Tag: ignition coil

Tech Tip: Ignition Coil Polarity Check on Early Model Vehicles – Randy Rundle @Underhood Service

Tech Tip: Ignition Coil Polarity Check on Early Model Vehicles – Randy Rundle @Underhood Service

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Rundle’s Rules: Ignition Coil Polarity Check

Prior to 1956, the year when most all of the domestic auto manufacturers upgraded to 12-volt electrical systems using standardized negative ground designs, some of the electrical systems on cars and trucks were positive ground and some were negative ground.

Ford used positive ground, while General Motors used both.

Chevy trucks were negative ground, while GMC trucks used positive ground. There was and still is a lot of confusion concerning the polarity of electrical systems and how to properly connect the ignition coils, as well as the battery.

On classic and antique vehicles, you can test for correct polarity of the ignition coil by using a voltmeter.

Connect the negative lead to the (-) negative terminal and the positive lead to the engine block.
Set the meter on the highest volt range (these connections are the same whether you have a positive ground or negative ground electrical system).

The secondary winding’s polarity, which you are testing, is determined by the combined hookup of the battery and primary windings.

Crank the engine over (do not start it) and the needle of the voltmeter should show an upward swing to the plus or positive side (don’t worry about taking a reading).

If the needle swings down to the negative side and gives a negative reading, your coil is hooked up backward. To correct the polarity, simply reverse the coil primary leads.

A coil with reversed polarity will have about a 20% lower output, which may not show up at idle and low rpms, but can cause an engine to miss or stumble under load and at higher engine rpms.

This is why a technician who changes the points, condenser and other electrical components will still detect an engine miss.

The lesson here is, too often, it is “assumed” that the wiring is correct.

— Randy Rundle

Randy Rundle is the owner of Fifth Avenue Antique Auto Parts, Clay Center, KS, and services antique and classic vehicles. An author of six automotive technical books, Rundle has spent 20-plus years solving electrical, cooling and fuel-related problems on all types of antique and classic vehicles.

2000 Chevrolet S10 Xtreme Ignition Coil Change Part 2

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Due to the horrible weather the coil change is taking longer than I’d like, but it’s getting there!

To fit the aftermarket NAPA coil the factory rivets needed to be ground down to facilitate the removal of the old unit

Once removed I tidied the ground areas up and applied some paint to stop things from rusting and make things look a little better.

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2000 Chevrolet S10 Xtreme Ignition Coil Change Part 1

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If you’ve been reading the blog you’ll know that the S10 has been having some breakdown issues which appear to have been corrected by the replacement of the ignition coil. Now the coil I have is an aftermarket unit from NAPA.(kindly bought in the States by a relative :))

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To remove the coil you need to remove the throttle cable bracket and then remove the bracket that contains the coil and the ignition module. As you can see the original coil is riveted to the bracket. The NAPA coil comes with a little fitting kit. To remove the original coil I think the rivets will need to be ground or drilled out.

More next time!

The Chevrolet S10 Xtreme Was Unwell

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About two weeks ago the Chevy started to run a little rough and this had become worse ending up in a couple of breakdowns

I scanned the truck using the WiFi OBDII Wireless Dongle, using the Dash Command app on the Apple iPhone 6 Plus

No codes were found and all the diagnostics looked fine, but the truck would still stall out after about 4 miles and refuse to restart until cooled.

Luckily I had asked a friend to bring back some ignition components during a visit to the States after some previous issues, this meant I was able to swap out the coil.

(You may notice that the coil was made in Poland, so it’s had a long round trip back to Europe!!)

I have driven twelve miles in testing so far and all seems OK, I never like to have “cured” a fault without being 100%

Looks like she’s dead Jim…

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A day after the trauma of the breakdown on the way to Wheels Day, the investigation began!

Still refusing to start and having no spark I decided to swap in a known good coil, lo and behold the car started and I was able to reverse out of the garage having to push in the day before.

After letting the car idle for about 10 mins it decided to cut out and refused to restart.

Knowing that the Pertronix is very sensitive to correct voltage I decided to charge the battery, however the car still failed to start and still had little or no spark.

So the decision to go back to points is confirmed and the parts are on order from O’Neills