Ballast Resistor mounting

Banjer Picker · Apr 7, 2019

Any recomendations on where you guys typically mount this?

Painless install instructions just say firewall. Any recommendations specifically where on the FW that makes a good home for it?

1strodeo · Apr 7, 2019

somewhere where NOTHING will touch it!!! it gets super hot

SHX669 · Apr 7, 2019

I built a small aluminum bracket to get it further out from the firewall .
I installed mine on the same side of the engine bay as the coil - since that's where the wire from the resistor goes to.
You also want to get a spare ballast resistor just in case that one gets too hot and fails.

Banjer Picker · Apr 7, 2019

SHX669 said:
I built a small aluminum bracket to get it further out from the firewall .
I installed mine on the same side of the engine bay as the coil - since that's where the wire from the resistor goes to.
You also want to get a spare ballast resistor just in case that one gets too hot and fails.

Wow. Didn’t know they could possible fail.

DirtDonk · Apr 7, 2019

They don't fail that often, but anything that gets that hot and that is made in China now, is more likely to fail than say, the ones made 40 years ago.

And I don't know how the factories mounted them straight to the body panels, but they must have been made differently, because the ones you typically get from the aftermarket will burn the paint right off of any panel you mount it to.
And no matter what, the first time you fire things up don't panic when you see smoke coming out of it.%)

And if you have new paint, don't mount it to a body panel directly. Do what was said and either use a bracket or make a stand-off of some kind. Most just add washers or a spacer to get an air gap behind it so that it does not melt the paint.

Or better yet, if it's an option for your build, get ignition components that don't need a resistor and just run the straight 12v to the ignition and be done with all that resistor/heat stuff.

Paul

ransil · Apr 8, 2019

I used aluminum heat sinks, my wife was a TV repair person so i had a pile of them.
a piece of aluminium should be good enough to keep it off the paint.
I always mounted them next to the dura spark module.

SHX669 · Apr 8, 2019

Banjer Picker said:
Wow. Didn’t know they could possible fail.

When I was still running the Duraspark II with Painless harness I had one ballast resistor fail .
Back in the mid 1970s some of the Chrysler vehicles had firewall mounted ballast resistors . Most owners I knew learned to keep a spare In the glovebox.

Banjer Picker · Apr 8, 2019

Thanks for the feedback.

What are the symptoms of a failed resistor?

Out of curiosity is there any reason why a company like Painless would use something with a potentially substantial fail rate. Are there no alternatives? My factory harness didn’t have/need one. Why add something like that in?

Would an Oreillys be a good source for a spare.

Thanks again gang

SHX669 · Apr 8, 2019

Not saying the ballast resistor has a substantial fail rate just that it's the weakest part of the system. It's a coil that has electricity going though it { a resistor } and it gets pretty warm . Same as an incandescent light bulb and it's filament.
Your factory Ford wiring had a resistor wire built into the " run " circuit . The painless harness doesn't have a resistor wire so it uses the external ballast resistor.
If the resistor goes bad your motor won't start or run as it supplies power to the coil.
Any auto parts store should have one but you need to get one with the correct amount of resistance.
It's been awhile since I've messed with this stuff and I don't want to give you bad info so hopefully one of the knowledgeable guys will chime in ---but don't run a coil with an internal resistor if you're using the ballast resistor. Also I think the Duraspark system requires the resistor -- I think - LOL . The Painless install manual has some good info about that.

DirtDonk · Apr 8, 2019

With the Dura Spark, only the coil needs the resistor. The modulator/module/spark box/thingy is usually connected to full voltage.
There were a very few (maybe one?) model of Dura Spark module that seemed to have a resistor in the diagrams, but most diagrams show no resistor for the box.
If you're using the most common "blue grommet" module you'll be ok using it only for the coil.

Paul

Banjer Picker · Apr 8, 2019

Mine is a ‘73 so no Duraspark. It just has the regular distributor and I installed a pertronix unit into it.

DirtDonk · Apr 9, 2019

Well I say that's a good thing and have a recommendation then.
Get a coil that's designed with the proper internal resistance and don't use the ballast resistor.

Your Pertronix Ignitor in the distributor wants the full 12v supplied to it, so does not want a resistor.
The coil is the only thing in that case, so if you can avoid the resistor entirely I'd call that a win for both simplicity and reliability. No worries about heat, or one additional component to fail (I agree that they rarely fail even though they can), and no worries about the right resistance, which one to get as a spare, etc.

What coil are you running now? New or original?
If it's an aftermarket coil what is the part number and resistance value. It's usually printed on the outside, or if you have a receipt with part number that would be great.

Paul

eric0o1 · Apr 10, 2019

Banjer Picker said:
Would an Oreillys be a good source for a spare.

yes you can pick them up at most auto parts stores. However, as others have said, if I'm going to the parts store, I'm buying a coil that doesn't require a resistor instead of purchasing another resistor.

If you need a new resistor, RU11, is a good part number most stores should have in their system or be able to cross reference.

Banjer Picker · Apr 19, 2019

DirtDonk said:
Well I say that's a good thing and have a recommendation then.
Get a coil that's designed with the proper internal resistance and don't use the ballast resistor.

Your Pertronix Ignitor in the distributor wants the full 12v supplied to it, so does not want a resistor.
The coil is the only thing in that case, so if you can avoid the resistor entirely I'd call that a win for both simplicity and reliability. No worries about heat, or one additional component to fail (I agree that they rarely fail even though they can), and no worries about the right resistance, which one to get as a spare, etc.

What coil are you running now? New or original?
If it's an aftermarket coil what is the part number and resistance value. It's usually printed on the outside, or if you have a receipt with part number that would be great.

Paul

Howdy Paul, revisiting this as well. Do you know where I would get the proper internally resisted coil so that I could eliminate the ballast resistor?

DirtDonk · Apr 19, 2019

Which Ignitor model do you have? A I, II, or III?

Paul

Banjer Picker · Apr 19, 2019

DirtDonk said:
Which Ignitor model do you have? A I, II, or III?

Paul

Crap, I have no idea. Bought it 7 years ago and don’t even remember there being options. Seems like I just bought the one at the parts store. I didn’t change out my coil or anything.

The number on the black cube inside that the pos and negative wires go to is 47U-V4. I’ll email you a pic.

Sorry, this is outside my wheelhouse man. Trying to learn as I go!

Banjer Picker · Apr 19, 2019

Emailed the pics and a little more info to you Paul.

DirtDonk · Apr 19, 2019

Got 'em, thanks!
It's an Ignitor I model. You can tell because it's got a black body, where the Ignitor II would be red. And the decal on the side would have indicated Ignitor II anyway, as opposed to just saying Ignitor.
So now we know what you have, I'll see what Pertronix coils are recommended and work from there with different brands if that's what you prefer.

Paul

Banjer Picker · Apr 19, 2019

DirtDonk said:
Got 'em, thanks!
It's an Ignitor I model. You can tell because it's got a black body, where the Ignitor II would be red. And the decal on the side would have indicated Ignitor II anyway, as opposed to just saying Ignitor.
So now we know what you have, I'll see what Pertronix coils are recommended and work from there with different brands if that's what you prefer.

Paul

Sounds great! Thank you.

DirtDonk · Apr 19, 2019

According to Pertronix, you can use their 1.5ohm coil with the full 12v (no resistor) if using an Ignitor I on a V8 engine.
If the same setup on a 6-cylinder engine, you'd want to keep the resistor, or go to a 3.0 ohm version

This is the one we sell for that: https://www.wildhorses4x4.com/product/Flame_Thrower_Coil_Black/Bronco_Performance_Ignition

That is their #40011 coil, but they also have an epoxy-filled version #40111 for higher heat and vibration resistance. They recommend those for harsh environments like air-cooled engines or hard running off-road.
It's the one I've used in both the Corvair turbo and Bronco in the past (prior to switching over to computer controlled stuff).

If you prefer to use something from MSD or Mallory or other, you should verify the same characteristics and recommendations for their 1.5 ohm coils. Just to be sure they abide by the same parameters.

Paul

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