Electrical issue - any ideas?

[Mathernet]

Ok , looking for some guidance as i fear i may be jumping down rabbit holes.

1969 2 1/4 petrol SWB. The car has been running but has very little use since a gentle preservation 4 years ago. Recently the car developed a mis fire when cold which seemed to fade when warm. This progress suddenly last week to won't start with very occasional weak firing whilst cranking.

In my attempts at diagnosis I suspected the coil as I was unable to get a spark from a plug. The coil was changed for new Lucas unit and a very weak spark was occasionally mustered by grounding the coil negative. Plugs have been changed with new as they looked a little black. The engine earth has been removed, cleaned and replaced and I have a good negative connection to the battery

Now for the weird bit - with the ignition on I seem to have 13v at the coil pos but zero ohms to the battery negative. This doesn't make any sense unless I am missing something. When the ignition is off there is no draw on the battery, with it on and the coil disconnected I am getting about 0.5 amps

could this be the cause of the week spark or is there a reason for this and i am wasting my time?

Thanks for reading

[pop058]

Restance measurement ( ohms) is usually done with no external power applied (key on) as this could affect the meter reading.
Have you tried hot wiring the ignition, checked points and condenser.

[Blknight.aus]

Points and condensor.

[JDNSW]

Check these :-

1. check voltage at switch side of coil - should be pretty close to battery voltage with the ignition on and the points closed (take the distributor cap off to see this, turn engine until closed. If it isn't, you have a bad connection, possibly a faulty ignition switch.

2. Check voltage on distributor side of coil with points closed. Should be very close to zero. If it is above say 0.5V, points probably need replacing or the wire inside the distributor earthing the contact plate is broken.

3. Check it is battery voltage at the same point with the points open. Check gap.

4. Check condition of all high tension leads - unplug and look at both ends. If any look burnt replace the lot.

5. With points closed and ignition on, opening the points with a screwdriver should give a good spark with the HT lead from the coil held 5mm from the engine. If the spark is weak and 'thin', replace the capacitor.

6. Another fairly unlikely possibility is a poor earth connection between the body (assuming the coil is on the firewall) and the engine - check for any voltage between the two with ignition on and points closed.

The current draw with the coil disconnected and ignition on is probably the fuel gauge(and temp if later setup) and possibly any extra accessories such as radio etc.

[1950landy]

I would be looking at the points & condensor also. The condensor is a small item but can cause a lot problem , also chech the earth in the dizzy.

[Mathernet]

Thanks all - i will work through these and report back