Ive got a 40 Ford 60HP V-8 in my 31 pickup. Yesterday it died on the street. With a test light I traced it to a bad resistor before the coil. I replaced it with a spare under the seat and made it a few blocks. Then that one failed too!! Both were non ceramic style. I wired + wire direct to the coil just to make it home, and it runs great. Is there any NAPA or other local part that would work? Im worried Ill cook the points if I run it without. Thanks
Is the coil stock Ford '37 type or something else?? NAPA Echlin replacement is ICR 40, listed as .35 ohm resistance. Standard # is FD-220 Worry about coil, wiring, points here...normal resistor life expectancy is probably longer than ours.
OK, what is source and number of coil?? Resistor needed depends on coil...best to attach things to an OEM application or a specific catalog so resistor need can be found. Many 6V coils like A-B, '49 Ford run on straight 6V.
It's a flatheadv8 Ron. I know you know your electrical systems as you have taught me a few things. Assuming your using a 6 volt system right? Some new coils are made for electric ignitions. Low resistance 0.6 ohm coils. So as Bruce said find out what you have.
I realize it was a V8 but I was just showing the 6 volt system. We have used as low as .6 ohm coils with points on a 6 volt system with no problems. Remember when you use a resistor in a 12v system you are trying to get down to 6-8 volts, you're already there with a 6 volt car.
I didn't see that he posted that is was a 6-volt car anywhere. 6-volt coil yes. No offense suggested Ron. Maybe he has a 12v car with a resister for the 6v coil that is burning out?
Title..."6V Flathead ballast resistor failure " Is flathead distributor but not coil...so quite possible resistor is wrong or unnecessary
Its an older coil and has no markings on it. Im just gonna run it with 6 volts going to it and see what happens. Thanks for the help Rob
GMC Bubba's coil test. Doesn't test if the coil is good when its hot but a great way to see what the coil is. http://www.jalopyjournal.com/forum/showthread.php?t=457307 You should have a resistor right? Model A coils don't need them but newer ones (to my understanding) do? Correct? 1940 passenger car.
That coil doen,t need a resister,with a 1.5 omn in line draws 3 amps x 1.5 and drops 4.5 volts cross it and burns 12 volt draw less amps.I think Ford is the only one that uses a resister with 6 volt system up to 48 then 49 no resister.
Ha ha sorry Don, some how I hybrid'ed rod/don. I'm working and in between computer renders I'm hamb'in. I guess I need to leave my multitasking to 3 things at one time.
I had to do a little hunting http://www.jalopyjournal.com/forum/showthread.php?t=454923 Scroll down the photos. The truck has an 8 volt battery in it and that is probably the reason for the resistor. Sweet little truck all around with an interesting history.
Aha! A revelation! 8V battery equals lots of electrical replacements. Voltage regulator has to be teased to run one of those, so working voltage is higher than 8...
Good one. So the best/easiest fix would be a 6 volt battery instead of the 8v right. I'm still not clear on the ballast resistors though. Most posted here have said you don't need a resistor/ballast for 6 volt coils. So why are there factory underdash ballest from ford in the 30's? Does the ballast act like a voltage conditioner? Does it reduce voltage/ohms? Please humor me, I would like to learn.
I got rid of the 8 volt battery when I got the truck. It was shot from sitting for 7 years. It has a 6 volt battery. Rob
On a 12 volt system... The resistor is there to drop the 12 volts (actually more like 13.8 volts) from the cars electical system down to 6-ish volts for the coil. Don't panic, almost all cars are set up this way. Here's why: (Very generalized discription follows. Your mileage may vary!) When you try to start the car, and while the starter motor is cranking the engine, the current drain on the battery is so high that the electrical system voltage drops (Every noticed how the lights sometimes flicker if you try to start the car at night with the lights on?) by as much as half. So we install a 6 volt coil in the hope that it will be able to produce enough of a spark to start the engine while it's beeing cranked. But, after the engine starts and the alternator goes to work recharging the battery, the system voltage comes back up to 13.8 volts. So, as soon as you release the key switch from the start position, that resistor is switched into the coil primary circuit to reduce the voltage to 6 volts, and the coil is happy
Better help me out here , my math just went tilt ! A .06 resistor would have the potential ( using ohms law) to draw 100 amps !!! A .60 ( little larger than 1/2 ohm) would draw 10 amps. The Model A contacts wouldnt handle either for long. Did you actually mean to say .06 ????
If you connect it direct to the coil you run the risk of burning your points out depending on the coil. Being that the previous owner had a 8v battery in it, he may also have had the knowledge to have upped the generator output level to charge it. You might be charging at 8-9 volts. I'd say he had it there for a reason. http://fordbarn.com/forum/showthread.php?t=15305&highlight=ballast
I don,t think it was a Ford resister 6 or 8 volts wouldn,t burn it out. The .5 ohms can easyly handle 3 amps.If some used a resister with a lower power WATT rating it would burn out. The Ford resister my guees would be a rating of 5 watts. Any way no resister is needed on 6 volt coil other then Fords before 1949.
Sorry Jim, Total Brain Fart - Yes .6 OHM coil, not .06. That'll teach me to answer stuff on here in the middle of writing an exhaust technical article for a new book.
WOW ! THIS HAS BECOME THE GOOD , THE BAD AND THE UGLY OF ALL IGNITION THREADS !!!!.. Let address the orginal problem , i think thats what the poster wanted .... Heres what we know . its a flathead using the old style distributor with remote coil and a six volt battery. Heres what the factory bullitens say from April 1938: The normal resistance of the ford V8 primary circuit is 1.00 to 1.35 ohms. If the resistance of the primary is less than normal , then more current will pass thru the primary and shorten the life of the breaker points. So if we know what the resistance spec is actually then we can calculate the actual amps needed for proper spark. 1.35 ohms divided into 6 volts = 4.4 amps or the spec current for this system. This 1.35 could be a .35 resistor and a 1.0 ohm coil or any combo of the two. IE= No resistor would just need a coil of 1.35 ( i would suggest a 1.5 to lower contact current) If a resistor is used it would need to be watts=volts x amps so 6 volts x 5 amps would = 30 watts..... Ok now that we have the numbers correct ( whew that took a few of us) Lets fix this car......... Get a oil filled coil of 1.5 ohms etc hook it up direct and start the engine and drive it !!!!!! No resistor needed !!!!!!!!!
"Get a oil filled coil of 1.5 ohms etc hook it up direct and start the engine and drive it !!!!!!" "Oil-filled?" Bubba slipped a little wisdom in there. Some of the special rebuilt coils are not oil-filled and may not take the heat and abuse of the originals. Doing the math wrong can be expensive ... er, explosive. He also did not tell you another one of his secrets ...
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