I have a 56 f100 with a 302. The previous owner installed a Petronix in the distributor with an unidentified coil. I picked up a Petronix coil but the instruction say you need 12 V at the coil. I checked the existing setup and I have 9.8 V at the coil. I assume this is caused by the ballast resistor on the firewall. Can I simply bypass the ballast resistor and get 12 V? Should I put an inline fuse in the jumper that make up to bypass the resistor? What gauge wire should I use? As you can tell electrical circuits is not my forte.

 

Just bypass the resistor on the firewall.

 

Curiosity is killing me...If you are going to bypass the resistor, what is it's purpose in the first place?

 

The ballast resister is there to cut the voltage down to 6 volts for the coil. Why, I'm not sure. But there was a post about a month ago on this subject and the guys said that they were reutinely bypassing the ballast resister. Now for the confusing part. I installed the pertronix on my 289 with a mallory dist. My installation instructions said nothing about the ballast resister, so I left it in. It works great. Starts easy and runs smooth. 17 mpg for a 54 is pretty good. Is your pertronix not working correctly? Is that why you want to get the full 12 volts to the coil? Just curious. John

 

Here's the simple version - not necessarily correct in all technical points.

There are two types of coils (at least) Some have internal resistors in the case. Others don't. The early ones that we usually run on our trucks need the inline resistor. If you use an external resistor with an internally resisted coil you're sending even less juice to the points.

By the way, in the stock 6V setup the actual voltage at the points is only about 4.2 or less. That's what they were designed for - more than that will burn the points quicker.

 

I am using the standard distributor with the Pertronix electronic conversion, and an Accel coil. Should I not be using the extrenal resistor?

 

The reason why I am changing out the coil is that after talking with petronix they say the system works better with a full 12 V at the coil. I am pulling 9.6 V when I tested it yesterday. There are no markings on the existing coil so I have no idea of the specs. The previous owner told me he intended to change it out for a petronix coil so I took his advice and picked one up. To your point John the truck starts and runs ok but the idle is rough. I am starting to go thru the whole system and figured I'd start with the electrical side first then move on to fuel.

Learning as I go...

 

I called pertronix and they said you can leave the ballest inline but better to give it full 12 volt. I have herd stories of people leaving them in and when they use the light or signals and there is a voltage drop the engine will loose power and the engine, the higher the voltage the better Eed ke6bnl just ast easy to grap a solid 12 volts to run it on. Ed

 

When I installed Pertronix ignition in my 64 F100 I installed Pertronix too. The instructions said to eleminate the resistor. Didn't yours? When I installed Pertronix ignition in my 55 Customline (6V), Pertronix advised me that I didn't need their coil - mine, which has no resistor, would be ok. Both run fine! Install yours per the instructions included, and enjoy.

Norwood Shelton
Retired Control Systems Engineer
Monroe, LA
1964 F100 my dad's, restored
1955 Customline like I had in the 50s

 

MYDad,

The instructions do say that 12V is recommended. My original questions because I am such a novice were: Can I simply bypass the ballast resistor and get 12 V? Should I put an inline fuse in the jumper that make up to bypass the resistor? What gauge wire should I use?

I take from the answers that I should bypass the ballast resistor. But should I fuse the bypass? What gauge wire should I use?

Any additional info would be appreciated.

Thanks to all. I am here to learn and contribute as best I can.

 

I would use number 10 wire to be safe and It should be fused before it gets to the ballast you can just take it out of loop all together for now. But best to have all available and on hand for any failure and need to quickly go back to points. Ed ke6bnl

 

On the back side of the instruction sheet that came with my Petronix Flamethrower coil is a chart that tells you to remove resistor for all 8 cyl applications. I removed the resistor and the coil and pertronix iginition works fine.

 

What size fuse do you suggest?

 

When I installed my Pertronix coil, I installed the same line to it that went to the old coil - I just removed the resistor from the circuit. The existing fusing is still there. Why add another fuse in series with the exisiting one?

 

Thanks for all the advice. If you see a puff of smoke coming from Chicago then you know I messed something up.