Alternator question, more of a sanity check

[lostintexas]

Read the 15 pages in the stickies and think I know what the issue is but wanted to run it by the resident experts before I got too far off course. I have an '86 M1009 that was converted to a pure 12v system before I got the truck. That being said the charging system had been doing good until recently. I had added a voltmeter in place of the dummy light and that's when I think this dummy caused the problems. Well I replaced both batteries at the same time then ran into issues with the injector pump. Long story short that was over two months ago and finally got the IP going again now on to the charging issue, or lack of charging issue. Batteries are still producing 12.1v and cranking the truck but voltmeter is reading ~12v when cranked. Doing the checks the exciter wire is not getting power when the key is on. My thoughts are that when the dummy light was removed the circuit was broken for the exciter wire (brown with white trace). I can take a jumper and apply 12v to the exciter and the voltmeter starts to climb to 13.9-14.1v. This makes me think the alternator is working and it's just not getting activated to start charging.

My questions:
1) Does the logic sound right with the circuit being broken with the removal of the dummy light?
2) What if I tapped into keyed power to use as the exciter wire? Any issues with that?

Thanks guys, hoping for an easy/cheap fix on this one.

 

[Warthog]

Because of the design the idiot light has to be in the circuit. Without it the alternator will not excite.

 

[lostintexas]

Thanks Warthog for confirming my suspicion. Shouldn't be too bad to get it back right.
L.I.T.

 

[Warthog]

While some of this is technical it will give you a basic understanding of the alternator. Read the Basic Operation.

 

[M1008driver]

My M1008 is converted to 12 volt using the roscommon method. I did this because I use it hunting in sometimes remote places and wanted to be able to buy parts locally. Since then my truck has never let me down.

You wrote,"That being said the charging system had been doing good until recently. I had added a voltmeter in place of the dummy light and that's when I think this dummy caused the problems."

Yes, I think it did cause your problems. Before I do a project I study it, research the idea on the forum, take a cup of coffee and stare at my truck thinking it through. If I do not understand I study some more. I guess what I am saying is slow down and get it right the first time to not have problems later. Peace!