[Mgs] + or - Ground?

[Barney Gaylord]

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 termainals 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, electriconic 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.

Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com


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?
>....