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By Melly - 5 Years Ago
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How do you know if you should have a resistor on your y block or not? What does it do ( reduce voltage to points? ) and some have and some don’t. I have 1955 Ford Crown, converted to 12Volts purchased already converted. Do see a resistor, it is running a 57 distributor with points.
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By Florida_Phil - 5 Years Ago
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My 1955 Thunderbird had a 1955 distributor with a resistor and 6 volt coil when I bought it. The car had been converted to 12 volts by a previous owner. I changed to a 1957 distributor soon after I bought it. I now have a Pertronix I unit in this distributor with a 1.5 ohm internal resistor coil and no external resistor. Later Fords did not use the external resistor. They had a coil with the resistor built in. If you have a resistor coil, you do not need the external resistor.
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By 57RancheroJim - 5 Years Ago
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After about 1960 they used a resistor wire between the ign switch and coil rather then an external ballast resistor.
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By Tedster - 5 Years Ago
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Long Answer: An external resistor does drop the voltage through the primary side of the ignition circuit, though the actual reason is to reduce the current flow (amperage) as points will otherwise burn up. A points type ignition should not exceed about 3 amperes through the primary circuit. Ohms Law is your friend here when trying to determine what's going on in your application. There are two separate windings inside an ignition coil, the primary, and secondary (high tension).
Ford typically used an ignition coil in a points style ignition system with about a 1.5 ohm resistance in the primary coil winding, and an external resistor of about 1.4 ohms. The external resistor is temporarily bypassed during START, for a hotter spark at the plugs to aid in easier starts. When the ignition key is released to RUN the resistor wire is switched in series with the primary winding of the coil to reduce current flow.
Keep in mind there are probably a half dozen different primary circuit ignition connections and wiring junctions, the switch, etc. The primary circuit resistance is the sum total of all of these taken together. Old wiring, switches, corroded grounds, poor grounding of the distributor housing itself will increase this beyond spec. Shop manual specs have Point resistance measurements to check for this and take it into account, more is not better. The ignition coil is really nothing more than a step up transformer, so as the input voltage is reduced, so is the coil secondary output, and spark intensity at fhe plugs. This is important to check because Voltage requirements are greatly increased when under load, high speed and high power demands. Engine may idle OK, but choke on the road under acceleration demands.
Short Answer: You're probably fine, lol
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By oldcarmark - 5 Years Ago
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Melly (6/3/2019)
How do you know if you should have a resistor on your y block or not? What does it do ( reduce voltage to points? ) and some have and some don’t. I have 1955 Ford Crown, converted to 12Volts purchased already converted. Do see a resistor, it is running a 57 distributor with points.
If at some Point U convert to Pertronix 11 (2) and ad their Flamethrower 11 Coil You do not need the Resistor.
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By paul2748 - 5 Years Ago
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If you have a coil with an internal resistor, then it should be marked as such.
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By Melly - 5 Years Ago
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Thanks again for all great input. Coil printing is not readable, most rub off .
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By MoonShadow - 5 Years Ago
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I run a MSD box with a Mallory Unilite distributor. Following common advice I did not put a resistor in the circuit. Last week, after I got the car out of storage, It would not start. Kept trying but wouldn't stay running. I finally checked the cap. What I found was a badly burnt cap and the rotor had been hot enough that the pointer moved so ignition timing was way off. After replacing the cap and rotor it was not firing at all. Turned out the distributor sensor was also burned out. I don't know what caused this but when I replaced everything I also install a resistor! I also noticed that Mallory sells a fancy resistor box to go with the Unilite!
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