Ele. Tech Tip # 2


Charging system problems? This tip will cover most charging systems on most British cars with an Alternator. The repair of a charging system will usually bring you down to three basic areas;                        

  1.   The Alternator itself at fault
  2.   The Regulator (internal on most alternators)
  3.   The Electrical system of the car itself. (Wiring, battery, switch etc.)

It is not very difficult to isolate the fault to one these three areas. The minimum tools necessary to do the job are a voltmeter. An amp meter would be nice to have, keeping in mind that "Voltage" is the amount of "PUSH" and "AMPERAGE" is how much is actually moving. I'll also show you a short cut test that can be done with just a test light. (Standard bulb type, not an LED type). If you have added any electronic equipment to your car you should disconnect them before doing any of the following tests.

We will do the "Test Light" shortcut first as it only applies to a British car with an internal regulator in a Lucas alternator. What! You say; how do I tell if I have an internal regulator?     Look on the back of the alternator. If you have one or two large brown wires and one or two small wires plugged into the back of the alternator, then you most likely have an internal reg.       First step is turning the ignition key to ON, not start. Is the light on that is labeled "IGN" on? (I never have heard why they labeled it "IGN" when it has nothing to do with the "Ignition System") Three possibilities now with the switch on.   

  1. Light is ON
  2. Light is NOT ON
  3. Light is ON DIM

Go to the back of the alternator and unplug the wires. Did the "IGN" light go OUT?  If the light was "ON" and unplugging the wire (exciter)  made the "IGN" light go out, and then you have completed the test of the "exciter" circuit. Read the rest of the tests FYI until we get back to yours.

If the IGN light was ON DIM and it went out, you are not done. If you only had one small wire system. Connect the alligator clip of your test light to the hot big brown wire. (The large brown wire/wires must be connected to the alternator, if it's a large formed plug and you don't know how to remove the small wires from the plug, e-mail me and I'll tell you how to do that without harming the plug) Touch the probe of your test light to a ground to confirm the test light circuit. Then touch the probe to the pin on the back of the alternator that the "exciter" wire was connected to. The test light should light brightly. This is the same test if you had "NO IGN" light on with the key "ON".  Attach the test light so as to keep the test light ON. Sometimes you can attach the alligator clip to the exciter pin on the alternator and probe the hot large brown wire. What you are doing is substituting your test light as the exciter circuit. Start the car and your test light should go out. On a two small wire system, one is the exciter wire as we have been testing and the other is a "HOT" all the time or a "HOT" with the key ON. This is usually used as a voltage sensor wire for the regulator. So, confirm that it is either hot all the time or hot with the key in the ON position. If your "IGN" light was not ON but the test light "test" worked correctly, first check the "IGN" bulb. Then check the power to the bulb and the wiring.  

If you have completed these tests and you still have the IGN light and the test light ON when the engine is running above idle  then you know the problem is either the reg. or alt. (Provided you know that you have a good battery) WHAT!   You say if it is an internal reg. you don't know enough about it to go into an alt. and change a reg? Come on, don't be a wimp. It's not hard.

Unplug the wires. Take the plastic cover off of the back of the alt. Plug the wires back in with the cover OFF. You will see three major things on the back of the alt. A stack of square plates. That's the rectifier. In the middle is a plastic tower that houses the two brushes inside. Then mounted at an angle on the plastic tower is a small box with some wires coming out of it. That is the Regulator. In this case Lucas must have hired some of the FIAT electrical people. They couldn't seem to make up their minds on how many wires they needed to use. We will get to that later. First look for a GREEN wire coming from the reg and connecting to the top of the plastic tower (brush holder) If there is not a green wire then their will be a thin sheet metal strap from the top of the reg case extending over to the top of the brush holder or "brush box" (plastic tower). This STRAP or GREEN wire is the point of our next test. This test will determine if the fault is in the reg. or alt. It's called "Full Fielding". The tools needed for the test are; A wire connected to a good ground and someone to start the engine and watch the "IGN" light. What! That's all I need? YES!  

First you hold the end of the grounded wire and have your assistant turn the key ON and confirm "IGN" light ON. Then start the engine and set the RPM at just above idle and confirm the "IGN" light is still ON. Now, you touch the grounded wire to the reg. metal strap or end of the green wire at the top of the brush holder. AT that point did the "IGN" light go OUT?

If it did. The reg. is bad and the alt. is probably OK. If the "IGN" light is still on then the alt. is bad and it doesn't matter if the reg is good or bad as you can't test a reg. with a bad alt. and if you have to buy an alt. it always comes with a reg.

One last easy thing to look at before you rush out to buy that alt. is the brushes. Remove the alternator. In the top of the brush box/brush holder are two small plates each held down with a screw. Remove the screw and lift the little plate up. You will find a spring and a little carbon brush under each. The brush even though it's black carbon, it should still look smooth and polished on the end. With a light look in the square hole it came out of. The bottom of the hole should look copper or brass colored. Rotate the pulley as you look. If you find a bad brush, you may want to first try a new set of brushes, as they are not expensive. If you had found a bad reg. before you buy one compare the price of a new reg. vs. a rebuilt alt. as some applications have the new reg. as expensive as a rebuilt alt.

If you are going to change the reg. first draw a little diagram of where each color wire goes from the reg. It is not uncommon for the replacement reg. to have fewer wires than the original. If it has more wires, be sure an instruction sheet comes with it before you leave the store. If you run into trouble in this e-mail me and I'll try to help. This is the area I believe Fiat got into Lucas.

Now, if you have a voltmeter. Do the same tests with the test light and the voltmeter connected across the two posts of the battery. A normal charge at above idle is about 13.8V to 14.5V.  A "Full Field" test should be about 15 or 16 volts at 1500 RPM.  


The test to see if the fault is generator or regulator is also a "Full Field" test and is done with a voltmeter across the battery/s The voltmeter can be connected at the hot post on the remote starter solenoid for easy access. On the Lucas generator system you only have two posts on the back of the generator. The larger post is the "D" (I think it stands for dynamo) and the smaller is the "F" or field. The connections are similar to the connection for "Polarizing" as we covered in an earlier tip. Only this time the test is conducted running at about 1500 RPM. Connect a heavy gauge wire (12 gauge) to a large flat spade or Eyelet connector. (Which ever is correct for the connection on the back of your generator. Add a pigtail (can be 14 gauge) to the heavy connector and add a small connector to the end of the pigtail that will connect to your small post on your generator. Now you have a heavy wire that is connected to both posts on the back of your generator. Have someone start the engine and hold the RPM up to about 1500. Now you touch the end of the heavy wire to the hot post of the starter solenoid and read the voltmeter. You should see 15 to 16 volts. Don't leave it connected for more than a few seconds.  If you see 15 to 16 volts and you had a "IGN" light on when running. You have a bad regulator and/or wiring, because the generator is OK. If you only show battery voltage then you have a bad generator. You can not test a regulator with a bad generator so it would be wise to replace the regulator also if you have to replace the generator.

Full Field Alternators and Generators