|The MGA With An Attitude
How to IDENTIFY Positive or Negative Earth - ET-099
At 08:51 AM 5/5/2010 -0400, Frank Krajewski wrote:
"I stored my 1964 B and 1958 A many months ago and took the batteries out without noting the polarity. There is a way to tell by looking at the coil leads but I forgot the answer. I am reluctant to connect the battery and have it backwards. Would the fuel pump run backwards if I have the polarity reversed"?
Assuming you have not disturbed the battery connectors too much, this is an easy solution. The Positive battery post is larger than the Negative post. If you install it backward one connector will be very loose and the other will not fit on the post. In that case just turn the battery around and the connectors should fit properly.
I wouldn't rely on the coil wires having been previously correct if you are not absolutely certain. In proper form the coil "+ or "CB" terminal should be connected to battery "+", and the coil "-" or "SW" terminal should be connected to battery "-". For positive earth the distributor and engine block are "+" and the ignition supply wire is "-". For negative earth the distributor and engine block are "-" and the ignition supply wire is "+".
If you are still not sure about the original configuration, you can install it or change it to whatever you prefer. Once the battery is installed you need to polarize the generator, very simple. Connect a jumper wire to the hot battery wire and touch it momentarily to the field terminal "F" on the generator. Then connect the coil primary wires to proper terminals as noted above. For the original MGA and early MGB nothing else in the vehicle is polarity sensitive (except an accessory radio).
Some aftermarket or upgrade parts may be polarity sensitive. Check polarity requirement for a radio, electronic fuel pump or points type pump with a diode, electronic ignition module, or anything else electronic that may have been installed in the car. If the car has an alternator it almost certainly needs to be negative ground (about 99.99% certain). A very early production alternator being positive ground is extremely rare, but could happen.