Ballast resistor

O

Ovenbird

RAL
I installed a Bosch electronic ignition (square sliver box) from Matt at Midwest when I restored the car 12-years ago. The Bosch kit included a ballast resistor, which I also installed. I understand the resistor is typically associated with points to reduce current flow and voltage to the points. I measured a voltage drop from 12 to 8 v across the resistor.

Is the ballast resistor needed with the Bosch ignition?
 
As you know the electronic ignition system does not have points. So the ballast resistor is not for that purpose here, but it is still a part of the electronic ignition system for other reasons. It will also depend on what coil you are running with the Bosch control module (box); some coils have a built in resistor.

You might also want to look into the ignition module upgrade using a GM module in place of the Bosch box. There are good threads discussing it. I believe they are tagged in the "best of" portion of the workshop forums.
 
Thanks for the info. I was just curious about the function of the ballast resistor, and you guys have answered that for me. I will continue to run with the Bosch electronics. If I upgrade, I have several points type distributers and can install a Pertronics unit.

Thanks again for the help.
 
Ovenbird said:
Thanks for the info. I was just curious about the function of the ballast resistor, and you guys have answered that for me. I will continue to run with the Bosch electronics. If I upgrade, I have several points type distributers and can install a Pertronics unit.

Thanks again for the help.
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The nice thing about the GM ignition module upgrade is it only replaces the Bosch "box". The rest of the Bosch electronic system (distributor, harnesses, etc) are still retained to use with it. That gives the same benefits of the whole Bosch electronic ignition but with a little better "guts" for the brains of it (the actual control module part). You can even install the GM module inside the Bosch box if you want to keep it looking original. That is also described in those prior threads I referenced.
 
The ballast resister is for the coil not the Bosch box

A coil which doesn’t need the resister could be used instead. The GM chip is a superior solution from a power consumption perspective and presumably performance.

Edited. Based on the further conversation below I believe the lined out section of this statement to be erroneous.
 
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dllubin said:
With no resistor, the coil current could more than double and that could fry the box.
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The coil is on the other side of the box electronically. The box is seeing the full 12v, the coil is what has to run at 8/9volts and will overheat the coil if run at 12v and thus requires the ballast resister.

Edited: See above
 
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kmead said:
The coil is on the other side of the box electronically. The box is seeing the full 12v, the coil is what has to run at 8/9volts and will overheat the coil if run at 12v and thus requires the ballast resister.
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The box is what switches the coil current. That is where most of the power dissipation is.
 
I accede to your degree and work experience… Thank you.
dllubin said:
The box is what switches the coil current. That is where most of the power dissipation is.
Click to expand...

I am a fan of the GM chip and being able to use a hotter coil without the ballast resister which it enables. Using the 124 Spider coil and heat sink is a nice “Fiat” solution which requires minimal rewiring even if it doesn’t look X original.
 
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