QuestionHi Howard, I have a 1972 spitfire with a Lucas alternator 16 ACR.
The Battery has 11.9 Volts but when i start the car, the battery is only reading 9 to 10 volts on my hand volt meter.I had the alternator in the shop and was told to get a new voltage regulator which i did replace. I assume the battery should read around 14 volts when car in started! Any Suggestions? Wayne...
Answer
Spitfire Alt
Hi Wayne,
The standard battery/alternator test is to check battery voltage (yours is low)(should read a little over 12v) The reading you got of 9 to 10v is a cranking voltage but a min of 9v is the lower limit a coil should see while cranking. As soon as the engine starts you should set the RPM at a fast idle (1500 RPM) and you should see 13.8 to 14.5v)
If not, you need to start testing. First confirm that the car wiring is correct. Disconnect the large and the small plain brown wires. They should be powered all the time. Disconnect the brown w/yellow tracer wire (or two) and test for power (should be no power) Turn on the ignition and note that the "IGN" light is off and then ground the brown w/yellow wire and the light should light.
Now confirm the wiring on the alt as per my attached diagram.
If everything is correct up to now you should "Full Field" the alt. Remove the plastic cover on the back of the alt. and plug the wires back into their correct positions. Connect the volt meter across the battery posts and start the engine and set it at about 1500 RPM. Take a small jumper wire and connect one end to a good ground.
(many Lucas and aftermarket regulators have different number of wires so look at what you have. Some used a metal strap from the closest brush holder to the regulator, over to the case of the regulator and others used a yellow wire from the closest brush holder to the regulator.)
It does not matter which you have, just touch the ground jumper to the contact of the brush holder that is closest to the regulator and fartherest from the rectafier. DO NOT LEAVE THE GROUND JUMPER CONNECTED LONG!!! Just enough to read the volt meter. If you see about 15v the alt is ok and the problem is either the regulator or your wiring.
Howard
