1998 Pontiac Grand Prix po560

You appear to have a bad battery. The koeo voltage should not drop that dramatically. A bad battery can make the alternator do strange things also so I would replace the battery and check your voltages again.

the battery is new battery voltage with engine off is 12.3 why does my orange wire at the alternator only have 10.65 this should also have12.3 right???????

Yes, it should. There is a fusible link between the alternator and the battery that may be bad or you may just have a bad connection somewhere.

where is the fusible link should I run a new wire from the sense fuse to the alt.

Sense fuse? I though you were reading the output terminal.

the voltage at the sense fuse is 12.3 and the voltage at the orange wire at the alternator is 10.65

I don't know what color the wires are. If the main terminal doesn't match battery voltage, you have a problem in that circuit. The fusible link is probably at the starter.

u are telling me info I already know I need help finding the problem can u look at a wiring diagram and give me some good info if u need more info on my end just ask

Check for the following conditions: Poor connection or damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the Ignition 1 voltage display on the scan tool while moving connectors and wiring related to the PCM, dash harness, and engine harness. A change in the display will indicate the location of the fault. If DTC P0506 cannot be duplicated, reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition. The orange wire runs from the fuse box to the PCM and the code is telling you the voltage is incorrect. Find out why. Does the fuse match the battery voltage? Maybe an issue with the fuse box or wiring.

the fuse voltage is correct and the #20 orange wire at the pcm has the correct voltage I don't understand where the orange wire at the alternator gets its voltage --if I unhook that orange wire at the alternator my engine running voltage falls into spec

should the orange wire at the alternator be hot at all times when I turn the key off I lose voltage at orange wire at the alternator but it stays hot at the -pcm when I unhook the orange wire at the alternator and jump to b+ everything works normal

The orange wire at the alternator should be hot at all times. It is powered by fuse #10

be back on Monday am will text more info then thanx for all the help

You should be able to resolve it with the info you have.

there is no fuse #10

According to the wiring diagram, it should be hot at all times.

the ecm sense fuse is hot at all times with correct voltage with key on voltage at orange wire at alternator is only 10.65 with key off it goes to 0

The first diagram was for a Grand am not Grand prix but here is the correct one and that feed is the same. That fuse should be hot at all times.