Alternator wiring diagram needed?

FLORIDAGUY863

MEMBER
1984 CADILLAC SEVILLE
4.1L
V8
2WD
AUTOMATIC
94,000 MILES

I have the car listed above which needed a new alternator. I pulled the old one and installed the new one. On the old alternator it has a two spade/wire clip that pushes on and a red threaded stud and nut with two wires on it one of which runs directly from the pigtail of the clip mentioned above and the other runs to the battery positive terminal. The new alternator is exactly the same as the original. The only difference is the red threaded stud on the new one is black. I got the alternator installed and hooked up the wires in the exact orientation they came off of the original and fired up the car. The alternator is not charging. None of the wires associated with the alternator are original. So, my question is where are these wires supposed to come from?

Thursday, August 24th, 2023 AT 7:15 AM

1 Reply

STEVE W.

MECHANIC
14,067 POSTS

A system from a simpler time. First grab a test light. Now verify it works. Next check that there is battery voltage at the large battery terminal on the alternator. Now with the key Off check the other 2 wires. One should have battery power and the other should not. The one with battery power (OE color orange) goes to terminal 2 on the alternator, which is the sense line and on some it goes to a splice into the interior and on others it just follows the battery feed cable over to the battery positive post. Either way it should have power full time. Now the second wire (OE color Brown) should have battery power only with the key on, and with the key on but the engine not running it should light up the charge lamp on the dash if you use the test light on it (both should light up) Now if the test light and dash light don't come on a blown dash lamp bulb could be the problem as it does a couple things, When you first turn the key to on it sends voltage to the alternators regulator and tells it to turn on, then once the engine starts there should be voltage to that terminal and that turns the light off. The blown bulb causing the system to stop charging is common.
A way that you can do a test on the alternator itself is simple. Take a short wire and jump from the battery terminal to terminal 2 and connect the test light there as well. Start the engine and touch the test light probe to terminal 1. If the light stays off it's working. To verify that you can connect a voltmeter across the battery, then start the engine and use the test light on terminal 1. You should see the meter go from battery voltage up to about 13-14 volts if the alternator is working.

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