What's the voltage at the coil + terminal?

When out to the 51 and took some measurements.

It's a 51 Plymouth Cambridge I converted to 12v negative ground using a Mopar alternator and voltage regulator. Stock points ignition with Mopar ballast and 12v coil.

engine off, key in run I see 12.2V at the battery (low, should be 12.8v ish) and 6.2v at the coil +, all grounds taken at the battery negative terminal.

engine running, 12.8V at the battery (low, should be 13.8v ish, need to up the idle speed) and 8.8v at the coil +, all grounds taken at the battery negative terminal.

Pertronix says 8.0v minimum. You barely have the minimum for a 6v system. You aren't still running the ballast?

A LINK to the Pertronix test pdf.

For some reason your voltage at the coil is way low.

With the key on, engine off what's the voltage on both sides of the ballast?

One side had better be real close to battery voltage. that side comes from the ignition switch.

Pertronix failures are common.

Did you use their coil also?

If so, swap the old one back in & try it.

Only did the conversion with the distributor.

The ballast resistor has two feeds from the ignition switch, one from the run position and one from the start position for feeding the coil + side 12.+ V when the starter is engaged. Once you turn the ignition switch in the run position you should see 12.+ volts on one side of the ballast resistor and around 6.0 to 8.0 volts on the other side going to the + side of the coil.
You should also see 12.+ V on the + side of the coil when you have the ignition switch in the start position also
If you have both of those voltage I would think the Pertronix module is the problem
Do you have a trouble shooting procedure for the Pertronix unit?

Jump 12V to the Pertronix & if no go then its the P conversion in the dist that's at fault

Going to check and see what it is.

What voltage on both sides??

Only getting 5.5 at the positive side of the could in the on position. Is there a way to bypass the ballast resistor temporarily to see if the car starts?
If I dont have 12 volts at the ballast resistor, what is the fix for this?

This is normal, now get someone to hold the ignition switch in the start position after you are ready to read the voltage going to the + side of the coil when the starter is wroking
let us know that voltage
Did you check the voltage on both sides of the ballast resistor with the ignition switch on? If not do that, one side should read around 12.+volts and the other side should read less than 8.0 Volts if you check it before it warms up and creates more resistance which will read less voltage like you have seen.

11.8 is low, really low. What is the voltage at the battery terminals. Should be 12.6 or better.

You could try running a jumper from the batter + to the side of the ballast that reads 11.8 right now and try to start it. If it runs remember that you won't be able to shut it off till you pull the jumper. and it will narrow theisue down to before the ballast.

Curious still 5.5 at the + side of the coil when in the on position. Why would this be? What would the distributor have to do with this?

The ballast resistor is dropping the voltage to the coil like it was designed to do
The Petronix unit may be dropping it more than stock also

Install a used, original 50 year old coil & send the 'new' Petronix one back also while you are at it to save on shipping.

Have 12.0 volts from the blue wire to the positive side of the coil.
Weird but when you hook up the ignitor positive wire to it, it goes to 5.6 volts.

Kinda late to the party... glad you solved your issue though


I read thru the thread, and I'll just mention that I've been using Pertronix conversions on my personal/customers vehicles/equipment/marine applications as well for about 30 years now without a single failure/issue to date....

I've found thru the years that most failures that others experience are from mismatched components, or improper installation, or not knowing some of the peculiarities of the various Pertronix systems...

You should eliminate the ballast resistor (I understand your need for an OEM look) to have a true 12 volts to the HallCell, just gut out the stock ballast resistor, and solder in an insulated piece of copper #10 or #12 wire between the 2 terminals, connect the harness terminals on the resistor as you normally would, the system will run so much better, and you will have eliminated a weak link in the system as well... for no resistor in the system connect the black Pertronix lead to the NEGATIVE terminal on the coil, and the RED Pertronix lead to the POSITIVE terminal on the coil, your BLUE/DARK BLUE ignition lead from the vehicles bulkhead will go on the POSITIVE terminal of the coil

Your running the Pertronix I, it has no internal safeguard to protect the HallCell if the key is left in the "run" position for more than 30 seconds without the engine running, if you must troubleshoot the electrical system in the future with the key in the "run" position for long periods of time, disconnect the RED Pertronix lead from the coil...

I'd recommend using the Pertronix Flame Thrower coil/epoxy filled, but if you insist on the OEM coil, make sure it's rated for 1.5 ohms for the Pertronix I on a V8 application

Run a copper terminal cap, avoid an aluminum terminal cap, no solid core plug wires ...

Just some tips to help you avoid any issues with your new Pertronix install




Mike

That's because without the ignitor hooked up you have an open circuit and you will read battery voltage at the coil +. That's the nature of an open circuit.

You did good troubleshooting it, next time you'll be more confident in you abilities.