Positive or negative earth

[Chancer]

I have recently fired up my Elan that has been mothballed for a quarter of a century, the dynamo is not charging the battery but given the amount of corrosion on all the electrical terminals I was not surprised and put it down to a stuck bobbin or failure in the control box.

However today whilst reading the description of the plus 2 on ebay it mentioned that it still had the original positive earth which got me wondering.

I didnt pay any attention to the polarity when I removed the old dead battery, the earth lead which goes to the rear of the chassis was coloured black and the cable to the solenoid in the engine bay was blue which was inconclusive, I decided that it had probably been converted to negative earth as it has a period cassette player, an 8 track player and a graphic equaliser all fitted behind the seats, I assumed that these were negative earth as an 8 track player languishing in the boot proved to be although I didnt check the others. My memory tells me that most car hifi from the 70s and 80's was negative earth but as these are not fitted in a metal frame they could well have been wired with the positive to the casing.

In any case I am not concerned about the in car entertainment but whether I have connected the battery to the wrong polarity, the vehicle cranks and starts and the water temp guage reads correctly as does the tachometer, I havnt bothered with the rest of the electrics.

Its been 30 years or so since I repolarised a dynamo system to negative earth, I recall stroking the brushes on the dynamo to change the polarity but cant for the life of me recall what if anything was done with the starter motor and/or the instruments, I realise that the ignition system will work on the wrong polarity albeit not as efficiently.

Now for the question, given that thestarter works and the engine runs, the tacho and temp guages work can I assume that the vehicle has already been converted to negative earth or does the non charging battery indicate that have I connected the battery with the wrong polarity?

The vehicle is a 71 S4 coup? running strombergs in case there was a factory date for polaritry change.

Thanks in advance

[elanfan1]

I believe that for a 71 car you would be quite safe to assume it to be Negative Earth - I guess a quick way to tell would be to look at the Rev Counter and see what it says on the face.

[Chancer]

Thanks for the prompt reply, I will check it tomorrow.

In 71, 81, 91 or even 2001 I would have seen and been able to read the marking on the rev counter, I bet tomorrow I need a magnifying glass

[nebogipfel]

The battery clamps are different sizes assuming you have a round post battery.

And agreed it should be -ve earth in 1971.

I would suspect the control box to explain the non-charging.

[Chancer]

Flat post battery.

Unoriginal?

[Henry VIIII]

My S3 always has had flat-post battery terminals.

[Chancer]

Tacho confirms negative earth, a great tip, something in front of my nose that I would never have thought of!

[Galwaylotus]

I converted my 67 from pos to neg earth last year when I replaced the dynamo with an alternator. Best move I ever made. I changed the battery cables around, switched the coil connections, electric fuel pump connections and supplementary electric fan connections and sent my tach to Speedy Cables for conversion and calibration. The starter motor doesn't care about polarity.
It was always in the plan but when my control box (voltage regulator) failed due to corrosion, I decided to act. The alternator is a 45A Lucas. Common as mud, cheap and easy to fit. I just had to get a few bits of hardware to get the alignment spot on. I can run my fan/alternator belt quite loose so there is no significant load on the water pump pulley. The alternator puts out over 14 volts so my electrical system works better too - lights, turn indicators, etc.
There is a description and photos in the Forum from around July/August last year.

[jk952]

Sounds like you found your solution on polarity; note for interest starter isn't polarity sensitive. I found cleaning the contacts inside the control box (voltage reg) solved my charging problem when first getting my S2 going. (gen, pos gnd)

Good your blowing the dust off after so many years!
Jack

Did it come with a copy of Inna gotta de vida on 8 track?

[Chancer]

There is a Quincy Jones cartridge, some heavy metal group, probably quite famous but not my bag and one other, there are actually two 8 track players, one Sharp, the other I dont know, a Pye cassette player and a graphic equaliser.

After scouring the cooling and oil systems and refilling with fresh fluids involving running the motor up to temp 5 or 6 times I checked the compressions, initially I had 50psi on 3 cylinders and nothing on the 4th, it needed easi-start to fire up, the final compressions were a joy to behold, all 4 cylinders at 180psi hot

Oil pressure 30psi at hot idle speed.

[bob_rich]

Hi Chancer

If all the gauges work OK, especially the Tacho , then the battery is the correct way around.

I take it the charging light glows and does not go out when the engine revs if so I would look at the brushes
It the light is not on perhaps the bulb is shot.

regarding not charging could just be that the dynamo brushes are stuck in the holders and the springs are not pushing the brushes firmly on to the commutator, After such a long lay up carbon brushes could be stuck in there holders

Hopes this helps best of luck

Bob

[Chancer]

Many years ago I did experience a starter motor that turned the engine backwards, it was not a polarity problem.

Twas a HA Viva that was sold to me as scrap as it would only start with a push, never on the starter despite the guy changing the starter (which was when the problem occured) battery plugs points, distributor coil etc via numerous mechanics. I noticed that it was cranking backwards so changed the starter, a bog standard Lucas inertia starter, and the problem was resolved.

A couple of years later I came across the same phenomenon on another vehicle and finally found the explanation, suffice to say that I could have swopped the starters from one to the other and fixed both vehicles in one go.

So I am offering a prize of a virtual anorak to the person that can tell me what the second vehicle was