin ballast

Ignition_System_5pin.jpg
 
Please forgive my third-grade artistry but here's what I want to do. I have what is in the top half of this picture and want to go to the single resistor shown in the bottom half of the drawing.

I think all I need to do is connect both blue wires together to form one terminal of my single ballast connector. Then I can simply cut the red/green wire out of my harness and use the blue/brown connector for the other terminal.
 

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When I did one of my cars, I wired for the 5 pin ECU (dual ballast resistor)

I did this so that I didnt have to worry about which ECU I put in there, 4 or 5 pin either will work but yes I realize it is one more thing that CAN go wrong but it's minor and easily testable.
 
There's an error in my drawing. I have the blue wire coming out of the bottom of my connectors labeled "Blue to Distributor" it should be labeled "Blue to Coil"
 
I've been thinking about this and I'm going to take the advice of the Kernel and just install the dual ballast resistor. It's the easiest thing to do, no cutting and splicing of wires which is why I wanted a new harness in the first place. I'll post some pictures when I'm done!

Thanks Kernel and 273Dart for your advice and replying to my inquiry!
 
Don't go by wire colors, unless you can post the diagram it refers to

But look at the 4 pin ballast in the diagram I posted. NOTICE the notch in one end? This is IMPORTANT. It places the ballast in the proper orientation, because the two resistors inside the 4 pin ballast are DIFFERENT from each other. Therefore if you turn the ballast around in the diagram the incorrect resistances be in the circuit.

Notice that in reality, all you are doing with the 4 pin ballast is adding one more wire to the ECU
 
mopardude62,

It looks like your plan will work fine. Your bottom drawing shows single terminals in place of your current dual. If true, you don't have to cut/splice wires. You should be able to release the "57 terminal" female connectors from your dual pin housings using a tiny screwdriver and re-insert them in single pin housings (your old ones, junk yard, or ebay). I wouldn't remove the green/red wire, but just leave it in the harness. It won't be connected at either end.

As a probably unwelcome rant, I wonder why people fool with the old Mopar electronic ignition and pay $$ for new MP parts and $$$ for new harnesses designed for it. A GM HEI ignition is easy to retrofit, gets rid of the ballast, and lets you use a better E-core coil. I put them together for several of my cars for ~$20 in junkyard parts, as have others. As you are finding, new high-dollar stuff is not always "plug and play".
 
. A GM HEI ignition is easy to retrofit,.

It's what I use. "Saw them" on the www and used it first in my Toy 20R powered Cletrac. My 67 runs an Accel "look alike" Mopar breakerless dist and an HEI module.
 
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