MG Car Repair/No spark on newly rebuilt MGA 1600
I've completely torn down and rebuilt my 1960 MGA 1600. In preparation to time the engine, I attempted to get a spark, but nothing... points open and close (ground/no ground). I have 12 Volts showing on the white wire going to the negative post on coil. I have the coil's positive terminal going to distributor. Connection from terminal in cap shows about 4 Ohms of resistance connecting to plug connector on other end. No spark makes its way? Bad condenser? Cap? Rotor? Bad Ground???
Do this test, first remove the distributor cap and pull the coil wire out of the cap. (if it is the screwed in wires go inside the cap and remove the set screw from the coil wire and pull the coil wire out of the cap. Then connect the coil wire to a spark plug and lay the plug on a metal part of the engine. Hand rotate the crank until the points are closed. Then turn on the ignition switch and confirm that you have 12v at the (-) side of the coil and 0 volts on the (+) side of the coil. Now use an insulated anything to open the contact points and you should see a spark at the plug. This test confirms that there is power to the coil and the points are a ground and wehn the points are opened that the coil does fire.
If you had 12v on the (-) side of the coil that shows the ignition switch is supplying power. If you have 0 volts on the (+) side of the coil, that proves that the points are closed and making contact to ground. When you open the points with something insulated and the plug fires, htat proves that the coil did transfer to the secondary winding (plug wire).
If you have all of that and have no spark at the plugs with the cap on do this. Remove the plug from the coil wire and with some kind of insulator hold the coil wire close (about 1/4 inch) from the center of the distributor rotor and have someone spin the engine over and see if you can jump a spark to the center of the rotor. If you can you have a shorted rotor.
Next take a strong light and look inside the distributor cap for any signs of "Carbon Tracking" (black carbon tracks on the center post) If so the cap is bad.
The MGA came with wire type plug and coil wires but if they have been replaced some time with carbon string wire you need to use an ohm meter on all the plug wires and the coil wire. (about 4 ohms per foot of wire is norm) Any lower reading is better.
Somewhere in all of that you should find your problem. Let me know.