Having a heck of a time locating a 12V source that got when the key is on and cranking position. All the sources in the fuse box are off during cranking which will not serve the Pertronix during startup. Thought about running a line from the I terminal of solenoid but it continues to feed 7V in run. Truck runs excellent with 12V to the Pertronix and less so with 7V source.

any fellers or felletes know a wire I can snag for a 12V hot/crank source?

1970 F250 manual

thanks in advance !

 

take the resistor out of the 7v wire and you're good to go. Or if you want to leave it there splice in before the resistance wire and feed the pertronics.

 

I thought about adding a wire to that resistor circuit but I was concerned about overloading the switch itself. I’ve had a couple of these switches short, one due to the wrong coil being installed and it overloaded the pink resistor wire. If the switch contacts and power source can handle an added 12V feed being added to that pin with the pink wire, I’m all about it.

I’m currently using the pink wire to power the new coil, and it’s fine by itself. Just hung up, gun shy of running more power through the switch. But maybe my concerns are unnecessary and it will handle it fine.

 

Are you not using the original coil wire? You wouldn't be adding anything to it.

 

I agree with @tcanthonyii . You can just splice into the stock ignition wire before the resistance section. I'm not sure on these trucks, but on the early mustangs the ignition wire is red/green and the resistance section is pink... I would expect it might be so on these as well. You're not really adding extra load. You're actually removing some since you're bypassing the resistance section.

If you're not comfortable with that you could use the stock ignition wire to trigger a relay to feed 12v straight from the battery.

For what it's worth, I have been running my Pertronix 2 and Flamethrower 2 coil on the stock wire with the resistance wire still in place for nearly 20 years with no issues, on my '67 Mustang... your mileage may vary... I know some have reported issues doing it this way.

 

I am using the original resistance wire to power the coil, like stock.

 

Unfortunately when I ran the coil and Pertronix from the pink wire and it resulted in the wire getting really hot. The pink wire supplies around 7V to the coil and I can see a big dip in idle quality over running 12V to the Pertronix.

 

unfortuantely the ignition wire off the Solenoid only provides 7V so I’m concerned about it keeping the relay triggered. The 12V bump while cranking would definitely activate the relay, I’m just assuming when it dips to 7V in the run position it will open the relay and kill power to the Pertronix.

leaning toward trying to splice power into the switch.. still a bit nervous about overloading it. Seems Pertronix doesn’t know what the amperage draw is on the 1281 unit

 

I think that's your best option. I always intended to go back and do that on my mustang, but it runs great as it is (with the resistor wire still in place) so other things seem to always take priority.

I don't know the amperage draw of the pertronix unit, but I know you'll be decreasing the load by removing the resistance wire, then just adding a small amount back with the pertronix. It'll certainly be less than mine which is pulling the same load through the resistance wire. You'll be fine.

 

The brown “I“ wire from the starter relay/solenoid is only 7 V because it is actually being fed from the resistor wire when the key is in the on position.
It only gets 12 V in START from the battery, to feed the ignition system beyond the resistor wire.
Once you turn it back to run/on, all the power is coming from the ignition switch via the resistor wire.
Not actually coming from the I terminal.

The other source for 12 V in start and run, but not in ACC, is the green with red stripe wire from the voltage regulator.
You could tap into that for the distributor section and keep the resistor wire powering the coil. That should run well. in theory…🙄

The relay idea works very well.
You can usually only feed both the coil and distributor from the same wire when it got full voltage.
Using the resistor wire for both “usually” gives you a poor running engine.
I said usually because obviously right here it was mentioned that theirs has run fine for 20 years.
That’s what we found in the Broncos as well. About half of them ran great, and half of them ran like crap.
Since resistor wires do vary slightly, with some giving out less voltage than others, perhaps that’s the difference?

Anyway, try a relay, or try the green with red voltage regulator wire.
If you’re not sure how relays work (basically just a remote switch), let us know when we can run it down for your here.

 

thanks for the info, I like to idea of pulling off the regulator better than from in the cab. I’m pretty well versed in relays, just had a heck of a time finding a reliable keyed 12v trigger. I’ll be working on it today, I’m going to see if I can locate and test the aforementioned green/red wire.

 

https://www.fordification.com/tech/w...-70_master.jpg. The "I" terminal on the starter solenoid should always be 12V. The "S" terminal with the brown wire should always be 12V. At the coil in Start should be 12V and in Run should have reduced voltage. On my 70 f250, I bypassed the resistor wire with a new wire to supply 12V to and HEI distributor. Since then I have gone back to the original distributor with Petronix in it with the 12V supplied in Run as well. If I had to do it again in this truck, I would have just ran the resistor wire through a relay and brought 12V from the battery.

 

Just a couple of added details (and a correction) to browski's information:

The "I" terminal has 12v when the relay/solenoid is energized when the key is in the START position. Which is probably what was meant by "always" in this case?
But otherwise, any power seen at this terminal is coming from the Brown wire attached to the resistor wire. So you will see reduced voltage on this terminal in the normal course of running.
If the Brown wire is disconnected, the "I" terminal has no power except in START. If it does, then the relay is defective/busted.

This terminal actually has the Red w/blue wire. Not the Brown wire.
The Brown wire is on the "I" terminal.
This terminal has 12v, but again, ONLY when the key is in the START position.
Which is again, probably what 1browskit meant, but I wanted to clarify. So "always" is only when the key is turned to START.

In theory...

Paul

 

The "S" terminal is the ignition source and is always 12V coming from the ignition switch. https://www.fordification.com/tech/w...m-72_quick.jpg. The brown wire is off the "I" terminal and goes to the coil but the wire changes color where it and the resistor wire meet before continuing to the coil. So, while in start, 12V power comes from the battery to the coil. While in run, 12V power comes from the ignition switch, then through the resistor wire to the coil. Yes, when I mentioned the "S" terminal was always 12V, I meant as in there is no reduced voltage at the "S" terminal.

I had to edit this. I totally had the I and S switched around. I took a picture of my 72 f250 wiring but didnt look at it. Then I was just looking at my 70 f250 and realized I was switched around on the starter solenoid. Sorry for the confusion