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EFV-8 Club Forum / General Ford Discussion / Ignition Primary Voltage

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Posted By Discussion Topic: Ignition Primary Voltage     billcarry 04-25-2017 @ 2:49 PM reply profile send p.m. Member Posts: 55 Joined: Jan 2016 On my 48, the primary resistor is mounted on the coil which I think is correct. The primary voltage is about 5.8 volts. This seems low. the battery is 6.3v. I think the person who restored the car a number of years ago replaced most of the wiring harnesses. Couple of questions: Did all the 48s use the coil mounted resistor? Any chance there is the underdash resistor in the present wiring and if so where was it located? Can I run full battery voltage from the starter solenoid to the coil primary just when cranking? I have random hard staring. cliftford 04-25-2017 @ 3:38 PM reply profile send p.m. Senior Posts: 845 Joined: Jan 2014 Yes you can do this by running a circuit from the starter side of the solenoid, through a diode and then to the battery side of the coil. This message was edited by cliftford on 4-26-17 @ 6:10 AM 40 Coupe 04-26-2017 @ 4:59 AM reply profile send p.m. Senior Posts: 1678 Joined: Oct 2009 No resistor under the dash. With the distributor points open you should read near battery voltage on both sides of the resistor. With the points closed battery volts on one side and ABOUT 3.5 to 4. volts on the other. You may want to clean the brass terminals of the ignition switch and the coil and it's resistor. None of these will make your car starter motor turn over faster! Cleaning battery terminals and engine ground connections for faster starter motor operation and check the starter solenoid to make sure battery voltage is not being lost internally through it's contacts. juergen 04-26-2017 @ 6:12 AM reply profile send p.m. Member Posts: 258 Joined: Jan 2010 I think you have a typo. Running the wire to the battery side of the solenoid will place battery voltage to the coil all the time. I think you meant to the starter side of the solenoid. cliftford 04-26-2017 @ 7:09 AM reply profile send p.m. Senior Posts: 845 Joined: Jan 2014 Yes, that's what I meant to say. I did edit the original post. Thank you for pointing this out. TomO 04-26-2017 @ 7:10 AM reply profile send p.m. Senior Posts: 7256 Joined: Oct 2009 All 1948 cars had the ignition resister on the coil. This was incorporated in 1947 when the sea sh*ll horns were introduced. If you have an aftermarket round coil, most of them have an internal resister and the external resister is not needed. To determine if you have excessive resistance in the primary circuit, connect the COM lead of the voltmeter to the NEG battery post and the +or red lead to the ignition switch side of the ignition switch. Turn on the ignition switch, and tap the starter to close the points, the meter reading will increase when the points close. The meter reading should not be above 0.2V. If it is above 0.2V, move the red lead to the ignition switch input (y-b wire) and recheck. The new reading should not be above 0.15V. If this reading is OK the switch is dirty or corroded. I don't remember if the 48 key ignition switch can be disassembled for cleaning, the toggle switch on the column can be cleaned. If the reading is OK, turn the ignition switch on and off several times to see if the reading changes. If it does change, the switch is corroded. To provide full battery voltage to the primary side of the coil during starting, run a wire from the starter side of the solenoid to a diode and then to the primary terminal on the coil, leave the ignition resistor in the circuit just as it is, or you will damage the coil and burn the points. This circuit is not necessary if the primary resistance is within specifications and the coil is good. It will not provide battery voltage during starting if your coil has an internal resister. Tom This message was edited by TomO on 4-26-17 @ 7:27 AM MGG 04-26-2017 @ 2:48 PM reply profile send p.m. Member Posts: 85 Joined: Jul 2014 Is there any particular type/brand/or model of diode recommended? cliftford 04-26-2017 @ 8:44 PM reply profile send p.m. Senior Posts: 845 Joined: Jan 2014 I used one that was intended for replacing the generator cut out on a model A. Most ford parts houses should have them for around $4. Or check with a electronics store and tell them what you are using it for. supereal 04-27-2017 @ 11:53 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 I have used the diode quick start circuit for years. We use the "top hat" style diode. As it is a bypass, it doesn't carry much current. One important factor: be sure the diode is "facing" the right direction. To check it, remove the bypass wire from the coil input and place a voltmeter between that wire and ground. When you run the starter, you should see battery voltage. If not, turn the diode around and try again. For safety sake, be sure the car is out of gear and the ignition switch is off when testing. Also, be aware that the bypass will allow the engine to run as long as the starter button is pushed. If you need to "bump" the starter when working on the engine, disconnect the bypass to prevent the engine from starting while you are under the hood. Drbrown 04-27-2017 @ 8:55 PM reply profile send p.m. Senior Posts: 570 Joined: Nov 2013 For what its worth .... I recommend checking under your dash board for an ignition resistor mounted on the circuit breaker board. Even if there, it may have been abandoned at one time. I say this because my '47 has its ignition resistor mounted under the dash on the same small panel board as the double circuit breakers. As often noted, '47 was a year of many changes (mostly body parts I thought) but maybe the location of the ignition resistor was one of those variables along the assembly line. This message was edited by Drbrown on 4-27-17 @ 9:02 PM

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