The alternator should put out over 14.0V when the engine is over 2000 RPM.
If the voltage bumped to 8.5V then either a number of battery cells are
shorted (very unlikely to have more than one), or the alternator is bad. Did
you measure from chassis ground to the plus on the second battery? If so
then measuring each battery would produce about 3.5-4V. Are your battery
connections clean? Is the connection to the chassis renewed?. I would remove
all connections and clean and apply Vaseline to prevent oxidation.
If each battery is less than 4Vafter charging, my guess is that the
batteries are toast. Try charging again after cleaning connections. Charge
for 24 hours then retest. IF still under 12.8V total, the batteries are in
for replacement. Personally, I will stick with two batteries. More lead =
more starting power, even if the cold cranking amps are similar. The cost
just doesn't justify the swap in my opinion.
If batteries after cleaning and charging are > 12.8V, then start the car and
rev to over 2000 RPM. The voltage should rise to between 14.0 and 14.8VDC.
Still OK? Then alternator is probably working. (Only way to tell for certain
is to put a dead battery on the alternator with a ammeter in-circuit and see
if it will charge about 60 amps --my '69 MGB spec-- ). I would take the
batts to a repair shop and have them put their "load tester" on the batts.
This will tell you whether you need to replace them or not.
'69 BGT mona
----- Original Message -----
From: "Dave" <firstname.lastname@example.org>
To: "Larry Dickstein" <email@example.com>
Cc: <firstname.lastname@example.org>; <email@example.com>;
Sent: Sunday, April 09, 2000 7:03 PM
Subject: Re: radio sings the blues-test done
> Hi Larry!
> Hope you had a great weekend. Nice weather here in Omaha and took out the
> for about 30-40 miles with the top down. Drove great, ran great. No sign
> the radio noise.
> regarding the test, it looks like the end for the twin 6 volt batteries.
> tested at 7 volts. I put a trickle charge on them for about 6-7 hours.
> luck. still tested at 7 volts. I then cranked up the engine (very slowly)
> because its a good starter, it fired up. the voltage bumped to about 8.5
> which tells me the alternator is ok. drove for the 30-40 miles in town
> shutting it off). got home and retested. same results with engine off - 7
> not sure how this relates to the radio noise but it does tell me why when
> headlights have seemed dim and why, when cranking, the starter seems to
> then slightly diengage while cranking...not full voltage to keep the
> engaged ( I guess).
> anyway, I did check the antenna to the radio as Paul Hunt suggested.
> tight. did not check the small coil wire yet. but again, it did not do
> today. I did replace the hazard light switch and fan switch but don't
> thats any relationship.
> so now I think I'll replace the batteries. thinking of eliminating the
> volts and going with 1-12volt as I have read others doing. would you
> this? if so, where can I find instructions for doing so? and, of course,
> size would that 12 volt be?
> I have copied Paul Hunt, Harlan Jillson and Tim Economu on this since they
> originally responded to my first message as well. any input from any/all
> guys would be appreciated when you have time.
> have a good week!
> Dave Ciaccio
> Larry Dickstein wrote:
> > Dave wrote:
> > > Was driving the '74B sunday when all of a sudden a fairly loud whine
> > > came out of the radio. At the same time the "fasten seat belt" light
> > > started to glow. sounded like it was trying to buzz too. I notice
> > > noises got louder with higher engine revs. sounds to me like some kind
> > > of voltage transfer. before I pull the radio, I thought I would check
> > > out the advise of the list. I have only owned this one for 4 months
> > > never heard this noise. All other electrics seem fine. Any advise is
> > > appreciated!
> > >
> > > Dave Ciaccio
> > > '74B
> > > '76B
> > Dave-
> > I think the radio whine was a symptom but not the cause. My guess
> > be a malfunction in the alternator/voltage regulator. It wouldn't be
> > adviseable to run it in this condition long but a fast check of voltage
> > the car running should tell you the story. If the battery is up the
> > w/ the car not running should be 12+. The high normal voltage w/ the
> > running should not be over a high 13 or low 14. Your observation that
> > noise increased w/ rpm is the key and a good observation on your part.
> > --
> > Larry Dickstein
> > Lone Jack, MO
> > Pop. 420