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Ford 9N, 2N & 8N Discussion Forum
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Won't start after 12v conversion

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glennbrown

06-12-2007 18:31:07




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Just did 12 volt conversion to 1950 8n, front mount distributor. New update 12v coil, new alternator, new wiring. Now a negative ground system. Cranks great ! Used to start on a prayer instead of rpm. Now won"t hit a lick. Seems to be little spark at the plug wire, don"t know if enough...anyone ever had problem with new coil ?
Stupid question, starter isn"t turning the engine the wrong direction now ?

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Danny in CO

06-13-2007 12:28:25




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 18:31:07  
I'll try to clarify what the others are saying. If you have a 12 volt front mount coil, you still need some sort of resistor. The original ballast resistor will work, but no other resistors. If your kit came with a resistor, I would probably use it. In this case DO NOT use the ballast resistor also. A 12 volt coil will eventually fail without some resistor. It cannot handle the 14.7 volts put out by the alternator.

First off, use a volt meter to measure the volts at the top of the coil. You should have battery voltage with the points open and about 8-10 volts with the points closed. If you have much less than 8 volts with the points closed, you have the wrong resistor(s) in line or bad/dirty connections. Make sure your points are set at 15 thousandsth. Get a new set of Autolite 437 plug and put in. Keep one out and check for good blue spark.

Good luck,
Danny

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glennbrown

06-13-2007 13:37:30




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 Re: Won't start after 12v conversion in reply to Danny in CO, 06-13-2007 12:28:25  
Pretty clear info Dan...makes sense, I'll recheck the voltage when I get home this evening.



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Hec-In-Omaha

06-13-2007 07:52:07




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 18:31:07  

You need both the OEM ballast resistor and the ceramic resistor wired in series. I have a 49 8N and that's how mine is wired. No problems with the coil.

Hec



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glennbrown

06-13-2007 05:17:44




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 18:31:07  
I only have the new resistor installed. I do have 12v at the coil terminal. Spark is light , will jump the plug, but not a nice blue spark.



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Phil( NJ,AZ,Sask)

06-13-2007 06:56:08




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-13-2007 05:17:44  
Glennbrown, You need to measure voltage at the top of COIL when the Points are "Closed". The 12V (2.5 ohm) Coil will measure ~8.0 volts if the Circuit Resistance is correct. If it reads much higher or
lower you have a problem.

The use of a "single" ceramic (automotive) Resistor is suspect. The proper current of 3 Amps is obtained using the OEM Ballast + (Plus) a ceramic of ~ 1.0 ohm.

Hope This Helps,

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glennbrown

06-13-2007 07:27:23




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 Re: Won't start after 12v conversion in reply to Phil( NJ,AZ,Sask), 06-13-2007 06:56:08  
Ok, if you've read all the replies, now I'm getting a lot of opinions on this resistor.
One guy says to throw it away, another says I shouldn't have both, another says I should use both. Being an older auto guy my belief is that the resistor is there to save wear and tear on the points. Now I am beginning to wonder weather the extra voltage has just done in the points and condenser. Incidently, only have the new resistor wired at this time.

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Phil (NJ,Az,Sask)

06-13-2007 12:18:44




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-13-2007 07:27:23  
The front Mount is not an Auto Coil (unless we count pre-1939). The Current Max is 3 amps or coil will overheat (its the thermo package).
The Auto (Round side-mount) work on over >4 Amps and points (as you said) are the issue. The 1960's dodge used limiting (run Resistor) to near 2 amps, so ignition resistors are all over the MAP, but >2.0 ohms @3 or 4 amps will be Wattage challenged.

Its your choice how you limit current to 3 amps or run unlimited. The results will be measured in coil TIME to failure.

JMHO,

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davpal

06-13-2007 01:39:13




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 18:31:07  
Take the little ceramic resistor and chuck it in the nearest dumpster and you will be in business. BTDT The coils are made to run on a full 12 volts. Later.



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Jack-Illinois

06-12-2007 19:42:27




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 18:31:07  
Is the spring on the bottom of your new coil bent so it does not make contact to the points?



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Bob

06-12-2007 18:48:00




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 18:31:07  
These starters rotate the same dirrection, with either ground polarity. (Per-mag "field" starters DO reverse with a change in ground polarity, however.)

If the starter DID turn backwards, the engine wouldn't be cranking, 'cause the "starter drive" only works "one way".)

If you have even a "little" spark, the coiled "spring thingy" under the coil MUST be making contact with the special brass screw underneath it, RULING OUT that common problem.

What resistor(s) are you "running" ahead of the "so-called" "12-Volt" coil?

For years, Dell has recommended his "trick" 1/2 Ohm, 20 Watt resistor, and, with the coils now being sold, leaving the OEM dash-mounted ballast resistor formerly used with the 6-Volt system seems to be a viable option.

You don't have a weak ignition switch, or an extra resistor in there somewhere, do you?

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glennbrown

06-12-2007 19:12:43




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 Re: Won't start after 12v conversion in reply to Bob, 06-12-2007 18:48:00  
The kit came with a new resistor, white with two spade type terminals, (looks similar to the one chrysler used for years) Pretty comfortable with wiring, and volt meter shows 12v at the coil. I guess it is possible I have flooded it, like I said, I"ve never ever seen it crank this fast before...haven"t pulled a plug. Thanks for your reply. I was grasping at straws with the starter question.



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don b

06-13-2007 11:25:18




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 19:12:43  
Glenn....sounds like your kit had the 12 to 6 volt dropping resistor in it.That resistor is to be used only if you retain your 6v coil.If you have a newer version of the 12v coil[2.5 ohm],I think your original ballast resistor would be all you need.Coil voltage with the 2.5 ohm 12v coil,should be about 10-11 volts with the points closed. don b



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Phil (NJ,Az,Sask)

06-13-2007 12:48:06




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 Re: Won't start after 12v conversion in reply to don b, 06-13-2007 11:25:18  
[quote]I think your original ballast resistor would be all you need.Coil voltage with the 2.5 ohm 12v coil,should be about 10-11 volts with the points closed.[/quote]

Don b, The OEM ballast will not work alone. The (its)resistance @ 3 amps is 1.5 ohms. If we do the simple math 2.5 + 1.5 = 4 Ohms. Then divide the max voltage 14.5V by 4 ohms = 3.6 amps

The OEM ballast will be in/near thermo overload with @ 3.6 amps! It will protect the coil but burn itself out. It needs .83 Ohms of extra help. ~(Near)1.0 ohm Ignition Resistors will work, or even Dell's .5 Ohm resistor.


Since we know the Resistance of the Coil (2.5) its simple to calculate the correct Voltage Drop Your 11 volts = 11/2.5 = 4.4 amps and is Wrong!
Now if the coil is ~ (near)4.0 ohms you would be right

JMHO

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Ramrod

06-14-2007 08:25:40




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 Re: Won't start after 12v conversion in reply to Phil (NJ,Az,Sask), 06-13-2007 12:48:06  
Hey Phil, do you know the wattage rating for the OEM ballast resistor (18-12250) or today's replacement?



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soundguy

06-12-2007 21:14:48




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 19:12:43  
You don't have the oem AND the new resistor installe ddo you? that could be the problem.. that or your points aren't closing / are dirty / coroded.. etc..

Soundguy



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Bob

06-12-2007 19:28:31




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 Re: Won't start after 12v conversion in reply to glennbrown, 06-12-2007 19:12:43  
Is the coil labeled "12-Volts"?

Is the OEM ballast resistor still in the circuit?

The voltage at the top terminal on the coil should = battery voltage, with the engine stopped with the points "open", or somewhat less if the points are closed.

HOW MUCH less will depend upon what coil you have, and what resistor(s) are ahead of it.

If you DON'T see the voltage at the coil's top terminal drop when the breaker points are closed, you have an "open" between the coil and the breaker points, or the points are mis-set or dirty. (REMEMBER... you have resistor(s) ahead of the coil... the voltage is dropped across the resistance.

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DEERHUNTER1

06-13-2007 06:39:34




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 Re: Won't start after 12v conversion in reply to Bob, 06-12-2007 19:28:31  
i just did a 12volt conversion on my 8n,it wouldn't start at first.i switched the key switch wires around and it fired right up.of course i'm far from an expert and now i'm stuck in 2 gears so take it for what it is.



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