Pertronix wiring

[elancoupe]

I am soon going to install a positive ground Pertronix Ignitor and coil. I did quite a bit of archives reading on this, and had a pretty good idea of how to.......until I got a hold of the Pertronix wiring diagram.

I had read, that in order to continue with proper tach operation, a separate power lead needed to be run to the unit itself. Below is attached a photo of the diagram, the instructions say "the black/white ignitor wire and the 20AWG ground wire should be the only wires connected to the coil"

I am a bit wiring challenged, a bit of enlightenment would be appreciated.

[billwill]

Is your car wired POSITIVE Earth or is it NEGATIVE Earth?

i.e which cable on the battery is bolted to the chassis.

[elancoupe]

I am soon going to install a positive ground Pertronix Ignitor and coil. .

The car is positive ground, or earth, depending on your location.

[rgwitherell]

I am installing a negative ground pertonix on an S2 which I have converted to negative ground.

I have attached ( I hope) the Pertronix diagram for negative ground.

With the orginal points system, whether it is positive or negative ground, the connection from the ignition switch to the coil goes through the the loop in the tachometer and the connection between the coil and the ground goes through distributor points. In the positive ground case the positive side of the coil is switched on and off by the points and the negative side in the negative ground case. (Note that if you change from positive to negative ground you should reverse the connections to the coil) In either case the tachometer sees a full on/off switching of the current flowing through the loop.

Both designs of Pertonix, on the other hand, appear to switch on and off only the negative side of the coil, i.e the ignition switch side for positive ground installations and the ground side for the negative ground type. I assume the ignitor, unlike points, requires a continuous power supply for it to work. The case of the ignitor is grounded to the distributor base plate and in both diagrams it appears the continuous flow is from the ignition switch through the ignitor to the distributor base plate. If the tachometer loop is left in the connection from the ignition switch, it will only see a partial change in current as the coil is switched on and off. As some have suggested with either type of Pertonix, the tachometer connection should be in the wire between the ignitor and the negative terminal of the the coil so that it sees a full on/off switching of the current.[attachment=0]Pertronix Negative Ground1.jpg[/attachment

[stugilmour]

I am installing a negative ground Pertronix on an S2 which I have converted to negative ground.

As some have suggested with either type of Pertronix, the tachometer connection should be in the wire between the ignitor and the negative terminal of the the coil so that it sees a full on/off switching of the current.[attachment=0]Pertronix Negative Ground1.jpg[/attachment

rgwitherell

I installed the negative ground Pertronix in my Plus 2 recently; the model I have is the complete replacement distributor type and uses the same diagram as you have posted. The tach loop wire is from the ignition switch, through the loop bridge, and to the positive terminal of the coil, just like in the diagram. This is completely consistent with the stock points wiring in my car. The only modification from stock is my 'loop' runs straight through the bridge; this modification is taken from a recommendation in my Plus 2 Workshop Manual for a high output coil.

The issue of the tach reading jumping around with various types of electronic ignition has had several posts. The key point is to power the Pertronix unit (the Pertronix red power wire in the negative ground set-up) from a separate hot in run and start location, rather than from the coil positive terminal as shown in the Pertronix negative ground diagram. The issue apparently is that the power wire connected to the positive coil terminal damps the pulses that the tach sees, distorting the reading. I accomplished this with a separate wire directly from the ignition switch; an alternative is to find a suitable connection at the fuse box under the hood. Mine works fine, and I was able to adjust the tach readings to a clip on tuning tach with the trimming screw inside the tach case.

elancoupe, I have looked over the positive earth diagram before, and don't quite get it as the wire colours seem a bit bizarre. Another list member (Bill on Vancouver Island) and I were corresponding regarding how to get his to read the tach correctly in his positive earth car with Pertronix. Not sure how he exactly wired his, but it works except for the tach readings hopping around.

Anyway, my guess after looking it over again and reading over rgwitherell's excellent post is that the black/white wire in your diagram has to go through the tach loop; this is consistent with what rgwitherell is recommending in his post above. How one does this depends on your existing wiring and tach, but I think the easiest is to run a new wire loop from the Pertronix through the firewall, through the tach loop, and back to the negative terminal of the coil.

The other trick is to recognize the Pertronix black wire in the Positive Earth diagram as the unit power wire. I believe this one could be supplied with your existing negative coil terminal wire after removing it from the tach loop bridge and from the coil. This is essentially coming straight from the igintion switch, perhaps picking up the instument power / voltage stabilizer along the way.

Open to correction on my description & recommendation as I do not have a positive earth car and the wiring details vary a lot between models.

HTH

[paddy]

Just to be absolutely sure before going any further, check we are talking about the right sort of tach. The replies so far assume that yours says "RVI Positive earth" on the face.

Paddy

[elancoupe]

Just to be absolutely sure before going any further, check we are talking about the right sort of tach. The replies so far assume that yours says "RVI Positive earth" on the face.

Paddy

We are indeed talking about a postive earth rvi tach.

What I have read about this unit are in agreement with the above posters, in that the unit tiself needs to be powered by a separate source, without the tach in the loop. You could run a new wire to the Pertronix black wire, from the ignition switch, bypassing the tach loop, no problem. The question then would be, how to wire the tach.

[paddy]

The question then would be, how to wire the tach.

The RVI loop has to be in series with the coil, and nothing else. In principle, this could be on either side of the coil.

Instead of connecting the coil +ve terminal directly to earth, couldn't you connect that to the tach, and ground the other end of the loop?

Paddy

[elancoupe]

The question then would be, how to wire the tach.

The RVI loop has to be in series with the coil, and nothing else. In principle, this could be on either side of the coil.

Instead of connecting the coil +ve terminal directly to earth, couldn't you connect that to the tach, and ground the other end of the loop?

Paddy

This seems logical/reasonable. Unless somebody can offer a better alternative, I will give this a try. I sent the dizzy to Advance Ditributors for rebuild/recurve, should have it back shortly.

[stugilmour]

The question then would be, how to wire the tach.

The RVI loop has to be in series with the coil, and nothing else. In principle, this could be on either side of the coil.

Instead of connecting the coil +ve terminal directly to earth, couldn't you connect that to the tach, and ground the other end of the loop?

Paddy

This seems logical/reasonable. Unless somebody can offer a better alternative, I will give this a try. I sent the dizzy to Advance Ditributors for rebuild/recurve, should have it back shortly.

Seems to make sense to me as well Paddy. I will mail the thread link to Bill to see if this has been tried on his car.

[elancoupe]

[
. I will mail the thread link to Bill to see if this has been tried on his car.

Thanks, Stu.

[Emma-Knight]

Does a coil have a true + - system? I thought its just a kind of transformer that wouldn't know current direction - but does have a true supply side (sw (switched / feed) and cb (contact breaker).

Anna

[john.p.clegg]

Anna

You are correct,but when it comes to the high voltage spark end,it does matter if the spark travels from the central electrode to the outer rim or vice versa..(hence polarity of low voltage wiring)

John

[bob_rich]

HI

I think if the coil +ve terminal goes to the battery +ve be it ground or the actual live switched terminal if a -ve earth car then the spark will be the correct polarity. Polarity does effect the break over voltage and spark plug gap erosion slightly. These days though where a lot of cars used wasted spark ( one spark of each polarity is generated fed to a pair of plugs so one plug is +ve the other -ve) provided there is enough energy then there should not be a problems. On the primary side of the coil where the coil lead goes through the tacho loop it has to be the correct way around else tacho may not work.

hope this helps best of luck

Bob

[elancoupe]

Ok, to follow up on this..... I fitted the revamped dizzy and ignition this morning. I wired the unit up exactly as per the Pertonix diagram , with the tach in its' original postion in the ignition wire. I wasn't sure how to static time this ignition, and didn't want to do anything to fry it. I was able to dig in the archives here, and find how to static time a Pertronix quickly and easily.

Anyway, I got the car running and timed with a light. Not only does it run sweetly, but the tach works at least as well as it did on the old ignition. I highly recommend Advanced Distributors should anyone need a rebuild/recurve, Jeff is fantastic to deal with.

We are in the process of getting 6-8 inches of snow, so road testing is out for now.

Thanks to everyone for their input.