Get any service manual, Chiltons, Motors, whatever. Follow the test
procedures. You will need a voltmeter. My Chilton's covers 89 to 91 Dodge
trucks ONLY. It's mostly copies of the factory manual and is well worth the
money. (Part no. 8166.) Got it at Wal*Mart.
An ammeter measures the magnetic field around the wires and gives an
indication based on magnetic field strength, which is proportional to
On my 79, I pulled the bad ammeter out when I measured battery voltage
at 12.7 Volts and the ammeter didn't show any charge. I modified the
dash insert to hold a similar sized voltmeter. I picked up my system
voltage from the connection I made when I joined the two ammeter wires
together( Don't forget to insulate this connection!!!)
To answer your question, yes -- if the ammeter is open, you will get no
charging current into the battery. However, it's likely the ammeter itself
isn't open. Assuming you don't have a factory 100A alternator setup, I'd
start by checking the connections on the firewall where two large wires pass
thru, from the alternator and to the battery. Even a few ohms of resistance
will severely limit the current supplied by the alternator.
At the connector assembly, check connections for the larger two wires that
pass thru there. One comes from the alternator (12ga black), and one goes
to the battery (12ga red). Unplug the connector on the engine bay side and
inspect the terminals -- there should be little or no oxidation and no
evidence of heating. If the connections have produced any significant heat,
the plastic connector housing tends to melt.
http://www.madelectrical.com/electricaltech/amp-gauges.shtml shows this.
If any pins are burned, they should be replaced -- the dealer will have
replacements. If you don't care about keeping it all original, you can
bypass the connector assembly.
http://www.madelectrical.com/electricaltech/amp-gauges2.shtml shows one
method. FWIW, when equipped with a 100A alternator, larger wires were fed
thru the firewall using separate individual connections.
If your connections on the firewall are OK, pull the instrument cluster and
check the connections on the ammeter itself. These are ring terminals, held
onto the ammeter with nuts. I've seen them loosen and cause a similar
current limiting (and heating/melting) issue.
Try to find a wiring diagram. Starting in 1980 the charging
current did not go through tha ammeter. The ammeter was
connected across a portion of the wire between the alternator and
the battery with a couple of about 20 gauge wires, effectively
using the feed wire as a shunt for the ammeter. An open ammeter
will make no difference. A more likely area to look at is either
of the two heavy plug type connectors in the 6 ga wire between
the alternator and the battery or the 14/12 ga fuse link in the
The easiest way to check this would be to measure voltage at the alternators
output terminal with the engine not running. If you get no voltage reading
then you have a failed connection or fusible link on the output side. If
you do get battery voltage, I would then put some type of load on that
connection (like a headlight) and measure it again. If you still get
battery voltage or within 1/2 a volt of it, then the connection between the
battery and the alternator output is fine and I would start looking at the
regulator and field wiring as your most likely cause of your problems.
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