Positive or negative on coil

[davecopp]

Hi
Some advice would be much appreciated.

I have a 1969 morris minor 1098 engine on a pallet in my garage which I want to do a test run on. I assume when it was in the car it would have been positive earth but as it's not I believe it doesn't matter as long as the coil is connected the right way around (there is a dynamo on it which I won't be connecting). Unfortunately the coil terminals aren't marked with SW and CB - they are marked +ve and -ve. I just want to confirm I'm correct in thinking if I connect it as positive earth the +ve on the coil goes to the distributor and the -ve on the coil is fed from the negative on the battery.

Thanks
Dave

[IslipMinor]

Dave,

If you are not connecting the dynamo, it does not matter whether you wire it up as +ve earth as you have suggested, i.e. +ve coil terminal to distributor and coil -ve to battery -ve, or the opposite as -ve earth. The starter motor turns in the same direction whether +ve or -ve earth.

Probably depends on what battery leads you have? Then wire the polarity to what you have available.

[myoldjalopy]

But once you put it back in the car and connect to the dynamo and assuming a positive earth set-up........... the current has to go to earth at the points when they close. Therefore, the +ive terminal on the coil must be the CB (contact breaker) terminal to go to the distributor via the low tension lead and thus to earth. If the car is set up as -ive earth, it will be opposite way round.

[davecopp]

Thank you Richard and myoldjalopy. Much appreciated.
Dave

[jaekl]

The way I understand it the coil will work either way but the spark is stronger if you connect it as you state. The high voltage circuit is independent of the low voltage and can be a different polarity. The issue is the direction the spark is going across the plugs.

[Blaketon]

I've never had a + earth car but the current still flows the same way; it's just that the body is live.