POLARITY AND THE PETROL GAUGE

One of my reasons for having the car delivered rather than driving it home was the lack of working Petrol and Temperature gauges. The Lanchester had a gauge which was split to show both petrol and temperature readings and these were generated mechanically using very narrow piping from Radiator and Petrol Tank to the back of the gauge. Unfortunately the piping from the Radiator was not there any more, and as the 'Petrol' part of the gauge was completely clogged up where liquid should have been able to move in a calibrated glass tube I decided to go electric.

Tracking down appropriate kits was not too difficult and fitting was O.K. although I did have to drill new holes in the Petrol Tank Sender to fit the existing screw holes in the Tank.

Wiring up the various connections behind the dashboard was a fiddly job but eventually I got there. I re-attached the battery terminals, switched on, - and nothing happened. The reason - my car was wired for Positive Earth although my handbook had a diagram showing Negative Earth. I said to myself  'Part of life's rich pattern' or something similar, and returned to my supplier who advised that they did not have a Petrol Gauge specifically dedicated for Positive earth wiring but assured me that all I had to do was swap over the connections to the gauge - WRONG!

Insruments

Switching the wires around did not work, whatever the permutations tried, and the retailer then said that since the gauge was not adjustable, if I wanted a petrol gauge that worked the answer was to change the car polarity to Negative Earth. They assured me that this would be simple with a pre-war car with few devices likely to be sensitive to polarity/non-adjustable (like the petrol gauge they sold me) and this time thankfully they were right.

engine - nearside

One thing I omitted to do before starting was look at the direction of rotation of the two independently operated  window mounted wiper motors so that the connections could be switched if rotation was reversed. With a permanent magnet motor this apparently could be harmful, but my motors still work and as the car wouldn't normally be outside at present if it were raining (window seals /trim need a little attention to make them fully waterproof), temporarily switching polarity to check this point is low priority.


STEPS TAKEN TO SWITCH POLARITY

1. Battery leads disconnected and battery turned round (in battery compartment - B above). Left the battery disconnected, but with lead terminals swapped as the battery posts differ in size.
2. Low tension Coil connections SW and CB switched. The coil (A) will still work but at reduced efficiency if the wires are not correctly connected.
3. Switched the wires at the ammeter terminals.
4. Connected battery Positive terminal, and to test for any untoward flashes, bangs or sizzles from the electrical components touched the other battery lead to the battery Negative terminal - there weren't, so tightened up the terminals.
5. Dynamo polarity must be altered and I did this by disconnecting both wires from the dynamo and then with a length of wire attached to the battery Positive terminal I touched the other end to the dynamo field terminal (which generated a small flash) for about two seconds - and that's it.

There is an alternative method which involves disconnecting the leads to the F and D terminals on the Voltage Regulator and making sure that the D wire doesn't touch anything. The F wire, or an extension from it is stroked across the battery feed terminal on the Regulator, (A on my two bobbin Voltage Regulator, but B on a three bobbin Current Regulator) three or four times creating a spark each time. Then reconnect the wires in their original positions and that's it again. 

Wiring

All reasonably straightforward because I didn't have electronic components, (other than the petrol gauge!) radio, tape/disc player, electric fuel pump, heater or other exotic add-ons which would have needed further investigation and might turn out to be polarity sensitive/non-adjustable.

(The clock would also have required looking at - and I looked at mine and discovered it was clockwork and hadn't been working only because I hadn't wound it up).

Finally I switched on the engine and everything worked - including the Temperature and Fuel gauges -  which I must say gave me a great sense of achievement.

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