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Old 07-03-2010, 10:18 AM
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Alternator issue?

Well I had my alternator tested and they said it was god went right to 14.5v

Car died a couple times lastnight downtown and crap. My alternator has 2 blades on the top and a post on the back. Can someone tell me where theyre supposed to go? I have the wiring diagram but it makes no sense.

Someone said one of the blades needs to be grounded or something but I have no clue.


I currently have I think the #2 terminal wired to the back post and the back post goes back to the battery. Nothing on terminal 1 anymore.

After doing some digging around... I found a diagram:

http://www.derbypro.com/goldmember/pics/alt.gif

1. This is the main power wire that goes directly to the battery. Make sure it is a heavy gauge since it has to carry the full output of the alternator (up to 100 amps).

2. This is the field wire that energizes the alternator. It must be switched, or else it will drain the battery overnight. Do not wire this into the coil power wire that you use to switch the engine on and off (a seemingly elegant solution), since once the engine is running, the alternator will power the coil, and your ignition switch will no longer kill the engine.

3. This is the lead for the sensing wire that goes to the idiot light in your instrument panel. A neat tip: if you aren't using a voltmeter or oil pressure gauge, run this wire to a light mounted somewhere on your dash. Often you can't hear your own engine running in the derby, so when this light lights up you know that your engine has just quit (or the alternator has just stopped charging for some reason).

4. This is the regulator bypass hole. Sticking a long thin metal object about 2 inches deep into this D-shaped hole causes the alternator to go to full charge. If you do this while it's dark out and the main power wire is disconnected, the whole alternator will emit a cool X-Files type glow. I don't recommend that you try this since you'll likely end up frying your alternator.

Could not having a switched source field wire stop it from charging? The way I read it, the alternator wont energize without it?

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Old 07-03-2010, 06:42 PM
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Quote:
Originally Posted by 84TA406
Could not having a switched source field wire stop it from charging? The way I read it, the alternator wont energize without it?
Sounds like you have an "SI"-type GM alternator, if so, the statement above is correct.

From HERE:

"The ignition wire to the #1 terminal can be supplied in two ways, either a direct ignition wire from the key switch or through a light bulb. Running the ignition wire through a light bulb before connection to the alternator will give you a warning if your alternator fails to start charging or if it quits working while the engine is running, this is commonly known as the idiot light. Another thing that should be mentioned is the #1 terminal must be ignition switched. I have heard of situations where a wire was run to the #1 terminal that had power on at all times. What happens is when the engine is turned off the #1 terminal switches to ground which over time can burn up the voltage regulator or the wire if power is not cut to the #1 terminal. Another note for special installations of the Si series alternator is that in some cases when you try to shut the vehicle off, power to the #1 terminal from ground to positive power, the positive power feeds up to the coil and keeps the vehicle running. To cure this you must install a diode in the ignition wire that activates the #1 terminal. The diode will stop the power from feeding back up the ignition line."
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Old 07-04-2010, 07:34 AM
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Ok my other question is everywhere says terminal 1 but I looked on some cars yesterday and a lot had a heavy red wire coming off terminal 2. Is that a diffrent alternator or am I missing something?
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Old 07-04-2010, 12:57 PM
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You might be getting terminal 1 on the alternator (which is the spade connector on the left, as you look at the back of the alternator) confused with the what they called number 1 on the derbypro picture.

BAT terminal (threaded post) is connected to constant 12 volt battery power. This is your charge wire.
Term #1 - (excitor, left side of space) connected to the ignition switch
Term #2 - (sensing, right side of spade) either jumped over to the BAT terminal, or connected into a junction in the vehicle

Term #2 works best if it can sense the voltage drop and adjust the alternator to compensate, however, it will also work with a simple jumper to the BAT terminal.

Bruce
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Old 07-04-2010, 09:52 PM
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Thanks man, I'm going to hook it up just like you explained. If it doesnt work I'll swap to a 1 wire.
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