What do you want for Christmas..A new polarity? or Changing your Rover's electrical polarity
Original Author: Alan J. Richer
So, after all this time you want to put in a radio better than the old VW radio bolted to the bulkhead - or you're simply tired of the 1970-vintage CB you have that's the only thing you could find that was positive ground.
Cheer up - polarity conversion is a task that should take you no more than an hour even if you're leisurely about it.
In order, the tasks we're going to perform are:
1). Check the car's present polarity
2). Disconnect the battery and disconnect any polarity-sensitive items
3). Disconnect and reverse the ignition coil
4). Reverse wiring to gauges
5). Reconnect battery
6). Re polarize generator
1). Check the car's polarity:
With a Landy, it's often hard to tell what the polarity of the car is, as you can't exclusively rely on the manufacture date. Some kind soul may have reversed it already - you need to just check to make sure the positive terminal is indeed connected to the engine block or chassis ground.
With this, survey the vehicle for add-on electrical items such as tachometers, radios and the like that will be polarity sensitive. These need to either be disconnected and removed or (if equipped) have their polarity switches flipped to negative ground once the battery is disconnected.
If you have an alternator rather than a generator then either the car is already negative ground, or if actually positive ground then you can't convert it without replacing the alternator and its ancillary wiring. Alternators are polarity sensitive and can't be re polarized like a generator.
2). Disconnect the battery and disconnect any polarity-sensitive items:
It's safer to disconnect it and have it out of the vehicle before you do anything else - this way the possibility of embarrassing short circuits is removed. While disconnecting the battery examine and replace as needed the battery terminal clamps - some of these can't be swapped around because of terminal size. Two new cable clamps will only be a few dollars, and is a good investment in solid charging and starting in any case.
After the battery's out, flip the polarity switches or disconnect and remove an polarity sensitive items. You wanted a new radio anyway...now's the time!
3). Disconnect, reverse and reconnect the ignition coil
This is simple though it sounds a bit daunting. Ignition coils are polarity sensitive, and the car may start and run without swapping it but it will run a lot better if you do.
Loosen the coil clamp and rotate the COIL 180 degrees.
4). Reverse wiring to gauges:
The ammeter and fuel gauges on early Rovers are polarity sensitive, not in their operation but in the direction they will deflect. Because of this, we need to get in behind the panel and swap the wires on the ammeter and the fuel gauges so they read in the right direction.
This is basically self-explanatory - dismount the panel, find the gauges in question and swap the two wires on the back of each with its compatriot on the other end of the gauge.
5). Reconnect battery:
With the major electrical wiring items complete, now the battery can go back in. Reinsert the battery in the holder with its position reversed, and reconnect the battery cables with the negative side to the engine block or chassis ground wire.
Don't start the car just yet - we have one more electrical task to perform before we are ready for a road-test - we need to re polarize the generator. This is a very spooky term for a simple task, simply involving a length of wire.
6). Re polarize generator:
Spooking sounding but very simple process - we need to change the magnetic polarity of the coils in the generator to suit charging the battery in a negative-ground car.
Disconnect the two wires connecting to the field and output lugs on the back of the generator, noting which goes where (though they are hard to confuse as they are different sizes).
Take a length of wire sufficient to reach the back of the generator and hook one end to the +12 terminal of the battery. Tap the terminals on the back of the generator a time or two with the free end of this wire - you should see a spark when you do so. Reconnect the wiring to the back of the generator and this is done.
With all of this done you're ready to go for a test drive. Put in the key and with the bonnet open turn on the ignition - all of the panel lights should light as usual, the fuel gauge rise as it did before and with the headlights turned on the ammeter should dip as it did before.
Start the car and rev the engine briefly. The generator warning light should go out and the ammeter should show a charge going into the battery.
Try all of the ancillaries - heater, wipers, lights and the like to ensure that you didn't inadvertently knock something loose in the process of doing other things. If all is well then pat yourself on the back - you now have a negative-ground Rover!