Hey All,

Helping my son work on his GT and hoping for some help. We had a series of events (dead battery, new battery, new battery dead) that lead us to picking up a new alternator. My son was putting the new one in and didn't pay attention to where the wires were going at first and ended up hooking the big red wire to the D+ port the first time we fired it up and tested it. We noticed the battery was not charging so I dug into the wiring and realized the mistake. We then moved the big red wire to the B+ terminal and the small red one to the D+ terminal. The car starts up but is not charging. I test voltage on the D+ terminal and get ~1 volt when the key is in the 2 position and ~6.6 volts when the car is running. Did we ruin the new alternator with the first round of wiring or is there something else we should look at?

Thanks for your help!

Nathan

 

You did not mention the third wire - A 240 alternator is mounted in rubber bushings - so there is a ground wire attached near the bottom of the alternator to the engine block - Is that attached? Without the ground wire - the alternator will not charge.

 

Yes, sorry I didn't mention that but the ground wire is installed.

 

Since both outputs are 12-14V I don't think any damage was done.
I would hook everything up correctly. Turn the key on and measure the voltage at the small wire output. It should be 12V. If not check fuse 13. If ok try to start the car, and see if everything works.
If not measure voltage at both the large and small outputs. Both should be 12-14V.

 

Does the battery light on the dash light up when you turn the key to the II position (engine not running)? This bulb needs to be functioning in order for the alternator to start charging.

 

There is nothing in the car's charging system that could produce negative voltage unless something is hooked up in reverse like the meter or the battery. Even if the meter or battery grounds are different the meter might read low but not negative. Both grounds should be connected directly to the car's body for the most accurate measurements.

The engine block must also be connected to the car's body for a complete circuit.

 

Where was negative voltage mentioned in this thread?

 

Finally got to do some more testing last night and figured out the AMP light does come on with the key in the II position and also stays on when the car is running. Bad alternator then?

 

Yes ---

 

I'm confusing this thread with a similar one on Turbobricks. Also the ~ for -.

 

Yeah, I started here but wasn't getting much traction here so I went back to my trusty TBricks and got more engagement. I can probably just delete this one but didn't want to abandon it because people had responded and I want to respect their time.

TB Link: https://turbobricks.com/index.php?th...arging.377564/

 

This is not true on all models. I have a 1986 volvo 240 that recently kept dying as well, and the battery light has not turned on and never does, even now that it is fixed. I checked the bulb, too, and the bulb is good.

Turned out the remanufactured alternator I had purchased was not good. Also, check the back of the alternator and make sure that there is a little coil thing attached, that can help manage voltage spikes or whatever. Also a slightly slipping belt may undercharge your battery. Make sure it's TIGHT, like so tight you can barely get the belt on and almost no give when you press on the belt.