In that i'm not nearly as smart as I once thought, and that I have never really figured out car charging systems, I appeal for advice before I go digging into this one.

Half way to the in-law's last evening the alternator light came on. Peculiarly, the instruments (fuel, oil temp, water temp, tach) also began reading extremely low...e.g. fuel gauge went from full to almost empty.
No turn signals either.

So I dropped off my wife and immediately went home, hoping to beat darkness and the need for lights assuming I was running a total loss system. Guess I went about 18 miles with the alternator light on. And i made it. When I got home, engine still running, I measured the voltage at the battery teerminal. About 13.85.

I assume my old Bosch 35 amp (or it is 35Watt?) alternator finally outlived itself. But that instrument light thing has me puzzled. I know these things have voltage stabilizers for the instruments. Could it be there's a reference voltage directly from the alternator? How can I test the alternator? Voltage regulator?
If it's a bad alternator and I replace it with a Bosch 55 amp unit with an internal regulator, what re-wiring is required?

Hope someone out there can help me out with this. And i hope the solution is as simple as a new alternator.

Most likely the fuse that feeds the dash has a poor connection.

Alternator light glows when the alternator is putting out either more or less than what it senses the battery has. It glows when it's not charging because current is flowing in one direction, it glows when it's overcharging because current is flowing in the opposite direction.

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Three 164's, Two 144's, One 142 & a partridge in a pear tree.

Sounds to me like you have lost your ground connection .... perhaps at the dash... but try cleaning your battery terminals and any ground points you can find .... If that doesn't clear up the problem then look at your voltage regulator and alternator ..... this being an 1800 and having an alternator suggests that someone has been into the electrics before you and installed the alternator in place of the generator. When Ole Reliable still had the generator, I was treated to a flickering charge light that I was informed was an "optional at no extra cost entertainment device" and was just one of the idiosyncrasies of the 120 models....

Good luck

Brett

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Brett Sutherland & the 1.6 million mile 122 CANADIAN --- and has been Joined by a 1990 780 BERTONE TURBO Coupe -- WINDSOR, Nova Scotia the birthplace of HOCKEY

Thanks, Brett. In my paniced haste I forgot to note this is a 70 E. So the alternator was factory. Just had a ne battery installed a few weeks ago so I think the posts are OK. But I'll check those grounds.

You said 13.85 volts.
With the engine running?
Sounds like it is charging fairly well and your light shouldn't have come on.
Cleaning connections (don't forget the fuse box and fuses!) may help.

I really am dumber than I look. Brett's and your replies allowed me to think straight instead of having alternator on the brain.

First I eliminated the alternator and regulator as problems by making three simple tests with a voltmeter Won't go into detail here as there are numerous web tutorials.

Next I visually checked the fuses. Seemed OK. Then I put the driver's seat back, got my flashlight and started looking up into the dog's breakfast of wiring that lies behind the dash. Not that I've memorized it, but I didn't see anything that seemed problematic. But something called me back to the fuses. Perhaps it was the pain caused by that horrible seat adjustment knob which sticks right into your back when you try to do under-dash work. Next time that seat is out I'm going to see if I can switch the adjustment mechanism to the other side.

Reading the actual circuits being fused from the little plastic cover (yes, still have mine), I saw that one covered the instruments and turn signals. I've replaced all but two of my ceramic fuses with Buss cylindrical glass fuses with pointy ends...yes, they make them, but they are awfully hard to find... One which wasn't replaced was the 5A in question. It was hoary looking, probably original to the car. When I pulled it out, the metal part fully separated and I knew I had solved my problem. Just didn't catch it on the visual inspection.

That was easy. But without your guys help I bet I would have pulled the alternator and had it bench tested somewhere. Thanks. Now, if i could get the tach to work with my new MSD Blaster Coil, my 1800 world would be momentarily perfect. But that's a whole other thread.

You need an MSD signal generator to get the tach to work with your coil. Part # MS-8910 $38.95 from Summit. I've got one I don't need if your interested.

Mike M.

It didn't occur to me to mention that the same fuse that supplies the turn signals also is
the "hot lead" to the amp light. So if that fuse is blown, the hot side of the amp light is
grounded through the other stuff in the circuit and the charge from the alternator lights it up.
In 1978 I had a chance to buy a very nice 142 with that problem but didn't recognize it.
It was dirt cheap (because of that problem).
If I had bought that car I might never have gotten Li'l Red!

One other thing: Curiously, prior to replacing the Instruments Fuse, when I turned on the ignition the customary red warning lights for charging and oil pressure did not come on. But when I started the engine, the alternator light did come on. Think that's what really threw me off. Can anyone explain that?

Often when odd electrical things pop up, grounds are the culprit.

The light circuit could be the ground for some other load.

I would check grounds.

Older bricks have far fewer ground wires than today's cars.

One of the first things I repaired on my 544 was a reluctant license plate light - no ground wire - a small clip on the light had to ground on the bumper guard, which had to ground on the bumper, which had to ground on its brackets, which had to ground on the car's body, which had to ground to the battery.

All the fasteners had to ground as well!
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 485,000 miles put on 9 bricks