Im trying to wire up my Amp guage thats in my dash. One wire went to the horn relay and the other to the positive side of the battery. I turn on the lights and it reads a discharge value, But when I start the car it never shows a charge value alwas a discharge. If I shut the lights off the guage almost goes to 0. I use a 1 wire generator straight to the battery terminal. Just for testing we pulled up another chevelle with the 3 wire alternator. I ran my wires over to his car. I wired it the same way and it worked fine. Showing charge and discharge value. So How do I modify my installation to my system so it can show charge and discharge value?
There's your problem....
The factory ammeter needs the factory designed wiring layout to provide the proper voltage drop.
The original alternator's output wire ran to the junction of battery wires at the horn relay. The relay's buss acted as the main distribution for power.
The ammeter looks at the potential difference (very small voltage) between the horn relay and the junction block behind the battery (which is connected to battery (+) terminal.
By you moving the alternator output right to the battery + lug, you have upset the balance and therefore it will never work as designed.
As a further note , this are used as rough indicators only. It should stay close centered at zero or slight hair into the + zone. Swings into the discharge zone (battery junction higher voltage than horn relay) and swings into the charge zone (horn relay higher voltage than battery junction) indicate problems as there should not be that great of difference between the two points unless there is a problem or the system is being pushed to its design limits.
It's a catch 22 for most. If you want to take advantage of a higher power alternator for more added on goodies, you need to change/bump up wiring gauges, THEN your factory ammeter does not function properly.
As many know, I am not a fan of 1wire alternators. But that's enough typing for tonight.