What should the voltage be at the coil on 46 6volt positive ground?

[Big_Guys_baby]

Hey Barners! I am in finishing stages of getting my 1946 Ford Business Coupe on the road for real. Still having some intermittent electrical issues and hot starting problems. Distributor was just rebuilt by Bubba's, all the wiring has been replaced. New brushes on generator, lots of grounds throughout system.

The coil has been on the car for a few years and I have no clue where it came from or its specs. I am getting 6.3 volts at the battery, 6.2 volts at the ignition switch, and I am getting 2.9 at the coil. It is running an external resistor under the dash. I haven't done a voltage test at the coil while cranking or tested the resistance at the coil. I picked up an IC-7 coil from napa, thinking about bypassing the external resistor and putting that on to see if I get better starting and running.

Car is still 6 volt positive ground.

Thoughts???

Thanks!

Jeff

[41panelmark]

I had similar issues with mine, I replaced the resister with a new old stock piece as well as cleaned and tightened all of the terminals both ends. So far so good but would like to see what others have to say.

[George/Maine]

You can run that IC7 with NO resister.
Note The wire end look and see if they are held on by coating and few strands.
Good yank may pull the end off.

[Bolts]

You can put the volt meter directly across the resistor terminals with the ign on (with points closed) and see what the voltage drop is on the resistor. Should not be more than about 1 volt or so. If it's higher, bypass the resistor and measure the voltage at the coil + side.
Also, which side of the ign switch are you measuring? If the "ign on" side of the switch is near 6V, you must have a bad connection to the coil. If the "ign on" side voltage of the ign sw is low, you must have a bad contact in the ign switch.
Hope this helps.

[koates]

Hi there, with the distributer timing contacts closed which means the coil is energised and grounded through those contacts, you should have 4.5 volts on the coil ignition supply terminal. Don't test it with the contacts open as there is no load on the resistor so your reading in that case would be around 6 volts. Regards, Kevin.

[Big_Guys_baby]

Sponsored Links (Register now to hide all advertisements)

Gotcha, That helps. I think I def have a voltage drop somewhere. Either the resistor or ignition switch.

[George/Maine]

By keeping the under dash resister you are dropping about 1.5 volts
.5 ohms x 3 amps.
Ford is the only one that's uses a resister with 6 volts with there own FORD coils.
The IC7 needs NO resister.
If you want to check voltage with key ON
Not hooked up to coil should read battery voltage 6 +volts.
Now just hookup to coil and put the meter away.

[Big_Guys_baby]

On IC 7,should the wire from ignition go to the neg terminal and wire todistributor go to pos terminal?

[George/Maine]

Look at what it says on coil pos, bat, ign dist
Its for pos + ground

[BUBBAS IGNITION]

Just a note on coil polarity .
On a new coil it really doesnt matter , HOWEVER once the coil has been ran for a period of time the center core will develop a polarity. Once these laminitated sections become magnetized then the coil needs to be ran in that direction.

I read a service bulliten once that said the coil lost approx 80% of its output when ran the other direction.
Different oems have produced cars with incorrectly applied polaritys and the usual problem was short tune up life etc .

[Mike51Merc]

Originally Posted by BUBBAS IGNITION

Just a note on coil polarity .
On a new coil it really doesnt matter , HOWEVER once the coil has been ran for a period of time the center core will develop a polarity. Once these laminitated sections become magnetized then the coil needs to be ran in that direction.

I read a service bulliten once that said the coil lost approx 80% of its output when ran the other direction.
Different oems have produced cars with incorrectly applied polaritys and the usual problem was short tune up life etc .

Bubba,

Doesn't coil polarity determine the direction of the spark at the plug, usually seen by "the pencil test"?

[V8COOPMAN]

Mike...I'm gonna open my big mouth and suggest that whichever post (POS or NEG) of the battery is grounded determines direction of spark at plug. DD

[Mike51Merc]

Originally Posted by V8COOPMAN

Mike...I'm gonna open my big mouth and suggest that whichever post (POS or NEG) of the battery is grounded determines direction of spark at plug. DD

The spark voltage is created by induction, not a direct connection, so it exists independently from battery polarity.

Battery polarity means less than you'd ordinarily think. Whether the battery is wired positive or negative ground, if the coil is properly wired, it will still send its spark out from the center electrode of the plug and if it's backwards will send the spark from the outer electrode to the center. At least that's what I understand and was seeking confirmation from Bubba.

I kind of remember that the coil polarity determines whether the magnetic field collapses from top to bottom, or bottom to top--- and the direction of the collapse determines the high voltage polarity.

[V8COOPMAN]

Originally Posted by Mike51Merc

The spark voltage is created by induction, not a direct connection, so it exists independently from battery polarity.

Battery polarity means less than you'd ordinarily think. Whether the battery is wired positive or negative ground, if the coil is properly wired, it will still send its spark out from the center electrode of the plug and if it's backwards will send the spark from the outer electrode to the center. At least that's what I understand and was seeking confirmation from Bubba.

I kind of remember that the coil polarity determines whether the magnetic field collapses from top to bottom, or bottom to top--- and the direction of the collapse determines the high voltage polarity.

Mike...Sometimes, when a guy (ME) has heard half of a story for umpteen years and finally gets a hint (from YOU) to go find the rest of the story (GOOGLE), the original guy (ME again) finds he's kinda full of it sometimes. Doing a little research indicates that you're seemingly correct in that the coil determines the direction of spark at the plug...and I wuz wrong. Hate when that happens. Sorry Mike! Pretty good explanation if anyone wants to click the link below. DD

http://mgaguru.com/mgtech/ignition/ig104.htm

[BUBBAS IGNITION]

Originally Posted by Mike51Merc

Bubba,

Doesn't coil polarity determine the direction of the spark at the plug, usually seen by "the pencil test"?

Yes but it doesnt really matter at the spark plug. Vertex mags have always fired 4 in one polarity and the other 4 in another polarity.

Late dis ignitions do the same thing , the plug doesnt care but the coil must remain one way or the other once ran........

[BUBBAS IGNITION]

Originally Posted by V8COOPMAN

Mike...I'm gonna open my big mouth and suggest that whichever post (POS or NEG) of the battery is grounded determines direction of spark at plug. DD

Yep .......

[V8COOPMAN]

Originally Posted by BUBBAS IGNITION

Yep .......

"Yep"...I opened my big mouth, OR, "Yep"...I'm correct?

NOW I'm confused! DD

[scooder]

Ordinary old points and coil ignitions can be tested for coil wired properly (polarity wise with a used coil) with the pencil spark flare test. If it's arse about face you loose tween 60 and 80% of the available coil power.
Martin.

[Big_Guys_baby]

Tons of great discussion on this thread, thanks!

The serious voltage drop was happening at the ignition switch. Was able to hook up an
NOS switch body from carpenters and now showing little at all voltage drop compared to the over 2 volts from before. Also replaced the starter to solenoid cable with 6v correct as opposed to 12 volt skinny cable that had been on forever.

Showing now 6.2 volts at battery and 3.0 volts at coil with under dash resistor still running. the coil on the car is total mystery, but modern style. Tomorrow I am going to by pass resistor and put on IC7 to see how she runs, and more importantly hot starts.

[Graeme / New Zealand]

I've just recently run a fulltime bypass wire with a diode in line on my car and I am amazed at the difference in starting...more punch.

GB