ALTERNATOR and volt gauge wiring

[TURBOPOWERED68]

"On the 86/87 the main post has 12v all the time. The little brown wire has ~2.5v when the key is on.

On both alts, the idiot light works the same. The idiot light circuit applies to the number 1 wire(Small) on the 84/85s. When the Alt. is not spinning or not charging, that regulator terminal is a GROUND. When the alternator is charging it is a positive. Two positives DON'T complete a circuit so the light is off
Thanks to http://www.gnttype.org/techarea/electrical/alt.html"

So I can use the Brown wire from the Alt as a trigger onto a relay to turn on my volt gauge.
If I wire the volt gauge to the battery I won’t know of a problem until it’s too late.
Using the brown wire off the alternator as soon as the alternator stops charging I will have a dead volt gauge
And when working I could still wire the volt gauge to read the voltage from the alt main post.

Ok guys what do you think about this idea?

 

[salvageV6]

The relay coil will draw current off the brown wire to trigger it, that is the field wire also, I wouldn't do it but it may work okay if I understood how you were going to wire it all up.

Why not a LED gauge off the alternator large post, triggered 'ON' by an IGN switched relay, when it drops to 12 volts while running the car you know you have a problem, use a flashing red LED for anything below 12 volts.

That will get your attention.

I just cycle through the scanmaster while driving since volts is before water temp. which is what I usually monitor I check that as well once or twice while driving.

I just wouldn't take the chance on messing up the electronic regulator/field control circuit with a relay draw off it.

 

[Chuck Leeper]

Why not just hook the voltmeter into a switched, 12V source?? What's the need for a relay?
+ side to the hot wire, and the other to ground.

 

[TURBOPOWERED68]

Why not just hook the voltmeter into a switched, 12V source?? What's the need for a relay?
+ side to the hot wire, and the other to ground.

because by the time to meter starts to drop you are ready to get stuck.

 

[salvageV6]

Perhaps try a high brightness LED (with proper resistor) off the lamp circuit should only draw 20ma tops and when ON you know you're charging.

About 5-10 times less draw than a typical automotive relay coil.

And put the voltmeter on an IGN circuit where it belongs, or direct to the battery/alternator large post, with IGN switching of a good relay.

I may try that LED trick myself to see what happens, in the spring.

 

[Chuck Leeper]

??

because by the time to meter starts to drop you are ready to get stuck.

Huh? maybe if one keeps an eye on the dash, that, overheating, and no oil pressure, would also be noticed...
Not to mention, maybe avoiding a speeding ticket.

 

[salvageV6]

The solution is to properly fix the brown wire field circuit and it's various connections, so it's not intermittant.

However the LED or a temporarily hooked up high impedance voltmeter on it might be a good diagnostic tool.

I usually use my headlights or the scanmaster on volts for that.