Coil input information

**Surcouf** · 06-01-2020, 08:25 AM

So, without the proper tools, hard to do a good job. I have a rather cheap multimeter; not the dirt cheap one, but not a Fluke neither... So I cannot go below 1 ohm precision. But my coil is showing as a 4.? ohm. I am going to treat myself with a proper Fluke multimeter, unless you guys have a recommendation for another serious multimeter

Now on the voltage: running with moderate rpm, batteries fully charged, alternator excited, I read:
- alternator pos to ground: 14.5V
- coil pos to ground 14.4V
- voltage between coil positive and negative: 6.6V

So questions:
- on my coil negative, I only have the Electronic ignition wire. Is that normal? Should the coil negative be wired to ground? ((Neil's drawing show no ground on his E-3))
- is having a 4 ohm coil mean that I do not need to install that resistor on the positive wire to the coil?

Thank you !!

**ndutton** · 06-01-2020, 08:40 AM

Most importantly and capitalized for emphasis, THE NEGATIVE POST ON THE COIL IS NOT A GROUND AND SHOULD NOT, NEVER, EVER BE CONNECTED TO A GROUND!!!

It is a switched ground directly from the points or EI. When switched on the coil charges up (and heats up), at the instant it is switched off the induced charge stored inside the coil is dumped. The only wires attached to the - post are from the points/EI and if you have one, possibly a tachometer trigger. That's it, nothing else.

At 4.x ohms for the coil and 14.3 V input your current is no greater than 3.75 amps, well under the 4 amp maximum so you're good to go without additional resistance.

**Surcouf** · 06-01-2020, 08:48 AM

Originally posted by ndutton View Post

Most importantly and capitalized for emphasis, THE NEGATIVE POST ON THE COIL IS NOT A GROUND AND SHOULD NOT, NEVER, EVER BE CONNECTED TO A GROUND!!!

It is a switched ground directly from the points or EI. When switched on the coil charges up (and heats up), at the instant it is switched off the induced charge stored inside the coil is dumped.

Sometimes I wonder how I can even ask that question! as soon as I read your explanation, my brain finally switches to what the old point system actually does, and how a negative coil wired to ground would just defeat the whole purpose. This was a hell of a stupid question

Thank you Neil!

**ndutton** · 06-01-2020, 08:55 AM

Originally posted by Surcouf View Post

This was a hell of a stupid question

Not at all. For some reason ignition seems to be the most confusing, confounding, perplexing and intimidating system on our engine and your question provides an opportunity to reiterate its function for others who read this thread now and in the future.

No worries whatsoever.

By the way, I'm particularly enamored with an Ames tester from Harbor Freight Tools. It has all the normal functions and impressive accuracy but also is one of the few that measures DC amps via a Gauss clamp. At $90.00 it gives a lot of bang for the buck.

CM610A 600A T-RMS AC/DC Clamp Meter

https://www.harborfreight.com/cm610a-600a-t-rms-acdc-clamp-meter-64015.html

Amazing deals on this 600 A T-Rms Ac/Dc Clamp Meter at Harbor Freight. Quality tools & low prices.