[DeTomaso] Interesting ammeter situation.

[B. SEIB]

Hi Mike
I would try a known good battery and make sure the ground cables at the
battery and the engine are good continuous connections. Wouldn't hurt to
check the continuity of the cable from the output side of the ammeter to the
battery + terminal too. 

If that doesn't change anything I think the new regulator may be the
problem.

If the battery is not acting as a "ballast" to absorb fluctuations in
voltage, the ammeter will show it with behaviour like you've seen. (as in
taking off the positive cable while the engine is running - a VERY bad idea)
My guess is the regulator is not quite up to the job.

Good Luck
Barry
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[DeTomaso] Interesting ammeter situation.
Mike Drew MikeLDrew at aol.com 
Tue Feb 14 22:19:28 EST 2017 

Guys,

Yesterday I accompanied the new owner of a '74 Pantera from Sacramento to
his home in San Diego. 

We almost made it. 

As we entered the worst of the LA megopolis, the charging system suddenly
didn't. The am we had been dancing around for hours and it finally
stabilized deep in the discharge zone. With headlights and fans on, crawling
in stop and go traffic, it wouldn't be too long before the car quit
completely so we dove off the freeway into a gas station and then enjoyed a
two-hour tow truck ride (gotta love AAA premium!)

Today we started troubleshooting. The new owner is almost devoid of tools,
but we started by changing the regulator since its cheap. The result was an
ammeter that now danced violently either side of center. 

Next suspect was the alternator. Although it was new, it was a standard Ford
remain and thus probably only 50A. We took it to a nearby alternator/starter
shop where they rebuilt it and converted to 90A in just over an hour. They
said it tested good beforehand, but since we were there, why not improve it?

With the rebuilt ammeter installed, the needle swing was even more
pronounced, wider at idle, and reducing at about 3000 rpm. 

Now armed with a recently purchased voltmeter, we tested voltage at the
battery and found it cranking out 14.3-14.6 volts depending on rpm and
electrical load (headlights etc)

After a quick call to SOBill Taylor (bless him!!!!) we reinstalled the old
regulator to see what would happen.  

Ammeter jumping stopped, replaced with a constant discharge. Voltmeter
testing at the battery revealed 12.5 volts--the battery was powering the car
and the alternator was doing nothing. 

We reinstalled the new, electronic (as opposed to stock-style mechanical)
regulator, and once again had proper charging indications at the battery,
but the ammeter continued its wild ways. 

I shot a video and stupidly oriented my phone vertically. Only idiots shoot
videos like this, so my profound apologies:

http://youtu.be/lLKf2Z23P_Q

So what do you think the next course of action should be? I have at least
one extra stock ammeter and several regulators, so I am thinking of loaning
them to him for troubleshooting purposes. Do any of you have any
suggestions?

(No, don't suggest he just bypass the gauge or switch to a voltmeter--a
voltmeter would not have warned us of our charging system failure and would
have left us stranded on the freeway!)

Thanks in advance for any constructive advice (other than to learn how to
hold a phone properly when shooting a video!)

Mike