The Ford Barn

40cpe · 10-06-2011, 02:07 PM

This isn't exactly an early V8 question, but you guys know the answer. I have a points distributor with a coil fed through a resistor. The coil has "12V External Resistor Required" printed on it. The resistor has 4.8V on the load side and feeds to the (-) side of the coil, the (+) side is run to the distributor. I bought the car this way and it started running poorly so I checked the distributor inside. The points are discolored half way back on the arm like it has been hot. The electrical is 12V negative ground charged by a one-wire alternator. I thought the coil should be connected (+) to the hot wire, (-) to the distributor on negative ground systems. Would reversed polarity cause the burned points? If not, what should I look for? Thanks in advance, Gene

BUBBAS IGNITION · 10-06-2011, 06:38 PM

Quote:

Originally Posted by 40cpe

This isn't exactly an early V8 question, but you guys know the answer. I have a points distributor with a coil fed through a resistor. The coil has "12V External Resistor Required" printed on it. The resistor has 4.8V on the load side and feeds to the (-) side of the coil, the (+) side is run to the distributor. I bought the car this way and it started running poorly so I checked the distributor inside. The points are discolored half way back on the arm like it has been hot. The electrical is 12V negative ground charged by a one-wire alternator. I thought the coil should be connected (+) to the hot wire, (-) to the distributor on negative ground systems. Would reversed polarity cause the burned points? If not, what should I look for? Thanks in advance, Gene

Sounds like the ignition is wired for a pos ground vehicle.
The coil needs to be of correct polarity and sounds like it needs to be a negative ground coil.
If the coil is ran incorrect it will take a polarity set and wont perform when wired the other way.
My suggestion is start all over with a good quality coil, new (proper 1.5 ohm) resistor and replace the points with a good quality set of contacts......

40cpe · 10-06-2011, 07:26 PM

Bubba, you sure know your stuff! I replaced the points with some from a spare distributor, reversed the polarity on the coil (which appeared new) and was running the engine setting the dwell and it died like the switch was cut off. After checking all my wiring and continuity the coil wasn't firing. I replaced the coil with a spare and the engine fired up. I didn't expect that reversing the polarity would kill the coil.

What do you think heated the points? Maybe they were run without a resister, who knows.

Since I need to start all over with new stuff, what is your opinion of the Pertronix ignition and coil?

ford1 · 10-06-2011, 09:31 PM

if the points were discolored that far up the shaft i would think the key was left on at some point,if your running 12v i would buy an internaly resisted coil, get rid of the resistor, i would stay with the points, at least you can buy parts at most auto parts stores if some thing goes wrong

40cpe · 10-06-2011, 10:28 PM

I've been running a Pertronix in my '40 for 16 years. When I first installed it I used my existing coil and some years later it failed and burned up the Pertronix. I carried points and condenser with me, installed them, and went on my way. I bought another unit not knowing the coil was at fault and promptly burned the new one up. When I finally discovered it was the coil at fault I bought a their Flame Thrower coil and they replaced the Pertronix free. The tech line was very helpful through the process. The company and the product have my respect.

31chevy · 10-07-2011, 07:12 AM

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Please correct me if i'm wrong. If the vehicle is neg. grnd then the neg. side of the coil goes to distributor. If vehicle is + grnd the + side of coil goes to distributor. Murphy's law seems to let me do things wrong. This info is for a friend of mine with 32 chev.
Gary. Thank you.

tdlmomowers · 10-07-2011, 07:24 AM

Quote:

Originally Posted by 31chevy

Please correct me if i'm wrong. If the vehicle is neg. grnd then the neg. side of the coil goes to distributor. If vehicle is + grnd the + side of coil goes to distributor. Murphy's law seems to let me do things wrong. This info is for a friend of mine with 32 chev.
Gary. Thank you.

This is correct, On pos. ground, the pos. side of the coil goes to the dist. On Neg. ground, the neg. side of coil goes to the dist. Try finding a coil that has built in resistance, it will get rid of your external resistor. Go to NAPA and tell the counterman what you need and hopefully they can help you find a coil.

BUBBAS IGNITION · 10-07-2011, 07:25 AM

Quote:

Originally Posted by 31chevy

Please correct me if i'm wrong. If the vehicle is neg. grnd then the neg. side of the coil goes to distributor. If vehicle is + grnd the + side of coil goes to distributor. Murphy's law seems to let me do things wrong. This info is for a friend of mine with 32 chev.
Gary. Thank you.

Correct.......

40cpe · 10-07-2011, 07:25 AM

Quote:

Originally Posted by 31chevy

Please correct me if i'm wrong. If the vehicle is neg. grnd then the neg. side of the coil goes to distributor. If vehicle is + grnd the + side of coil goes to distributor. Murphy's law seems to let me do things wrong. This info is for a friend of mine with 32 chev.
Gary. Thank you.

You are correct

31chevy · 10-08-2011, 07:16 AM

Thank all of you for the info.
Gary.

Bruce in southern OH · 10-08-2011, 03:26 PM

Take a look at this, Bruce

Coil Polarity

I was converting my older British car over from positive to negative ground when I came across the question of coil polarity. I discovered coil polarity is very much misunderstood. In researching it, I was very confused until I found out there are two definitions of coil polarity. I talked to three or four knowledgeable people on the subject and read several technical books and articles. Everything made sense in itself but didn't jive together until I found out they were talking apples and oranges.

Definition #l Coil Polarity (In relation to battery)

The polarity of the coil should match that of the battery by connecting it so (+) goes to (+) and (-) connects to (-). But don't worry about which way you install the battery (positive or negative ground) or which way you install the coil (regardless of coil markings) it will automatically adjust itself. The coil will work efficiently and put out the same voltage either way it is hooked up, but the spark plugs are more sensitive when it comes to polarity, hence our second and more important definition.

Definition #2 Coil Polarity (In relation to spark plugs)

Coil polarity should be such so as to provide negative polarity to the spark plugs center electrode.

It has been found that it takes approximately 15% less voltage to form an arc at the plugs, if the hotter center electrode is negative, and the cooler (by comparison) ground electrode is positive. The center electrode is hotter since heat transfer from the tip must make its way through the porcelain insulator past the sealing gaskets to the shell block and then to the water jackets.

If your center electrode is positive, your car will probably still run fine until, with its 15% handicap, it exceeds the coil output. If you live where temperatures dip down to 0° you may not get your car started. Driving with a full load and accelerating hard up a hill may cause an ignition miss. If your ignition system is well worn to where you have various voltage losses, you could get a miss.

Correct coil polarity won't eliminate these problems, just put them off by 15%.

If your coil has - & + markings by the primary terminals, you will be pretty safe by hooking it up by those marks, but test it for correct polarity anyway, using one of the tests listed further on. If your coil has CB & SW or BAT & DIST markings, there is no way of telling if the coil was marked in relation to a positive or negative ground car, and the only sure way to tell if the coil is installed right is to test it out.

You test for correct polarity by hooking up a voltmeter with the negative lead to the plug terminal (which should be of negative polarity) and the positive lead to the block (which should be of positive polarity). Set the meter on the highest volt range. These connections remain the same whether you have a positive ground or negative ground electrical system. The secondary winding's polarity which we are testing is determined by the combined hookup of the battery and primary windings, so it may or may not match the battery's ground.

Cranking the engine over (you don't have to start it) should show an upward swing of the voltmeter needle (don't be concerned with taking a reading). If the needle swings down off the scale, your coil is hooked up wrong. To correct, reverse coil primary leads. Do not worry about the coil markings (refer to definition #1).

If you don't have a voltmeter, test by removing a plug wire from a plug and hold a plain lead pencil point in the path of the arc. A flair (hard to see) towards the plug shows correct polarity while a flair towards the coil shows reversed polarity.

Back to General Tech Tips

10-06-2011, 07:26 PM	#3
40cpe Senior Member Join Date: May 2010 Location: Star, MS Posts: 4,028	Re: overheated points Bubba, you sure know your stuff! I replaced the points with some from a spare distributor, reversed the polarity on the coil (which appeared new) and was running the engine setting the dwell and it died like the switch was cut off. After checking all my wiring and continuity the coil wasn't firing. I replaced the coil with a spare and the engine fired up. I didn't expect that reversing the polarity would kill the coil. What do you think heated the points? Maybe they were run without a resister, who knows. Since I need to start all over with new stuff, what is your opinion of the Pertronix ignition and coil?

10-06-2011, 09:31 PM	#4
ford1 Senior Member Join Date: May 2010 Location: oroville ca. Posts: 1,554	Re: overheated points if the points were discolored that far up the shaft i would think the key was left on at some point,if your running 12v i would buy an internaly resisted coil, get rid of the resistor, i would stay with the points, at least you can buy parts at most auto parts stores if some thing goes wrong

10-06-2011, 10:28 PM	#5
40cpe Senior Member Join Date: May 2010 Location: Star, MS Posts: 4,028	Re: overheated points I've been running a Pertronix in my '40 for 16 years. When I first installed it I used my existing coil and some years later it failed and burned up the Pertronix. I carried points and condenser with me, installed them, and went on my way. I bought another unit not knowing the coil was at fault and promptly burned the new one up. When I finally discovered it was the coil at fault I bought a their Flame Thrower coil and they replaced the Pertronix free. The tech line was very helpful through the process. The company and the product have my respect.

10-07-2011, 07:12 AM	#6
31chevy Senior Member Join Date: May 2010 Location: Lake City Mi. Posts: 807	Re: overheated points Sponsored Links (Register now to hide all advertisements) Please correct me if i'm wrong. If the vehicle is neg. grnd then the neg. side of the coil goes to distributor. If vehicle is + grnd the + side of coil goes to distributor. Murphy's law seems to let me do things wrong. This info is for a friend of mine with 32 chev. Gary. Thank you.

10-08-2011, 07:16 AM	#10
31chevy Senior Member Join Date: May 2010 Location: Lake City Mi. Posts: 807	Re: overheated points Thank all of you for the info. Gary.

10-06-2011, 02:07 PM	#1
40cpe Senior Member Join Date: May 2010 Location: Star, MS Posts: 4,028	overheated points This isn't exactly an early V8 question, but you guys know the answer. I have a points distributor with a coil fed through a resistor. The coil has "12V External Resistor Required" printed on it. The resistor has 4.8V on the load side and feeds to the (-) side of the coil, the (+) side is run to the distributor. I bought the car this way and it started running poorly so I checked the distributor inside. The points are discolored half way back on the arm like it has been hot. The electrical is 12V negative ground charged by a one-wire alternator. I thought the coil should be connected (+) to the hot wire, (-) to the distributor on negative ground systems. Would reversed polarity cause the burned points? If not, what should I look for? Thanks in advance, Gene

10-08-2011, 03:26 PM	#11
Bruce in southern OH Senior Member Join Date: May 2010 Location: Proctorville Posts: 1,584	Re: overheated points Take a look at this, Bruce Coil Polarity I was converting my older British car over from positive to negative ground when I came across the question of coil polarity. I discovered coil polarity is very much misunderstood. In researching it, I was very confused until I found out there are two definitions of coil polarity. I talked to three or four knowledgeable people on the subject and read several technical books and articles. Everything made sense in itself but didn't jive together until I found out they were talking apples and oranges. Definition #l Coil Polarity (In relation to battery) The polarity of the coil should match that of the battery by connecting it so (+) goes to (+) and (-) connects to (-). But don't worry about which way you install the battery (positive or negative ground) or which way you install the coil (regardless of coil markings) it will automatically adjust itself. The coil will work efficiently and put out the same voltage either way it is hooked up, but the spark plugs are more sensitive when it comes to polarity, hence our second and more important definition. Definition #2 Coil Polarity (In relation to spark plugs) Coil polarity should be such so as to provide negative polarity to the spark plugs center electrode. It has been found that it takes approximately 15% less voltage to form an arc at the plugs, if the hotter center electrode is negative, and the cooler (by comparison) ground electrode is positive. The center electrode is hotter since heat transfer from the tip must make its way through the porcelain insulator past the sealing gaskets to the shell block and then to the water jackets. If your center electrode is positive, your car will probably still run fine until, with its 15% handicap, it exceeds the coil output. If you live where temperatures dip down to 0° you may not get your car started. Driving with a full load and accelerating hard up a hill may cause an ignition miss. If your ignition system is well worn to where you have various voltage losses, you could get a miss. Correct coil polarity won't eliminate these problems, just put them off by 15%. If your coil has - & + markings by the primary terminals, you will be pretty safe by hooking it up by those marks, but test it for correct polarity anyway, using one of the tests listed further on. If your coil has CB & SW or BAT & DIST markings, there is no way of telling if the coil was marked in relation to a positive or negative ground car, and the only sure way to tell if the coil is installed right is to test it out. You test for correct polarity by hooking up a voltmeter with the negative lead to the plug terminal (which should be of negative polarity) and the positive lead to the block (which should be of positive polarity). Set the meter on the highest volt range. These connections remain the same whether you have a positive ground or negative ground electrical system. The secondary winding's polarity which we are testing is determined by the combined hookup of the battery and primary windings, so it may or may not match the battery's ground. Cranking the engine over (you don't have to start it) should show an upward swing of the voltmeter needle (don't be concerned with taking a reading). If the needle swings down off the scale, your coil is hooked up wrong. To correct, reverse coil primary leads. Do not worry about the coil markings (refer to definition #1). If you don't have a voltmeter, test by removing a plug wire from a plug and hold a plain lead pencil point in the path of the arc. A flair (hard to see) towards the plug shows correct polarity while a flair towards the coil shows reversed polarity. Back to General Tech Tips