Classic/Antique Car Repair: Flathead Ford/Mercury V/8 1948 vintage, 12 volt batteries, ford mercury

Question
1.what exactly does positive ground mean?
2.I have no spark at the sparkplugs,do you have any idea what could be wrong?
This is a 1948 Mercury and was running OK,It backfired a couple times and stopped.

Answer
Positive ground means that the + terminal of the battery is the one which goes to chassis ground.  The "hot" side of the battery is the negative terminal - just the opposite of modern cars.

Many cars were positive ground up until the mid 50s or so, as that made the cars a little easier to start - but it caused confusion in the trade because GM and others were negative ground, so it was finally agreed to standardize on negative ground - mostly about the same time as cars started using 12 volt batteries.

None of this has anything to do with your current (no pun intended) problem.  Your symptom is the classic one of an ignition failure, so start from the assumption that you have no spark.

Step one is to run a temporary added wire from the battery negative post directly to the wire terminal on the coil that normally comes from the ignition switch.  (I'm assuming here that your car is original, and is still positive ground).   This will allow the car to start if your problem is anywhere in the switch or wiring, so if it starts now, you know the problem is somewhere upstream of the coil.

If it still won't start, your problem is a little tougher - it is possibly just a loose connection at the points or at the coil, so inspect all that carefully, and if you can't find anything wrong there, you'll need to get into the distributor and troubleshoot.  It could be points, condenser, rotor, caps, who knows!   You'll just have to be a detective, or get some help from someone on scene who knows these old Ford ignition systems.   It is very unlikely to be the coil, by the way, but that is the first suggestion you will get.  Unless you have a spare handy, I wouldn't bother trying to get a new coil until you've eliminated all other possibilities.  Coils are often accused, and seldom responsible for ignition problems - they are simple and have no moving parts to fail!

Good Luck.  

If you need more advice, please ask again - if I were right there I'd be happy to help you track it down, it is just detective work, though.

Dick.