Mysterious Drain

OK weather is starting to get nice and so I am back trying to track down this gremlin. I took a measurement as Michael Frank advised and I come up with 2 volts between the "L" terminal and ground, and 12 volts between the "S" terminal and ground. Both readings are with the key in the "on" position

Any help would be greatly appreciated

OK weather is starting to get nice and so I am back trying to track down this gremlin. I took a measurement as Michael Frank advised and I come up with 2 volts between the "L" terminal and ground, and 12 volts between the "S" terminal and ground. Both readings are with the key in the "on" position

Any help would be greatly appreciated

OK, I will start there and report back, thanks for the help

Now we're getting somewhere. If you examine the wiring more closely, you should see that the two wires DON'T connect to the 4TR. The S is a sense lead, probably not needed. if it's connected at all, it should be connected to the alternator relay behind the left mudguard, in front of the battery. But the L must connect to the ground lead (WL) coming from your dash lamp. If you follow this lead, it's probably interconnected to the WL lead on your 3AW, which is the cylindrical relay bolted to the firewall.

Simple test: attach one lead of a voltmeter to the lead that goes into the "L" terminal, the other test lead to ground. Then turn the key to the on position, but don't start the motor. Your meter should register a little under 12V. If not, the problem is in the lamp circuit. Is the light coming on?

Do a similar test with the lead going into the S terminal. It should have 12V, but ONLY when the key is in the on position.

The alternator has a heavy guage grey wire coming off it stamped "B" on the alternator, this goes to a fuse block on the heat shield which the brake and clutch fluid bottles are on. The other wires coming off the alternator are on a molded plastic connector, it is marked "L" and "S" on the alternator, these two wires go to a box near the battery marked Lucas 4TR Alternator Control

I would start with the most obvious...try a known good battery.

Is the alternator a Mitsubishi or Nippondenso? If you have a modern alternator, the voltage regulator on the bulkhead probably does nothing. Modern alternators usually have an internal regulator.

There must be a connection between the alternator's internal regulator and the instrument panel light. If this is disconnected, the alternator will never charge. Same will happen if the dash light is blown. You should take a few minutes and try to trace out the wiring diagram, otherwise I can ony guess how it's set up.

George, are you speaking of the box to the right of the battery marked "Lucas alternator control"?

George, are you speaking of the box to the right of the battery marked "Lucas alternator control"?

George, are you speaking of the box to the right of the battery marked "Lucas alternator control"?

George, are you speaking of the box to the right of the battery marked "Lucas alternator control"?

don't know if this helps but here is a picture of the alternator

Something must have gotten wet when it overheated, the car never gave me a problem before that. the alternator is one of the only things not original to the car, its a mitsubishi that worked fine before.

I encountered a similar battery drain problem on my '65 E-Type. It turned out to be that the starter solenoid was not completely retracting and was continuing to draw current following the start cycle. A few smacks (of the solenoid) with a wooden mallet and more regular use solved my problem.

Good luck,
Dick

I assume that by 1969 Jag's would have moved on from generators to alternators. If so, a common discharge path is often one or more shorted diodes in the alternator.

Lacking an ammeter to measure reverse current flow through the alternator with the engine stopped, you could try disconnecting the output lead from the alternator to eliminate that as the possble discharge path.

Do not disconnect this lead with the engine running.

Just a couple of comments from my limited knowledge about these things.

With the car at rest and ignition off there should nothing drawing amperage at all from the battery. If a spark occurs when you connect a terminal to the battery, then yes, something is drawing current that shouldn't be. Be certain that no small lights are on, or the radio. I just can't think of anything that should be energized with the ignition off. See if anything "works" that shouldn't be working with ignition off. I'd probably fault the ignition switch itself. Give it a blast of WD40 to loosen up the tumblers.

If there is no spark at the battery terminal, then I would suspect the charging system. With the car running, and testing with a volt meter, there should be about 13.5 volts on the battery. If not, then your alternator is not charging the battery. If you do have 13.5 volts on the battery while running, then I would suspect a bad battery. If you drive it regularly...and it sounds like you do...go the extra expense of getting an Optima battery.

On the overheating, I always use a 50/50 mixture of coolant to water, and I add a bottle of Purple Ice or Wetter Water. I found my cap was not holding pressure and was spitting out fluid through the overflow tube. I replaced the cap with a 10 pounder and haven't had any problems since.

Good luck.

P

I do not know why overheating should affect this but I suspect the voltage regulator--did it get wet from the overflow of your header bottle?