Sports Coil polarity

[Philk]

I've recently been enjoying my 3.8 OTS which has finally got onto the road following its professional mechanical recommissioning and subsequent registration in the UK.

Sadly, I've had to ditch my original 1964 coil and, with electronic ignition now built into the distributor, I've fitted an InterMotor sports coil (DLB105). This works perfectly (and the car now runs perfectly). The only question I have is that both the new coil only works if the negative side is connected to the chassis (whereas the instructions point to it requiring an earth from the positive terminal if the car has positive ground). My car has positive ground (something I was keen to keep original when I had the work done on the car). I've spoken to the restorers who've said that, for both my car and others they have worked on, this was the only way they could get the coil to work with the Electronic Ignition (this was fitted into the distributor by a separate specialist company when that was also overhauled).

Does anyone have any thoughts...... as I say, the car is working perfectly, but I am intrigued to understand why the polarity seems to require this when the car is undoubtedly positive earth.

[mgcjag]

Hi Phil....this is worth reading....lots of info out there if you google search ignition coil polarity....what electronic ignition do you have some are some only work on neg eth.....Steve
http://mgaguru.com/mgtech/ignition/ig104.htm

[Philk]

Hi Phil....this is worth reading....lots of info out there if you google search ignition coil polarity....what electronic ignition do you have some are some only work on neg eth.....Steve
http://mgaguru.com/mgtech/ignition/ig104.htm

Hi Steve - thanks for that. I had seen that earlier which reinforced my thought that the car should have its positive terminal going to earth (on a positive ground car). My electronic ignition (as fitted by Distributor Doctor) is a Pertronix Ignitor system for positive earth cars (LU-166AP12). The instructions that came with it is that the +ve coil on the coil should go to earth. This makes me more confused than ever given the car runs extremely roughly if I swap the coil connections over. It should be so straightforward (given the car has had a new harness professionally fitted)! I am just wondering if it is something around how it has been installed in the distributor.

I should finally add that I have checked the coil resistance and it is just under 3 Ohms which, for a six cylinder car, should be fine (I understand)

Best

Phil

[mgcjag]

Hi Phil.....do you have the diagram of the pertronix.......you mention connect +coil to earth which sounds odd..i have a neg eth pertronix..from coil one wire to ignition....and from same terminal to the ignitor....the other coil connection also goes to the ignitor.......does you diagram show a wire going to earth.....can you post a photo of the diagram... Steve

[Philk]

Hi Steve

Yes.... here it is. The Pertronix Ignitor I have is specifically for Positive Earth Cars (model no. above).

[mgcjag]

Hi Phil....have you contacted the Distributor Dr to ask for advice......Steve

[Philk]

Hi Phil....have you contacted the Distributor Dr to ask for advice......Steve

Not yet but that could be a next step.....