Alternator/charging issue

[racer]

I bought a 1987 924S back in July. The car has AC delete (so a less typical alternator placement). On the drive home from the purchase, so some 250 miles into the trip home, the alternator stopped working about 20 miles from home. this was noticed by the dropping charge on the after market volt meter. I continued to drive the car home and as expected, drained the battery enough that the car wouldn't restart.


Put battery on charger. Returned to full charge.

Removed and replaced the alternator with a like model - Bosch AL29X.
Installed a belt (Continental 5K x 736).
Turnbuckle tensioner. Left about 1/2" of slack in the belt as measured in the middle of the belt run.

Went for a test drive. Voltmeter gauge read between 12-13 volts the whole time. 20 mile drive. No heavy electrical use (ie radio, ac etc). got home. Turned off car. car sat 20 min. Went back to move car and in car volt meter read 10 and car wouldn't start. Jumped it from my other car, started right up. Voltmeter crept up to 12+..

got a reading from the battery terminals of 12.6 static. Started the car and got a reading of 13+ (even though the cars volt meter was reading closer to 12.5).

Thoughts?

[racer]

Forgot gratuitous pic. Car is not stock. Previous owner was turning it into an SP2 class 944Cup car.

[thomasryan]

dash bulb and/or check the blue exciter wire at the alt

[944 Ecology]

Bad battery. Have it load tested.

[racer]

Follow up:

1) Took battery to Autozone. They ran a test on it and its tester said "battery is bad"
2) Took battery to Interstate battery store (it was an Interstate MT47/H5 battery). Their tester did not say the battery was bad.. but admittedly, the battery was 5 years old. So, wanting to start a new baseline, I acquired a similar new battery.

New Battery installed.

The car does have a Longacre battery disconnect switch. My process is to use that switch to turn off power when I leave the car. I have noticed sometimes the switch makes a rather pronounced "click" when turning on/off and other times, it feels "soft" when turning on or off.

After new battery was installed, I turned the switch and went to start the car. Nothing. Not a click.. not a starter spinning slowly.. noting. The only thing that happened was the cars voltmeter moved.

Got out of car. Turned longacre switch off and then back on.

Got back in car. Car started right up.
Checked battery.. static 12.6 volts.. while running 13.5 volts.

I am beginning to think that my longacre switch is failing.

Any other over the interweb diagnosis ideas?

[TheSecondChris]

After all the time consuming and costly work you've done already it seems silly not to either remove or replace the switch at this point.

[universeman]

Get rid of the switch. You shouldn't need it if you have a tight electrical system. Install it before you hit the track.

[kdjones2000]

We have had the Longacre switch fail on our race car. Get a new one...