3 new alternators charging 18+ volts???

[hotrob610]

I have a 2000 gmc k2500 with the 5.7 engine. It has dual batteries. I have just replaced both batteries and the alternator 3 times. All 3 new alternators have been showing 18+ volts on the voltmeter with the tester leads on the battery posts. If I put the leads on the alternator, it is showing 20 volts. I am assuming that the voltage regulator is internal within the alternator. The battery light in the dash comes on at higher rpms while the gauge is showing around 10 - 12 volts. Usually closer to 10. The second alternator I returned to the store tested good. Is there something that could be causing this high voltage reading on my volt meter. (Tested the volt meter on two other vehicles and showed fine)

[MikeNH]

The reman alternators can be really crappy. It took two or three in my Jimmy several years ago.

[hotrob610]

UPDATE: I have now used 4 alternators with the same results. What I have noticed is that 2 wires of the plug have been deliberately cut off. I assume this was done when the dual batteries were installed and the truck was set up for a plow. I found out that the newer gm alternators use a two wire plug. Does anyone know if this is contributing to my issues?

[barry G]

my 96 uses all four.

cutting to two is like a 1970s hot rod.

you'll have to set the tickler yourself.

some claim the light in the dash does it all.

 

there is diagrams everywhere.. hot rod related.

2 wire is hack job.

 

the four wire form 96 onward was actually a claim to fame.

the first alternator to actually change loads dynamically.

 

around that time, chrysler had just come out with amonster for the mini vans.

the world has been happy ever since.

 

the old body rotters had a set tickle.. too much at one end, and dying at the other in demand needed.

 

I'd find a way to fix it if you can.

 

the last problem you may have, after getting it right.. once a regulation goes way up, it may not come back down for along time or if at all.

you may need alternator #5.

kinda like computers, or springing a spring..

analogy.

[teamzr1]

Most GM vehicles have a control circuit out from the PCM which commands if and how much the Alt outputs

This is done to reduce engine load for bit better fuel mileage

 

If the PCM in the vehicle has a F and Y terminals ( 2 wires) ( can be seen by using a OBD-II scanner) the also the ALT for that vehicle

would have the logic for this and if wires are not connected then that design ALT will output max voltage and cannot adjust down

 

Locate a service manual and see if your vehicle was designed for ALT commanded by PCM as that dictates how voltage is or is not regulated