Groundless

[rodo]

I've lost track of one of my ground wires and need help. This is a long one, is bolted to the back (firewall side) of the head (passenger side) on one end and...uh...that's what I need the help with. What's the other end? Wire must be foot and a half long so lots of choices. Has a ring fitting so it goes on a bolt...somewhere... Car is an '81 with FI. Thanks.

[18Fiatsandcounting]

If it's truly a ground wire, the loose end would work fine attached anywhere in the engine bay where you can find bare metal on the body (bare meaning no paint). Could you describe the connection to the engine a bit more? Connected to the cylinder head itself, to the cam housings, or ? Is the loose wire the typical thickness of 16 or 18 gauge or so, or thicker?

Maybe someone with an '81 spider will recognize your loose wire.

-Bryan

[rodo]

Thanks, 18FIATS.

This is what is confusing to me: on the engine end it is bolted to the head, on a bolt that faces the firewall. The other end, also a ring fitting, I took off of something I cannot remember. When bolting bits back together I assumed the wire needed to be grounded but then I followed the wire and discovered it was bolted to the head. This is what I found confusing. Does the engine require a ground?

[rodo]

And, yes: 14 gauge black wire.

[aj81spider]

The engine does require a ground.

[18Fiatsandcounting]

Yes, the engine does require a ground, and the most important one is the ground for the starter, which draws some 200 amps or so. 14 gauge wire won't handle 200 amps (for very long), so you should have a ground somewhere from the engine block to the body (usually this is a thick wire underneath the car from the area around the starter motor to the body).

But, for your 14 gauge black wire, I could think that this could be connected to any bright shiny spot on the metal chassis (body).

-Bryan

[rodo]

Thanks, all. Looks like a good spot behind one of the bolts for the coil mount will do. I'll let you all know if the car explodes upon starting.

[RRoller123]

I added a heavy battery ground wire, pre-assembled, about 6AWG, I think, between the unused mounting studs for an AC unit on the block, and a ground point near the coil on the fender wall. Bought for thin money at Auto-Zone, etc. I seem to remember about 18 or 24" was fine.

[spider2081]

There is a ground wire for the ignition coil/control module heat sink that connects to the aft bolt holding the bracket to the fender well. Its other end is usually connected by one of the 3 small bolts that attach the rear cam cover to the cam box. I believe the wires prpose is to assure the coil pack ground is at same potential as the distributor's ground This wire is black and about a #14 gauge. Could this be the wire you are talking about??

[18Fiatsandcounting]

There is a ground wire for the ignition coil/control module heat sink that connects to the aft bolt holding the bracket to the fender well. Its other end is usually connected by one of the 3 small bolts that attach the rear cam cover to the cam box. I believe the wires prpose is to assure the coil pack ground is at same potential as the distributor's ground This wire is black and about a #14 gauge. Could this be the wire you are talking about??

This makes a lot of sense and is likely the answer. While the lights and gauges and ignition points of older cars may not care if you have differences in the ground potential of tens or even hundreds of millivolts across various points on the car body, transistorized ignition circuits may be sensitive to such differences and thus require that their ground wire (and thus ground potential) be as close to the distributor as possible.

-Bryan

[rodo]

That has got to be the wire. it is bolted to the rear cam cover. No doubt electronics is not my strong point, but how does that ground the heatsink? Or more to the point, why does a heatsink require a ground? or, how is the coil pack ground at the same potential as the distributor's ground? What from the coil goes through that wire if it is bolted to the fender? Sorry if I'm not following correctly.

[spider2081]

why does a heatsink require a ground?

In this case the ignition control module is mounted to the heat sink under the ignition coil. The ignition control module require a good electrical ground for it to operate properly. One of the screws holding the ignition control module to the heat sink completes the electrical ground to the heat sink. The heat sink is then held to it's mounting bracket by studs on the mounting bracket. Neither of these parts are painted. The coil pack mounting bracket is held to the passenger side fender well by 3 bolts. The fender well is a painted surface so to be sure there is a good ground the additional wire is used.

how is the coil pack ground at the same potential as the distributor's ground?

Using the black wire connecting the engine to the coil pack mound give the assurance both should be at the same potential.

What from the coil goes through that wire if it is bolted to the fender?

I don't think the Magneti Mareilli coil needs a ground to function. It is the ignition control module that need a ground to operate and they are both mounted to the heat sink.
Ignition points supply a ground to the ignition coil when the points are closed. The ignition control module is an electronic circuit that acts like a set of points. In order to supply a ground to the coils minus terminal it has to have a ground itself. Points in a distributor get their ground through the distributors physical mounting into the engine.

[rodo]

Thanks for that, Spider2018. I should have remembered that from when I took the module off!

Another step accomplished!