GM 3 wire alternator conversion
 

1986 sr5 with charge gauge and light.
# 1 wire to yellow #1 alt light yellow . start engine
Light goes off but not charging. So
I changed from yellow to red wire on #1
now charging but light stays on. Whats wrong
Thanks Steve.Sense to #2

is it a new alternator?

No But had it tested and tested good?

So far as I can tell, your vehicle has to be (has to have been) rewired to use the dash light with a "3-wire" (CS130?) alternator.

The field wire on the CS130 is "#1", and should be connected to the (originally) red wire to the Engine Fuse. The (smaller) white wire is the Sense wire, so it would go to #2.

The yellow wire goes to battery voltage through the Alt light. It's purpose is to connect to the alternator output, so that when the alternator reaches 12v, the alt light has 12v on both leads, and goes out. According to this site https://www.pirate4x4.com/tech/billavista/Wiring/Part2/, you could use the yellow wire instead of the red wire to #1 to supply the field current. If you did that, of course, the Alt light would STAY ON when the alternator is running. (absent some rewiring).

What alternator do you have? Has your truck been re-wired to accommodate it? (and if so, how?) What voltage did you get at the battery when you concluded "it wasn't charging." (You used your multimeter, didn't you?)

I am getting 14.4 at the battery and same at dash gauge , Light is on I have red wire to # 1 and white to #2 that is the only rewiring done so far, With the yeoole wire not connected
the choke wire is dead. When I had the yellow wire to #1 no light but did not charge. Which way would you hook it up. I thought about using a relay to the yellow wire.

alternator is a 12 SI

Also read somthing about running #2 directly to post on the back of the alternator ?

Alternator is off of my 1979 454

Multi meter yes 12.5