MG Car Repair: starter/solonoid-79 midget, voltage drop test, starter motor

Question
Hello howard, Got the power back to the ignition system.  Now occationally when I turn the key, on single loud click, and not starter movement.  do you think starter or solonoid?  
As always, thank you!
john

Answer
Hi John,
The "click" is most likely the click of the solenoid. But that don't mean that the electrical connection inside was made to the starter motor. So you need to run some tests when it is in it's failed mode. (click, but not spinning the engine).
There are several tests that need to be done. First you need to know if the solenoid made the electrical connection to the starter motor. To do this you need a test light connected to the starter motor when it failed to spin. If power was applied to the starter motor and nothing spun, then it is either a bad starter motor or a bad bendix on the starter. Another test is to put volt meter leads on the engine block and the negative post of the battery. (+) lead to the engine block and (-) lead to the negative post of the battery when you get a click that does spin the engine. This is a "Voltage Drop Test" of the ground circuit. (you should see less than .5v)
Another test is to put the (-) test lead on the power cable on the starter motor and the (+) test lead on the (+) post of the battery when you spin the engine over.
An old mechanic's quick test of battery cable connections is to hold the key in the "Start" position when it fails for 20 to 30 seconds and quickly feel the battery posts for heat. If a poor cable connection happens when you get a "Click" but no starter turning, heat is produced at the poor connection where ever it is.
Howard