Converting my Plus 2 from Positive Ground to Negative Ground

[RedFive65]

Greetings!

I love my +2, but I can't run the headlights and windshield wipers at the same time. I also can't use my GPS or charge my phone. The Positive ground/generator system must go. I ordered the 45 amp alternator from R D Enterprises and he told me to have my tachometer converted to a solid state one so it would continue to operate. My ignition is electronic, so that has been taken care of. I'm sending the tach off to be converted so it will not be an issue.

My mechanic is a wizard but I would like to have a step by step procedure to help assist him in the process of converting the +2 from Positive to Negative ground. I saw the "Wheeler Dealers" episode where Ant converted a Triumph from "+" to"-" and he made it look very easy. It was on television, so it had to be true! LOL!

Has anyone here upgraded their car from Positive to Negative and has some advice to share?

Anything tips will be greatly appreciated.

Thanks!

[ericbushby]

It is not difficult to change the polarity of the existing tachometer. There are only two connections to change over on the circuit board. While you are there any electrolytic capacitors should also be replaced.
I did mine easily but I am quite handy with a soldering iron.
It has been written up on this forum a few times already and you might find it using the search system (top right).
Otherwise the specialist instrument repairers will do it and probably fit a modern system inside.
Eric in Burnley
1967 S3SE DHC

[RedFive65]

Thanks for the advice on the tach.

My main concern is the entire process of converting from positive ground to negative. It looks simple, but I know that a errant wire or connection can fry a wire loom very quickly!

Thanks!

[benymazz]

I converted my S2 from positive to negative for the same reason - I upgraded to an alternator.

I believe the only things that I did were resolder the tach for correct polarity (as has been stated previously) and swap terminals on the ignition coil around. I'm not sure what gauges the +2s have but if you have a voltmeter or ammeter I suspect those will need to be reversed.

My father had previously converted the car to an electric fuel pump which was wired for positive ground so I had to reverse that as well.

Check rotation of the blower motor and wiper motor. Moss Motors has an article describing what to look for if you type "moss motors converting to negative ground" into google.

Another reason I converted to negative ground - it allowed me to run LED taillights and turn signal lights that are brighter than incandescent bulbs. Other drivers are notoriously lousy, so being visible is a top priority for me.

-Ben

[RedFive65]

Ben;

Thanks for the information!

My tach wasn't very accurate anyway, so getting it modified will kill two birds with one stone.

I think my Amp gauge is wired wrong as it reads "negative" when it s/b charging, so that one I'll probably leave alone.

I saw the Moss Motors article on-line, so I'll have my mechanic look it over when he works on the car.

I'm hoping to drive it to LOG event up in West Virginia this fall, if I can get everything working like it should. Changing the electrical system should go a long way in making that a reality.

[benymazz]

See you there hopefully - I’ll be making the drive down from NY in my S2.

-Ben

[joe7]

Regarding the amp gauge, if (big if here as I did mine 40 years ago) I remember correctly just switch the wires.

[stugilmour]

When looking over the ammeter, note that the gauge face has the positive position on the left side of the face. Perhaps this is a vestige of the original positive ground; ie the system is charging when the needle is in the ‘upper’ or right side of the gauge face.

At least that is how the stock ammeter was on my ‘69 Federal Plus 2, which was born as a negative ground car. This actually caused us a problem when we first bought the car. We visually saw the needle in the ‘upper’ side of the gauge face and thought we were charging fine. Turned into a rather long day when we ran the battery down. Live an learn. Gosh, was that really fourteen years ago….

viewtopic.php?f=45&t=16492

I think I mentioned this in an earlier thread on this topic, but if you are going to be using an alternator one should consider ditching the ammeter altogether and replacing with a voltmeter. Lotus recommended this change in the Plus 2 Work Shop Manual. The voltmeter wiring is way lighter than the ammeter, and allows the main unfused charging cable to be moved to the firewall, which seems somewhat safer to me.

When I rewired my car I purchased a vintage Smiths Voltmeter (often called a battery condition gauge) on eBay as per the WSM pictures. It really didn’t work very well, and the gauge face is a poor match to the other minor gauges. I have since replaced it with the new Smiths currently available voltmeter that actually matches the stock gauges better and works much more reliably.

Here is a picture of the currently (no pun intended) available Smiths Voltmeter for reference. The lettering is very close to the other gauges. You may have to change the gauge light socket to fit. This is an awkward job with the dash fastened into the car, so perhaps make a list of any other items that may require dash removal.

[RedFive65]

Thanks to everyone that gave me some needed advice on this topic!

I'm sure that it will work out fine, but it never hurts to get all the information you can.

See you out there!

Thomas Reimer

To the people in the UK, we will be touring there later this month. We can't wait to see everything the UK has to offer and of course, we are going to see Classic Team Lotus and the Jim Clark Museum. It should be fun, once I get used to driving on the left side of the road!