Hot ballast resistor & ICM

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68red440

68red440

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'74 Dart Sport, 225 with factory electronic ignition & ballast resistor. How hot is normal for the ballast resistor? I turn the key to the run position, and feel it warm up within 30 seconds. After a minute it's almost too hot to touch. Grounding issue? I improved the ICM ground to the inner fender and visually checked all other wiring in the engine compartment and re-tightened ground straps.

I just finished putting the head back on (valve job), replaced a cracked exhaust manifold with a new casting, new water pump, and re-installed everything else that bolts on to these parts. I had a hard time starting it until I bypassed the ballast resistor. It fired right away, ran smooth, and then I noticed the hot ICM & resistor after a short drive. All wiring and grounds were re-installed on the engine exactly as it was before.
Thoughts?
 
So hot that you cannot put your hand on it. That's why it has a ceramic body. It's a resistor. That means it holds back electrical current. It's gonna get hot.
 
RustyRatRod said:
So hot that you cannot put your hand on it. That's why it has a ceramic body. It's a resistor. That means it holds back electrical current. It's gonna get hot.
Click to expand...

I was going to say hot enough where if I told you to touch it and you did, I would start laughing.
Nobody ever touches or smells anything I tell them to around here. :D
 
I had one ballast resistor (after market) that did not have the ceramic fill around the resistor wire. It ran very hot. Check yours to see that the resistive wire is not totally exposed in the housing. This ballast would discolor the paint on the firewall where it was mounted.
 
The resistor that's in there now has the ceramic fill and is working, but the last one got so hot that it blew. It sounded like a firecracker went off. The ceramic blew out of it and the wire is exposed. The white paint is now black under the resistor.

Yes, I understand a ceramic resistor is expected to get hot. I plan to drive it 600 miles to Farmington in 3 weeks, and I want to sort out any electrical gremlins.

Per the FSM I checked the voltage and resistance at the 5 pins. I guess I will just clean all grounds, re-check all wiring, and drive it locally with jumper wires on hand in case I blow the resistor again.

The factory ICM also heated up, and the insulating material started melting after a short drive around the neighborhood. I installed a Duralast ICM, but I noticed it is missing Pin #5 which is the ground. Not sure I want to use it.
 
I'm pretty sure any ICM you buy today will require only 4 pins. Early on the electronics wouldn't run on 12 volts so 1 part of a dual ballast resistor protected the electronics via that 5th pin. Modern electronics changed things. Some aftermarket modules did show the 5th pin ( prevented end user confusion ) even though that pin wasn't connected to anything inside.
Repeated melting ICM gel coat, overheating resistors, I suspect the coil.
 
Have you checked the system charging/ running voltage? Maybe it's over voltage

^^ As Redfish said, so far as I know, ANY modern replacement ECU is "4 pin" whether it physically has 5 or not. In other words you should only need the single resistor

Also, if you are running a "hot" coil......high output.......it may very well and probably WILL run hotter. If you are, look up the specs and see if it requires a different resistor. Some of them require TWO.....in series, the one for the aftermarket coil, in series with the "stocker."
 
Thanks for the info on the ECU pins. I will use the Duralast ECU for troubleshooting and as a backup.
I replaced the original coil with a stock replacement. No change in voltage and resistance, but it's good to have an extra on hand.
The ballast is a dual resistor in this car.
The negative battery cable has always been in poor shape, so that'll be cheap to replace tonight. I will clean all grounds tonight and let it run for a bit to see if the ECU still heats up too much.
For the short drive around the neighborhood the ammeter showed that it was charging, but not very far from center. I drained the battery quite a bit from all the testing and cranking, so I will see if the charging condition levels out.
 
Sorry to get back so late on this issue. Here is a pic of a ballast resistor with NO ceramic/epoxy fill around the element.

IMG_2840 4.jpg
 
Thanks, mine is a dual resistor and one side blew out. I replaced it, improved all grounds, replaced the negative battery cable, and it runs great now.
FYI, the ballast resistor runs 310 degrees under normal operating conditions, measured with an IR thermometer.
 
On the subject of ballast resister mounting..... When I install a BR I put a 1 inch piece of tubing in back of the BR. This gives a gap for air to flow around the BR. Just get a longer mounting bolt, and put the tubing over the back of the bolt and tighten. this will help keep the BR cooler.

barracudadave67
 
Be sure to check the Ohm's of the resistor your using. If the incorrect Ohm resistor is used an excessive amount of heat will be noticed on the coil and ECU. I cant recall the Ohms that are appropriate for points or Electronic so GOOGLE it but it does matter. This will also affect the way the engine runs, it will run...but not to optimum
This is why a Ballast is supplied in the Electronic conversion kits..it is a total package. Worth investigating. Ballast do run hot...that is a given, how it effects the other components is the issue.
 
Here are what I consider the "big list" of possibilities in no particular order:

1.....Wrong coil/ resistor combination, or a partially shorted coil, or as mentioned, wrong resistor value.

2......so far as hot / melting ECU, Chineseoationized, or other causes listed here

3.......High battery charging voltage. If the running battery voltage is much above 15 (should be 13.8--14.2 with battery/ engine / VR warmed up and "normalized"

4......Something mis-wired causing load on coil+ that should not be there

5.....Do not leave key in "run" with engine stopped. The Mopar ignition is one system that causes coil current to flow with engine stopped.
 
Thanks 67Dart273,
I believe my BR blew because I accidently left the key in the on position a couple times while diagnosing a problem.
Replacing the battery fixed the overcharging issue. It was drawing too much from the system even after I drove it a couple miles to let it normalize.
Thanks for your help.
 
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