I have a 92 f350 7.3 idi , my alt. is putting out 11 volts even when I rev the engine. This is my 2nd alt in about 6 months. The batteries load test good. Do I need a higher amperage alt or why am I going through alts?

 

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Charging voltage should basically be the same regardless of alternator amp spec, say 13.8 to 14.2 not sure what the issue is here but amperage rating of alternator is not it.

11 volts is way too low regardless. The battery cables if original are now 25 years old, that would be one thing to look at, loose, missing or corroded/neglected grounds cable connections.

Even a tiny fraction of a single ohm resistance in the charging circuit will cripple the alternator by as much as a third.

 

That model could have an external voltage regulator. If it does I would do the 3G conversion before I spent a lot money and time trying to fix the existing system.

 

If you have a "1G" alternator with an external regulator, your alternator will have 1 big wire and two smaller ones connected. You will also have a regulator box which is a 2.5" square by 1" tall metal box on the passenger's side, on the flat plate behind the battery.

You also need to make sure that the external regulator is grounded and perhaps replace it.

The regulator has 4 terminals:
I - Needs to have power to it with the key on. Note that if you rewire things, this terminal should be run through a light bulb to power, not connected directly. A tail light bulb works perfectly for this. If you connect it directly to power, the box will overheat and the alternator will also get hot with the engine /not/ running.
A - Goes to the alternator power terminal, or the battery where that power wire ends up
F - goes to the F terminal on the alternator(Field)
S - Goes to the S terminal on the alternator(Stator).

 

I've replaced the external regulator when I replaced the 1st alt. Where should my volt gage be reading? At idle the needle is way to the right by the A on the word normal on the gage. When I replaced the 1st alt the needle was in the middle of the gage and would move higher as I raised the rpms. Then after a few days it went way to the right by the letter A again like its over charging or something. The truck only has 119k miles on it. Looks like original battery cables but don't look that bad. I ordered the 165amp alt to put on it instead of the 100amp. Is there any changes that I will need to do to connect the wires to the 165amp alt?

 

Ah, a hard case. What are you using to measure voltage? It has to be done at the battery posts. Did it come into spec?

Can't tell anything by looking at a cable. A few hundredths of an ohm in the circuit is enough to cripple any alternator. By the time a cable looks bad it has probably failed altogether.

 

When it seems like it is overcharging, check the regulator. I've seen this happen on one of my trucks and it got /hot/. I think it has something to do with the regulator overheating.

I solved the problem by replacing all 4 terminals on the regulator(they were rusty) and checking that all the control wiring was in good shape. It might be worth it to just install new wires from the regulator to the alt, as well as a new power line from the alt to the battery. Also one from the A terminal to the new power line, to make sure it's getting the right feedback voltage.

Note that even a 50a alternator would be fine; the extra amperage isn't really an issue here, unless you are using, like, massive floodlights or something.
The extra amperage only helps when running accessories, and possibly charging the batteries back up after cranking(only an issue if you are doing lots of quick stops with no longer - 10 mile+ runs)

 

What alternator do you have? Test it by jumping +12v to the field terminal, if still nothing it's toast. If you have a 1g or 2d alternator it's a good time to upgrade to a 3g and do new wiring to the alternator.

 

1992 should be 3G, no?

When you turn the key to RUN, does the charging system failure warning light (red battery icon on dash) light up? If not, check that bulb. That's the I circuit (still applies even with the internal regulator) that Macrobb references in post #4. With that bulb burned out, the circuit to trigger the alternator is open.

 

Interesting. Didn't know that the 3g had the same light system. I'll remember that.

 

I bought a used 165 amp leece Neville ambulance alt. I have to swap the serpentine pulley with my 2v pulley. Do I have to by pass the external voltage regulator that's on the fender well to use this alt? How do I wire up this alt? the 1g alt has the main power wire and a 2 wire connector. The 165 amp alt has 1 main power wire and 3 other wires.