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Date: Tue, 14 Apr 1998 06:35:04 -0600
From: "Janssen, Lee K"
Subject: Alt Warning Light (was DAN MASTERS IS BACK!!!!)
Dan Masters writes:
There are two ways for the voltage to be low:
> 1) the wire from the bulb to the alternator could have a
"partial" ground -- not enough to make smoke,
> but enough to keep the bulb lit.........
I had a similar problem last year.
FIRST look at the fitting that holds the alternator warning bulb in the dash. After 25 years the plastic has a tendency to crack allowing the bulb holder to ground out. The outside surface of the bulb connector goes to the alternator effectively grounding the field windings. As a result you get no voltage from the alternator and no smoke. On the other side of the circuit the bulb is connected to positive voltage, the net result is the bulb is always lit and since we have a resistive load (the bulb) again no smoke. If you remove the bulb holder from the dash and the light goes out you immediately know where the problem is.
Hope this helps
Lee
OR
Date: Fri, 10 Jul 1998 19:52:09 -0400
From: Dave Massey
Subject: Re: TR6 Charging Problem
St. Lupus writes:
Okay, I think I've calmed down enough to ask for help on this problem without using any swear words. Basically the problem is this: Last Friday, I replaced my points ignition on my 74 TR6 with a Crane electronic ignition. It seemed to run beautifully, no hesitation and didn't miss once. However that night, while driving home I noticed that all the lights seemed pretty dim and that the volt meter was rapidly dropping. The solution was obvious, drive w/o the lights and pray I made it home. With the aid of a little luck and a sympathetic policeman, I was able to coast the last few feet into my parking spot.Basically when running the car I am not getting any charge into the battery at all. The voltage across the battery drops when the car is running. I've spent the last week trying to figure out what the problem is and can't figure the damn (oops there I go) thing out. The obvious culprit was the alternator (lucas 2 wire regulator), but having it rebuilt (twice) didn't help at all. The Ign light comes on when the key is in the on position, but goes off as soon as the car is started.
Please help!
Thanks
Dave Massey replies:
Check your big brown wire. It runs from the alternator output to the multi-tap on your red battery cable. If this wire is not making good contact than your Alternator may be working just fine but the current is not making it to the rest of the electrical system. And I've seen this before.
If you have a voltmeter, unplug the brown wire from the alternator and measure the voltage at the tab. Compare it to the battery voltage with the wire hooked up. Is it the same?
The problem may be (fingers crossed) that the multi-tap (or whatever it is called) gets corroded (being close to the battery) and current doesn't flow.
If this doesn't fix it you just might have to spend some money. ;-(
Dave
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Date: Fri, 10 Jul 1998 22:49:27 EDT
From: Dan Masters
Subject: Re: TR6 Charging Problem
OK, this is going to call for a little detective work! Assuming your alternator is good, (and you have tested it to confirm that, per your latest post), then the problem most likely is in the wiring somewhere, or you have a very bad battery (both items mentioned by Dave Massey and Malcolm Walker - and good advice, btw).
The first thing you need to do is check out the VTR article on how an alternator works, which will help you as you trouble shoot the problem. The URL is:
http://www.vtr.org/maintain/alternator-overview.html
If it is the battery, then it will drag the alternator voltage down with it. Since the warning light sees battery voltage on one side, and alternator voltage on the other, it will not light under these conditions. I doubt that this is the problem, though, as that would put an extreme load on the alternator, and you would probably get smoke! Not an impossibility, but unlikey. That battery can be checked at the same place where you had the alternator checked. And, if it were the battery, you would notice it when you tried to start the car, as the cranking would be slow at best.
If it is not the battery, then it must be the wiring. An alternator needs three connections to work: The warning light connection, the system voltage monitoring connection, and the output connection.
Since the red light comes on when you turn on the key, and goes out when the engine is running, it is safe to say that this connection is OK (and a good indication that the alternator is working).
You said you have an alternator with a "Lucas 2 wire regulator." This may be where your problem lies. TR6s came with a three wire input plug in '74. If you are missing one of the connections, that would account for the low voltage in the car.
Take a look at the back of the alternator. You should have three wires - one small brown/yellow, one small Brown, and one large Brown. The small Brown/yellow is the warning lamp wire, the small Brown is the voltage monitoring input, and the large brown wire is the output.
Check for voltage on the small brown wire. There should be 12 volts on this wire at all times, key on or off (test it with the key off). If you don't have 12 volts, trace the wires to find out where the break is. Most likely, it will be at the main battery cable connector, as pointed out by Dave.
If you do have 12 volts, look for a break in the large Brown wire, probably at the same connector as above.
You should, as a matter of course, check, and clean if needed, the battery cable to the starter solenoid. I don't think this is your problem, if you are having no trouble cranking over the engine.
It is possible that you have a two wire alternator, but if so, it came from another car, not a TR6. Some MGs, for example used a two wire. In this case, the small Brwon wire is internal to the alternator, and measures system voltage at the connection to the output terminal, the large brown wire. If that is the case, then just check for bad connections in the large Brown wire. That is just about all I can think of. Let me know if that helped. If not, I'll try to think of something else.
Dan Masters,
Alcoa, TN
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The TR6 Procedures Page - Maintained by J.B. Zimmerman - Content by the SOL!
