Does the coil have a ground wire?

 

I'm guessing it would be grounded through the connector/harness.


...but I'm just curious.

 

It is grounded through the secondary winding (lead from coil to center post on distributor cap) for remote coil and inside the distributor cap for an internal coil.

 

The secondary winding is a long piece of fine wire wrapped around the iron core a couple thousand times. One end is hooked to the terminal for the coil wire, and the other end is connected to the coil frame.

The frame of the coil MUST BE grounded. Otherwise, the spark current will have nowhere to flow. There is not a ground wire as such.

 

Some are going to think that I'm nuts, but there isn't a ground wire for the secondary side (hi-tension) of the coil. The primary side gets +12 volts (ignition) and is grounded by the module to 'charge' the coil. When the module opens the primiary grounding the magnetic field collapes and the coil fires.

The secondary side goes to the same +12v ignition feed as the primary, while the other side of the secondary is the hi-tension lead to the center of the cap (rotor button).

I know it sounds crazy, but the Helm schematics show this along with a DVM showing the same thing.

RBob.

 

No you're not at all crazy, at least not about that. That is correct at least for some coil setups. But not all.

If you think about it carefully, if you were (say) 30,000 volts, ground and 12 volts would both look very much alike to you. The impedance of the 12V source is supposed to be low enough that the actual spark current in the secondary winding is relatively insignificant. And, since the spark is a very high-frequency (short duration) event, it can also easily pass through a capacitor. Which is one good reason to always put a condenser on the + side of your coil even if one didn't come there from the factory.

As shown in the schematic though, for at least some of the divorced-coil HEIs, they used the frame as ground, rather than returning the low end of the secondary winding to 12V.

 

In the first picture I posted, it showed the ground at the secondary winding with another ground at the ignition module to the distributor base. This picture was from a 89 service manual. Here is one from a 92 service manual showing only the ground at the ignition module.

 

I know this is an old post but I was directed here from a recent post about blown ICMs. This post confuses me in the fact that there are half answers and some misinformation. The coil secondary is grounded, but not a conventional ground as you might expect. The secondary side is grounded through the spark plug to engine ground. The high voltage, created in the secondary side of the coil when the primary side breaks down, is great enough to jump the spark plug gap and return to ground through the engine block. I just thought I would expand on the answers above that state the coil secondary is grounded through the distributor center post. This is correct but does not explain the complete path across the plug gap to ground. HTH