Re: wiring questions

Posted by BigKev On 2008/9/4 20:52:28

Not sure that is true about terminal 2 (Voltage Sensing Terminal) on a GM 10SI alternator. If just did a quick look through the various diagrams on the aftermarket wiring company websites, and I also looked at the factory wiring diagrams for several 1970's GM cars, and they all have terminal 2 hooked to a always-on 12v source.

Most people just bridge the terminal 2 to the batt terminal. Why this will work, it is not recommended. The purpose of Voltage sensing wire is to get the actual voltage reading from the main harness. The voltage at the alt batt terminal, or the battery itself may not be representive of the voltage at the main harness junction due to wire resistance because of wire length, connections, etc. The main harness junction is where GM connected the voltage sensing wire. Which was a constant hot 12v source.

Now that being said, there is nothing wrong hooking it up to switched source as you have described. I just drew the diagram based on the GM application.

I now remember why I have the dash light wire to the ACC positon instead of the ON position. There are some instances where the Alt can feedback through the dashlight circuit and keep the igntion circuit active, after the key is turned off. Most aftermarket harness companies (Painless, Ez-Wire, etc) recommend using a diode on that wire to prevent that feed back. I thought it would just be easier to hook it to the ACC side of the switch. The downside is that the GEN light will come on when the ignition is left in the ACC position. But then again that could be a good warning that you left the key in that position.

Hope this all makes sense.