Charging issue

Update: I re-installed the alternator for the vehicle in question after having it checked out and new bearings installed. I had taken an alternator off one of my other E-Types and was using that during the past week of diagnostics. Interestingly, the ignition light works as it should now. I stated earlier that the alternator I was using was showing 8.5 volts from the AL lead. The original alternator shows around 7.5 as suggested. I then took the "replacement" alternator to have it tested and they said it checked out fine. Could there be something starting to fail that is causing the higher AC voltage from the AL lead?

George is correct, the reading should be about 7.5V AC under normal operating conditions. But it can vary higher depending on the load and state of charge. 8.4V AC isn't necessarily a problem, but can indicate a weak alternator diode if it's persistent. It's not enough to blow the 3AW. The 3AW is pretty delicate, and can be damaged by any number of mishaps, physical or electrical.

Removing the AL lead will not cause the light to go out. Removing the WL lead should do that.

Given what you've described, it's pretty much a sure thing that the 3AW is shot. The 3AW is a thermal relay that just operates the dash indicator. if it fails, the indicator is usually on all the time. I would disconnect the leads, tape them off somewhere, and get the alternator tested. Then enjoy the car until the 3AW can be replaced. If you leave it connected, there's a small risk that the AL lead could short internally, causing alternator damage.

Joe you can drive on--you have an amp meter but the 8.4 volts is what did your 3Aw in.

AL lead shows 8.4 volts and WL checks out fine. Disconnected AL with engine running per Michael Eck and low and behold, the ignition lamp remained lit. Any thoughts on where to start with this? Should I disconnect the 3AW if I want to drive the car in the mean time?

Mike, you should add "Disconnect the AL lead and make sure the charging light goes out." A shorted wire from the light will cause the light to stay on even if the charging system and the 3AW are both fine.

Michael 9 volts will blow out the unit--The Lucas manual is very specific!

It's really pretty simple. There are three leads going into the 3AW: AL, WL and E. Disconnect the three wires, and test the three wires as follows:

1) Using a multimeter set to the AC scale, the AL wire should have about 9V AC when the engine is running. Connect one probe to the AL lead, the other to ground.

2) The WL lead comes from the dashboard lamp. We know that's fine, because the lamp is lit. But if you want to test, set your multimeter to DC and measure between the WL lead and ground. Should be something less than 12v, since you're in series with the lamp.

3) The E lead is ground, you know this is good because the lamp is lit. But just to be sure, set your multimeter to resistance and Measure between the E lead and the negative battery terminal.

If the wiring is ok, then the problem has to be the 3AW. To confirm, set your multimeter to measure resistance, and measure the resistance between the E and AL lead on the 3AW itself. Should be about 20 ohms. No conductivity means the element is broken, in which case you should throw the 3AW away before it shorts out the alternator. Measure the resistance between the E and WL, should be close to zero (your indicator is lighting, so this test is really unnecessary).

Thanks again George. The link shown on the posting by Michael Frank on August 9 gives a couple of tests for the 3AW relay. Mine did test fine based on his information but I will also try a new one. My alternator tests look ok (output, good; power to voltage regulator, good; multi-meter on battery with car running shows charging; turning lights on drops voltage temporarily and then it comes back up). If this is the case, can I assume the system is charging?

Thanks again George. The link shown on the posting by Michael Frank on August 9 gives a couple of tests for the 3AW relay. Mine did test fine based on his information but I will also try a new one. My alternator tests look ok (output, good; power to voltage regulator, good; multi-meter on battery with car running shows charging; turning lights on drops voltage temporarily and then it comes back up). If this is the case, can I assume the system is charging?

Joe I should have said Jaguar and Lucas had no direct test. Perhaps the retro engineers have devised one!

Edited on 2012-08-13 17:51:50

Joe there is no test for the 3AW direct. You test around it--you check that the lamp works (that you know) you make sure the ground is viable and then that it is getting the proper voltage from the alt. (6.5 to 7 volts I think--but look it up). If all of that is proper then the 3Aw is bad--or as Jaguar says--check by substitution! Good Luck.

I may have jumped the shark a bit. All tests would indicate that the charging system is operating correctly other than the fact that the ignition lamp on the dash does not go out. The 3AW relay tests as it should. Any suggestions?

Resolution: Once again, a huge "thank you" to this group for your assistance. The lead in to this issue was a shorted wire in the ignition harness that heated to the point of melting one of the other wires. It was after I replaced the harness that I first experienced the lack of charging and started the troubleshooting. Good alternator, battery and wiring had me scratching my head as there was no power to the "F" connection at the voltage regulator (or alternator). Finally determined that the ignition switch must have fried during the short. A new dash switch solved the problem and all seems to be in order now.

Michael a "trigger" wire is what a lot of folks refer to as F+ in this case. With what he says he has done a broken wire is possible.

What is a trigger wire?

AFAIK, all S1 and S2 E-Types have alternator relays. The purpose of the relay is to cut power to the rotor when the ignition is off. The easy way to test this is to test for voltage at the alternator end of the F+ lead when the switch is "on". Should be 12V. You can find a lot of troubleshoot help in my FAQ:

http://www.coolcatcorp.com/faqs/Lucasalternators.html

A 67 may have an alternator relay. I am not sure when that was phased in. If you have one, it is probably next to the horn relay as it is on my 68. I am assuming that the system used to work and you can rule out improper connections. Good luck

Joe check the trigger wire.