Hi guys,
I drove from Boston to Albany last week (about 4 hours each way) and I was on the Mass Pike and noticed the start of the problem. I ran the headlights all the way to Albany, as it was early. Everything was going normal for the 71 142e that day. Just a nice smooth ride as I sipped my coffee on the way to the Albany office.

Then, I noticed that the tach was acting strange, bouncing up and down- not in sync with actual RPMs. I noticed that the turn signals stopped working as I changed lanes. Hmmm…. I drove on.
Then, the tach came back to normal for a while, and so did the turn signals. I made it to the office and went on in as normal.
I came out after a day of work to find my battery low and weak. I got a jump start with the cables that I carry in my trunk, and she started up just fine.

It was almost dark when I started my trek back to MA. My headlights became dimmer and dimmer, until is was ALMOST unsafe to drive. I stopped at a gas station, and sure enough it would not start after I turned it off. However, it WILL run with the battery disconnected. I got ANOTHER jump and drove on home. When I pulled in, I checked the battery voltage and it was 11.4 volts. This is the reading both WITH and WITHOUT the battery connected. The battery read about 11 volts when standing alone- disconnected.

I thought the battery was bad. I put in a different battery that I knew to be good and it was fully charged from my new craftsman charger. –a 2 day charge on 2 am slow charge.
So, I drove the thing to work today- about 100 miles round trip.
On the way home, I ran the headlights and they got dimmer and dimmer on the way. I pulled into the house and shut the engine off. Sure enough- not enough battery to run it. I believe the situation is as this:

The alternator/generator seems to only put out 11.4 volts- not charging the battery, but giving enough power to ‘sort of’ run the car without a battery.

Can you comment on my diagnostics? Where is my problem?

Thanks in advance guys,

Jeremy
--
71 142E and a yard full of 240's in Mass.

The symptoms sound familiar, as with my '86 240, I neglected to tighten a ground wire on the rear of the alternator while working in that area.

The car was driving off battery power for the 50 miles I managed to drive it before it gave up.

The symptoms soound familiar, as with my '86 240, I neglected to tighten a ground wire on the rear of the alternator while working in that area.

The car was driving off battery power for the 50 miles I managed to drive it before it gave up.

Sounds like either the voltage regulator or the diode/brushes assembly is failing. But before we get to any conclusions, first check if it's got the original setup with a mechanical regulator mounted next to the radiator, or if the alternator had been replaced with a modern one which has a built-in regulator. The original will have 3 wires on the alternator, the modern one will have only 2 wires.

If external mechanical regulator, I've got the procedure for adjusting it if the system otherwise works fine.

And I assume the alternator lamp is working as normal, coming on when you turn the ignition on and turning off when the engine is started? Probably a silly question, but I'm taking you through diagnostic steps.

If the lamp is working, does it go out completely when the engine is running or does it shine dimly?

I suggest you charge you battery at work as well, because the 2 things that kill lead acid batteries is standing directly on a concrete floor and standing discharged.

Hi Neil,
The AMP light works fine, coming on when the key is on, and then going off when the engine is started. It goes out completely when the engine is running. The setup on the car is original, with the mechanical regulator mounted near the radiator.

thanks,
Jeremy
--
71 142E and a yard full of 240's in Mass.

Sorry for the delay in reply, had to work over the weekend.

Normal failure mode for the voltage regulator (relay thing with bi-metal strip) is too high voltage, normal failure mode for the alternator is too low voltage. If the regulator fails, usually the contact do not close any more. If the alternator fails, usually the rectifier to the battery failed but the rectifier to the voltage regulator is still working. But there are exceptions.

The voltage regulator is adjusted by bending the contacts for the bi-metal strip. I can scan the pages in my "green book" if you want, just let me know if it's OK to send you a large e-mail...

(It would be better if someone can point me to a web site where one can upload photos/pictures, because e-mail is really inefficient in sending binary files. And I've got too much to do to spend time searching for a good picture hosting site. Thanks in advance.)

Neil,

The AMP light on my '69 B20B shines dimly. I also noticed it sometimes takes quite a while to go "out" while the engine is warming up. I need to rev the engine to get the alternator to begin charging the battery (which it will at 16.67 volts)


It has an aftermarket alternator (forget what brand) and three wires to it from a moulded plug in a decrepit looking relay on the right side of the radiator (which I thought has omething to do with the headlights?)

What is the dimly glowing AMP light telling me? What is this relay behind the headlight (voltage regulator?)

I have a Bosch 35amp alternator from a '71 142 I could install.

I'd rather get a reliable diagnosis of my problem first.

You might be able to get something adjusting the regulator unless the
charging device (alternator, right??) is shot. But usually that is just
brushes which are easy to change.
--
George Downs Bartlesville, Heart of the USA!