Originally Posted by RichardJ (Post 8910572)

>>"flash the field"<<

An interesting term to use when you are talking about an AC Alternator.
If we were talking about a DC Generator that term would make more sense. When discussing a DC Generator, someone will always mention Polarizing the Generator.

In the first image below there are Iron Pole Pieces used in DC generators, The Field Windings are wrapped around these Pole Pieces.
These Iron Pole Pieces retain a great deal of magnetism. The Polarity of the magnetism retained in these pole pieces is crucial to the correct operation of a DC Generator.
When working on a DC Generator, it is common for the polarity of the residual magnetism to be reversed.

It is then very important to correctly align the magnetic polarity of the pole pieces, with the Polarization procedure.

AC Alternators do retain some residual magnetism, but the polarity is not an issue.

In the second image, the ignition switch connects 12V from the battery, through the voltage regulator, directly to the field winding. Full Field magnetism is generated and current begins to flow in the Stator Windings. This ignition circuit is called a Exciter Circuit.

Full Field magnetism is generated the moment the key is turned ON and also at idle. Field magnetism is reduced by the voltage regulator, as max voltage is reached.

Originally Posted by RichardJ (Post 8910579)

>>The theory behind this is a perfect wire with perfect connections will not drop voltage so the meter will read zero volts.<<

All copper wire has resistance to electrical flow. The fatter the wire, the less resistance, the lower the voltage drop from one-end-to-the-other.

Chevy relies on that voltage drop on the wire between the Alt and the Battery. That is the basis of the design of the Ammeter circuit.
The greater the Alternator output, the greater the Voltage Drop on that wire, the greater the Ammeter indication.

The type of Ammeter used in these trucks must have an External SHUNT.
In this case the Charging wire serves doubly duty and is also the Shunt Wire for the Ammeter.

Other Ammeters contain an Internal Shunt. This '67-72 Chevy Ammeter does not.

Originally Posted by HO455 (Post 8911165)

Hopefully the OP will be able get things back to normal.

Originally Posted by RichardJ (Post 8911384)

What is wrong with that?

Originally Posted by RichardJ (Post 8911446)

Unless you have a high load at idle, it doesn't sound like the new 12SI is working properly.

Originally Posted by Steeveedee (Post 8912129)

That seems to be a common problem with rebuilt stuff these days. I've replaced the rebuilt alternator on my truck twice, now. Both times for bad diodes.

Originally Posted by Minkota (Post 8912244)

Mine was supposedly a Brand New Unit, which is why i was thinking it was not the alternator at first.

Originally Posted by Minkota (Post 8914754)

Since installing the new alternator, i am experiencing a pretty bad battery drain. is it possible that it is from the way it is wired?

I connected the 2 outside blue and brown wires at the regulator.
I connected the 2 wires at the alternator plug (previous owner made them them the same color wires black) and connected both of them to the White wire on the ne 12si plug. I feel this might have been wrong.
I ran a new 10ga wire to the battery from the the big red bolt on the back.
I ran a new 10ga ground wire from the alternator housing to the ground on the battery.

Originally Posted by LNP (Post 8914847)

I went with a 100amp one wire alt. This made things simple.

Originally Posted by MARKDTN (Post 8907187)

I would do a couple of things in your situation. I would get rid of the factory ammeter and go to a voltmeter. I would change to a CS144 (I would not use a CS130 as a paperweight). Delco #8077 pigtail is used if you have a lamp on the dash and the #8078 has a load resistor for use with no lamp to go from SI wiring to CS so you will have to do some adapting(different plug at alternator, but can use the same sense wires). Application for a 140A CS144 is '95 Buick Roadmaster. Then I would add a bigger wire from the alternator output to the battery. I might also add a junction block near the battery to power the fans and amp, that way you don't add any high loads to the original harness. While I was wiring, I would add headlight relays as well (to get brighter headlights and take load off the original switches and wiring).

If you don't want a CS144, then a 12si in either 78A or 94A. Anything bigger may have cooling issues. The 84-85 Corvettes do have a 12si that is 120A, but I would go CS144 if I wanted over 100A. 94A 12si is Delco 321-269 application '85 Riviera with 305Y, HD cooling and a/c. 78A 12si is Delco 321-244 application '85 Cutlass Supreme with 305Y. Nothing wrong with a 10si, I would just get a 12si if I was making the change since they have improvements. Don't use a 10si fan on a 12si, you have to get the 12si fan so be sure what you buy has the fan on it.

Originally Posted by xs-cash (Post 8914856)

Where did you hook up the one wire?