What is the best electronic ign. My son in law has a fifty year old landrover and always has a spark problem.I suggested the above. 12v Positive earth. david

was going to say megajolt, but then there'd be all sorts of issues with positive/negative earth i think

Very simple is magnetronic module to fit in the dizzy. Reasonably cheap, reliable, easy to fit and effective.

Should be easy to change from positive to negative earth if it has no radio etc. change low tension leads over on the coil , disconnect the small terminal from the dynamo and use a small jump lead from the battery positive momentarily touch to small terminal to reverse polarity. Fuel and temperature gauges should be unaffected. Should then be straightforward to convert ignition to electronic.

You might be able to use luminition as well, they are pretty good optical based systems. Megajolt is the 'daddy' but i found that the luminition kit was pretty spot on.

I vaguely recall it having an earth wire (As opposed to grounding the case.) , so I'm sure you can wire it up correctly in your case.

How difficult is it to reverse the polarity of a pre transistor age car?