Alt not charging

[85burb]

So i found out my alt on 85 c10 in not doing any thing. All 3 wires have 12v to them. That is not corret is it. The post coming off the alt has 12 and the 2 on the plug both have 12 v. Which one is supposed to have less. Any ideas?

[Gibson]

Originally Posted by 85burb

So i found out my alt on 85 c10 in not doing any thing. All 3 wires have 12v to them. That is not corret is it. The post coming off the alt has 12 and the 2 on the plug both have 12 v. Which one is supposed to have less. Any ideas?

Dude, I feel your pain. Going through the same exact thing right now, except I have 12 on the primary and charge lead, but 11v on the exciter wire.

Some things you may not have checked yet that I've found through my research is:
1) Make sure you clean your ground to the alt and make sure your ground on your fuse panel is clean. "Bad ground somewhere" is apparently the most common cause of this.
2) Take the alt off and take it to your local parts store. They usually check them for free (you don't have to have your vehicle there - just the alt).
3) This one probably is your problem because you said you had voltage on your exciter wire, but be sure to check your idiot light. According to the guy at the parts store, your idiot light is part of the circuit that tells the alternator to through out voltage. Don't know if that is true or not, but it is easy enough to take out of the equation.
4) Clean the contacts on that pigtail really well.

I hope you have better luck than I have!

[85burb]

I took alt to store and it failed every test they gave it. Put new tested on on and it charges 14.5v at batt.

I think that truck has a gauge and not the light so wouldnt that be different. The po halked the cluster all up and put in manual oil psi gauge and temp gauge that is now not working. Anyways could the missing volt meter be the problem? It is charging now but way too much i think. I have heard if they have batt voltage on the exciter wire all the time it shortens the life of the alt. Is that correct?

[Gibson]

I think that is on the high end of the acceptable range, but I think it jumps around a little depending on engine rpm.

I don't know if the exciter wire is SUPPOSED to continue to have voltage or not, but if you find out let me know! I wonder if that is my problem too...
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[85burb]

That 14.5 is at idle. Hoping to find out more myself.

[rfmaster]

Originally Posted by 85burb

That 14.5 is at idle. Hoping to find out more myself.

14.5 Volts is about right for 12-SI (or 10-SI) rebuilt alternator. Most of the alternator rebuilders use a remote sense voltage regulator with set point of 14.3Vdc. As the battery takes charge the alternator output voltage will drop to about 13.6 to 13.8Vdc. Never run alternator without battery connected.

//RF

[Gibson]

I made the mistake of running mine disconnected from the battery - I think I dodged the bullet on the damage though. Details on the dangers can be found here: http://www.troubleshooters.com/dont_...ct_battery.htm
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