cudajim
cudajim
I have a 74 Dart, all stock wiring and working well. My question is, what's the purpose of a dual ballast resistor? I know the top one is used to drop voltage and supply the ignition coil but what's the bottom one for?
Dual ballast resistor
- Thread starter cudajim
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remytherat
Well-Known Member
The ecu. There are a bunch of schematics available on here.
cudajim
cudajim
Point me to one. My bottom resistor has a horizontal crack in it, most likely not the proper resistance now but still working.
remytherat
Well-Known Member
Professor Fate
Push the button, Max...
The initial Mopar ECUs were 5 pin units and used a dual ballast resistor. One side of the resistor feeds the coil, the other side feeds the ECU. On later systems, the 5th pin on the ECU was eliminated and a single ballast was used- the function of the dual ballast/5th pin was moved internally in the ECU and was no longer needed.
This is why you can run a 4 pin ECU on a 5 pin/dual ballast system, but not a 5 pin on a single ballast/4 pin system.
Kendog 170
Let the boy go !
Heres the 5 pin diagram. As said ground (Blue arrow)not needed on 4 pin.
cudajim
cudajim
Now it makes sense. I bought a new dual resistor anyway, everything's working. I also bypassed that ridiculous seat belt interlock relay by hooking the 2 yellow wires together.
bee1971
Well-Known Member
Your original dual ballast resistor
Did it have an open back exposing the coil side resistor ?
Test both resistors with an OHM Meter
Your replacement ballast resistor
Test both resistors with an OHM Meter
Did it have an open back exposing the coil side resistor ?
Test both resistors with an OHM Meter
Your replacement ballast resistor
Test both resistors with an OHM Meter
cudajim
cudajim
No need to test the resistance, I bought a new one for less than 10 bucks. The old one was cracked and just fell apart when I unbolted it from the firewall. The schematic above is a good reference though.
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