Switching Polarity pitfalls?

[mrshannon]

Hi all.

I'm fitting a radio to my Minor and need to run it from a negative earth. My minor has a positive earth and according the this article is a rather simple process to turn it around.

http://www.minormania.com/html/article_ ... ative.html

Before I give it a go does anyone have any experience of this or had any problems? It seems almost too simple!!

thanks,
matt

[faversham999]

change the wires on the coil

[bmcecosse]

Haven't read the article - but just swap the battery round, and then polarise the dynamo by taking a length of cable from the non-earth battery terminal and flashing it on the small terminal on the dynamo a couple of times. Then start up and check the Ignition light is going out - and the battery is charging. Then - swap the coil wires around, clean and gap the Ignition points and clean the fuelpump points - and that's it!

[mrshannon]

ta.

When you say the 'non earth' terminal do you mean the orignal non earth terminal?...in my case the original non earth is negative on the battery ?

[bmcecosse]

No -it's the non-earth terminal AFTER you do the swap - ie in this case - the +ve terminal.......

[mrshannon]

Thanks everyone. Polarity reversed successfully. Just gotta clean and gap the Ignition points and clean the fuel pump points and I'm done!

[brother_morris]

Hi All
successfully switched my 1000 over to negative earth this afternoon.

Followed the steps in the technical tips on this site and all seems good, however...

when swapping the wires on the coil it says:

if in doubt you should end up with the black and white wire connected to the terminal marked - or neg.

The black and white wire was already on the negative terminal. I have swapped them anyhow and all seems to be working fine, but should I swap the wires back?

Any advice most welcomed.
Thanks

[bmcecosse]

Yes! Swop back - it was wrong.

[mike.perry]

When you have an old coil marked CB and SW then presumably CB is then connected from the ign. and SW is then connected from the distributor.
This assumes that all coils were made for pos earth cars. Were/are coils made for neg earth cars and how would you know?
And does it really matter?

[bmcecosse]

It matters in the internal wiring - if connected wrongly the spark is less strong. Early coils were all for +ve earth cars - hence the SW/CB marks. Later coils have +ve/-ve markings and should be so connected.

[win]

Regarding coil polarity,

To the best of my knowledge, to prove coil is connected correctly.

Remove HT lead from spark plug, try to start the engine, but no need to start it, the spark should jump from HT lead to plug.
Sometimes hard to see, put a lead pencil between them, may help.

A better way, is to connect the negative lead of a volt meter to HT lead, and positive lead of the volt meter to engine block,
set on highest range, try to start the engine, no need to start it, the needle should move up the scale, if polarity is correct.
If it does not move, or jumps down the scale, polarity is wrong.

I believe the theory is the HT spark should jump from the centre hotter electrode to the outer cooler one.


Regards Win