so im running a 1972 302 with points ignition, with the car running at idle, im getting around 6 to 7 volts on the distributor side of the coil, and around 11 to 12 volts on the other side of the coil, does that sound right?
should be using a resistor in the coil feed wire. 12 volts will burn the points in short order. I think the resistor drops it to around 5 or 6 volts.I just go to a parts store and ask for an ignition resistor for a 1957 Ford. works for me.
Yep, need a resistor if you want the points to last. But using a resistor will require a bit of wiring; you want the full 12 volts when starting, then drop it to 6 when running. You'll need a Ford starter solenoid with the 'S' (start) and 'I' (ignition) terminals on it, install the resistor in line with the existing coil feed, then run a wire from the 'I' terminal to the coil. Or you could just drop a Pertronics module in eliminating the points and be done...
so it should be reading 6 to 7 volts on both of the ignition coil terminals while the car is running?
It sounds like you are running a coil with a built in resister. If you drop voltage to the + side or your coil it will also drop the voltage at the - side (distributer side). Your points will survive fine @ 9 volts so if you are getting 6 or 7 volts to them you should be OK.
Nope, you'll see a lower voltage on the distributor side due to voltage drop across the coil. Lower voltage into the coil will reduce current (amps) and it's the current that burns the points. You want the resistor for point life...
I need to expand on my above answer a bit... The voltage you're seeing on the distributor side of the coil when it's running is actually an 'average' (or as close as a common hand-held meter can read) voltage. To read the actual voltage, you need to check this with the motor stopped and the points open. This will give actual voltage through the coil, which should be less than the input voltage because of voltage drop across the coil; but if you read anything over about 8 volts it will seriously shorten point life. When the points are closed, you'll read zero volts. Because the points are opening/closing rapidly while the motor is running, the meter is unable to show either actual or zero volts as it can't react that fast. You should also find that voltage as read will go up with RPM. Now there's several other factors that will affect the voltage seen at that terminal when the motor is running, but those require electrical theory knowledge to explain and would require an oscilloscope to show... Bottom line, you need a resistor....
how can I tell if my coil has a built in resistor? so say if i did have a internal resistor coil the voltage i posted should be fine? the reason im asking is because around 2000rpm it starts to run rough, at idle its nice and smooth and also smooth once i stomp on it, so i was poking around in the engine while it was running and when i touched the coil it was really hot, and the engine is in a 53 ford customline, the car has been rewired, i see no ballast resistor, and im not sure if it has a resistor wire.
i went out right now and started the car and the readings were this with a multimeter, while the car is idling, negative bat to positive coil 13.5v, positive bat to negative coil around 7 to 8v, positive coil to negative coil 7.5v
So the car has been converted to 12 volt and if you're still using a stock or stock-type coil, then you definitely need a ballast resistor. I doubt very much that you have a coil with a 'built-in resistor' as Ford never used one (do they even make such a thing?). Note that the '53 didn't have a ballast resistor (because it was already 6V), so if a stock-type harness was installed you won't have the right wiring. And coils will get very warm in normal operation, but if it's too hot to do more than just touch, it's overheating from overvoltage. Whether or not it's the coil causing the rough running is hard to say; I suspect it may be the carb. But the 'voltage' you're reading between the distributor post and ground with the motor running really doesn't tell you anything other than that the points are working. To get an accurate voltage check, you need to check with the motor stopped and the points open.
alright i see, so what is consider normal voltage on the positive side of a coil with a resistor while the car is running?
The factories wanted to see no more than about 8 volts running voltage; more than this, and point life suffered, so this is a good number. One thing they found after going to 12 volt systems was that the car would start faster/easier if the full voltage was fed to the coil while starting the car, but burned points resulted if they tried to run the car like that. So a ballast resistor was fitted into the ignition power circuit to drop the voltage when running, with a 'bypass' circuit that only had power when the starter was 'on' for starting.
If you are interested you could go with a GM HEI distributer made for the 302 Ford engine for around $70 and you will not ned a coil or resister. It is made to run on straight 12 volts. That is what i run on mine and i just love it. Check ebay.
Voltage on the point side is kind of useless because you are going from 0 volts points closed ( a dead short ) to 12 volts points open even with a resister.
so, if running a Pertronix electronic points conversion and coil what results to look for? still need resistor? - '67 Ford 390
You really need to check with the manufacturer of the aftermarket ignition to see what they recommend. Basically it's a question of load; how much load the electronic 'switch' (the 'points') can operate without damage. This should be given in ohms and is measured across the +/- terminals ('primary') on the coil. The higher the ohms, the lower the load. A good 'rule of thumb' is if you add your resistor and coil ohms together, if the new coil's primary resistance is equal to or greater than that total you won't need the resistor. There are some coils on the market now where this isn't an accurate statement; these are designed for 'dwell controlled' electronic ignitions and will burn up if used on a ignition without this dwell control (has to do with 'on' time). Another thing to think about is most older design OEM-type coils (basically, any coil designed for a points-type ignition and many of the early electronic ignitions) weren't designed to operate at 12 volts continuously and can fail if you run them at 12 volts all the time.
On PerTronix, If it is an Ignitor I, we like to see a full 12 volts to the + side of the coil and a coil with an internal resistance of at least 1.5Ω. If it is an Ignitor II, then again 12v to coil + but an internal resistance of .6Ω With points you want a coil and No Resistor, then you want a coil with at least 1.5 Ω internal resistance as well.
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