weird goings on 99 expy

[stamp11127]

VR is internal.

What is your charging voltage? And also when the battery light is on? Use the multimeter.
If/when you lose power to the field coil the alternator will quit. Sounds like that is your problem.

 

[Kermit]

That video you had me watch said there is an internal and external voltage regulator stamp. Charging voltage from the alternator at the post has consistently been 14.5. Could you better explain the "if/when you lose power to the field coil" part plz stamp. With your statement there it sounds like you're saying the alternator is no good despite testing saying otherwise...

 

[stamp11127]

There are two types of voltage regulators - internal and external. The older cars from had external, most newer cars are internal. But we can't leave things alone, some manufactures have moved the voltage regulator to the ecm.

"We checked all the connections, cleaned some, made sure we had good contact, charged the battery to 12.9, sat overnight in minus 10° weather, stated right up this morning, gauge read on the high side of the half mark on the gauge, took it on the highway for about 20 miles, battery light on the whole time".

This is why you need to check voltage output at the alternator post and at the battery post. Do you have the same reading at both?

Field Coil: Not saying the alternator is bad, just saying it might be losing power to the field coil. It is just one of a few possibilities, the other is wiring issues. Could be as simple as the plug is shot.

Need to know the charging voltage at the battery and at the alt output post when the battery light is on.

 

[Kermit]

What is this image of? I know the boot is the battery cable but what is the plate attached to the firewall? Hubby says both posts are positive according to reading it with a meter, they both give a reading.

 

[Kermit]

The voltage at the alt post 14.5 and the battery was 12.9 with the battery light on. Coming home last night on the highway, the battery light was on, went off then came back on the rest of the way home. It was after that incident, after using the defogger, that the battery started to drop voltage consistently.

 

[stamp11127]

Starter relay.

Do you know how to do a voltage drop test on the alternator output cable?

 

[Kermit]

I don't, can u run me thru it plz?

 

[stamp11127]

There is a sticky in the electrical section for a YT video from "Eric the Car Guy" that is very informative.

The beauty of this test is you don't have to disconnect anything and you are testing while it is powered. Watch where you run the meter leads so that they stay out of the fan / belt while the engine is running.

 

[Kermit]

After getting nothing from the voltage drop test hubby just gave in and got a new alternator. Seems the problem is fixed for now but need to run the truck more to be certain. Only driven twice since installation and no battery light so far... Now onto the next issue... Rear break line, ugh...

Thanks for all your help guys