MG Car Repair: 1973 MGmgb 4cyl, voltage drop test, starter solenoid

Question
car. . has new coil 12volt,new distibutor new points&condenser.new spark plugs&wire,s starter has new brushes.car has spark.but some thing is drawing the battery down fast as i turn it over.

Answer
Hi Richard,

First charge the battery and then check the battery voltage. It should read 12v +. Leave the volt meter on the battery and try to start the car and watch the voltage. As it spins the starter it should not drop below 9v and should stay above 10v. If it drops below 9 to 10 v and slows down spinning the engine very quickly you need to first check the ground strap between the engine and the frame and the positive and negative cables by doing a voltage drop test (under load)

The method of doing a voltage drop test is to put the positive prob of the volt meter on the engine block and the negative test lead on the negative post of the battery (not the cable end). and try the starter. While the starter is engaged the voltage should not reach .5v. This shows how much voltage is lost just in the ground circuit. Do the same on the positive side by putting the positive test probe on the positive post of the battery and the negative test probe on the starter solenoid that the battery cable is attached to and try to start the engine. This tests the positive cable.

If they are ok and you have charged your battery and it slows down quickly when spinning the starter you need to have the battery "Load tested" most any auto parts stores will run the test free.

It is possible too that a "Dragging" starter can run a battery down quickly and an amp draw test on the starter motor should be done too (again most auto prats stores have the equipment to do that and usually do it free of charge.

Be sure to run the cable "Drop tests" first.

Howard