Ignition wiring - help needed

[TrevS]

Hi all

We've been trying to convert my 4.2 S1 E-type to an electronic ignition. We've put the Pertronix unit in but want to double check the wiring is correct with some owners.

Before
We had 2 wires coming from the coil. The B/W wire went to distributor from the positive terminal of the coil. There was also a White wire that came from the positive terminal but we aren't sure where this goes. We think it might be for the ignition switch. Can someone confirm.


After
We now have 3 wires connected to the coil. We have a Red wire from positive coil terminal to the distributor and a Black wire from negative to the distributor. We also have the original White wire that we think goes to the ignition from the negative terminal.


When converting the ignition the instructions for the new system expected there to be a wire from the negative terminal of the coil to the distributor. Instead ours was connected to the positive side of the coil. Why would this be? Is it something the previous owner had connected wrongly?

Finally can someone confirm that our new wiring is correct and that there should be 3 wires connected to the coil?

Thanks

Trev

[Heuer]

Unusual to find a coil marked +ve and -ve these days. They are normally marked CB (contact breaker) and SW (ignition switch). It does not really matter which side goes to which although there is evidence to say there is a performance improvement doing it one way rather than the other but leave that for another day. Notionally you need to connect the white (switched +ve 12v) to the +ve terminal and the red Petronix wire to the same terminal. Black should go to -ve terminal. DO NOT connect it the way you show it in the diagram as you will blow a fuse or damage the Petronix!

e.g.


From the Petronix instructions:

[mgcjag]

Hi Trev....make sure you dont leave the ignition on this can damage the pertronix.....it should tell you in the instructions

[Tbob]

Looks like the fellows have supplied you with good info, but PM me if you have questions - I just did this conversion.

[Heuer]

And once you have it working you can ponder the following:

Coil Polarity
The polarity of the coil should match that of the battery - coil +ve to battery +ve, coil -ve to battery -ve. No matter whether the car is +ve or -ve earth or which way the coil is installed (regardless of coil markings) it will still output voltage. Spark plugs are however more sensitive when it comes to polarity and the coil should be connected to provide negative polarity to the spark plugs centre electrode. It takes 10% less voltage for the plugs to arc if the hotter centre electrode is -ve, and the cooler (by comparison) earthed electrode is +ve. With the terminals reversed and the centre electrode is +ve, the car will still run with but with a 10% voltage handicap and in low temperatures, driving fully loaded and accelerating hard up a hill may misfire. If the coil is modern and has - & + markings connect accordingly. With CB and SW markings there is no way to tell whether the coil is positive or negative earth other than looking up the Lucas serial number. The coil can be tested for polarity using a voltmeter set to its highest range, with the positive (usually red) lead connected to a cylinder head bolt and the negative (black) lead connected to a plug cap - this applies regardless of whether the car is positive or negative earth. Cranking the engine will cause the needle (or digital readout) to swing upwards if the coil is connected correctly. If the needle swings down off the scale (or the digital readout goes negative) the coil is connected wrongly, and the coil leads should be reversed, regardless of markings.

[caveman]

Hi Trev,
Just checked my wiring and it's exactly as David's diagram;

Red Pettronix Wire to + on Coil
White Wire to + on Coil

Black Pertronix Wire to - on Coil

Of note, both my Lucus Sports Coils have - and + terminal markings.
I do have an extra wired terminal connector near the coil that is black and white colour wiring. It's taped to the side of the coil loom and has never been fitted. Modern wiring loom but not sure what it is and as it's never been used I'm not worried about it.
Just been out today for first drive of the year in glorious sunshine and it's running like a dream.

[mgcjag]

Hi Steve..that Bk/wh is probably the original wire pre your Pertronix from tbe coil to dizzy the other end may be near the dizzy

[caveman]

Hi Steve,
Your bang on the money!
I've just been under the bonnet cleaning up after today's run and I found the corresponding end taped up at the dizzy. I then remembered taping these up when I fitted said Pertronix some years ago! I can sleep easy tonight, now, which way is the bedroom . Thanks.

[64etype]

Just an aside comment...after looking at the Pertronix wiring diagram, I was surprised how easy the device would be for a thief to hot wire the ignition....one jumper wire. The Crane/Allison with optical trigger has at least three different ways to completely disable it with hidden switches. To get my car started, a thief would have to find two or three remote switches, or install a set of points (or a Pertronix). No way to quickly bypass the ignition switch. In fact I might have to study the wiring diagram to get it going after a couple of beers at the local saloon.

[cactusman]

When it comes to it the same would apply to points.....simply connect the coil to the battery! Trick is to remove the ability to operate the starter motor using a switch or other suitable isolation device or better still sabotage the power to the fuel pump and apply a very substantial lock to the steering wheel.

Of course you could also whip off the rotor arm too....

[64etype]

When it comes to it the same would apply to points.....simply connect the coil to the battery! Trick is to remove the ability to operate the starter motor using a switch or other suitable isolation device or better still sabotage the power to the fuel pump and apply a very substantial lock to the steering wheel.

Of course you could also whip off the rotor arm too....

Quite right. Either points or Pertronix are easy pickins in the ignition hot wire department. I don't need to isolate the starter because I can easily make the ignition certifiably comatose with little chance for revival without an extended search or a complete distributer replacement. A starter kill is as easy to defeat as a points/Pertronix ignition. I do have a fuel pump kill, though.

[mark10337]

I can confirm also.

White wire (from Rev counter on a S2) to +
Red wire from Petronix to +
Black wire to -

black and white wire that was there is now redundant.

Interestingly the wiring diagram from Coventry shows the white wire from the Rev counter to the -ve terminal on the coil. This had me stumped for a day when I redid the wiring. If it hadn't been for that, when I changed the engine bay loom it would have been perfect first time.

[TrevS]

Hi all

Just wanted to say thanks to everyone for the wiring info. I finally got round to testing everything and the car is running like a dream.

Due it's MOT now so hoping to get that sorted this week and get back enjoying the car

Trev