Question About Alternator Test 1969

[Lawrence M.]

1969 small block . Believed to be original 42 Amp Alt. Probably rebuilt in early 90's when car was restored by PO.
Want to make sure an internal problem with the Alt is all I have.
Key off voltage at battrey is 12.75
At idle voltage at battery is 12.75
Key on Alt Bat Terminal shows 0.155 volts
Alt Harness terminal 1 shows 0.08-0.10 volts
Alt Harness terminal 2 shows 12.75 volts
At idle Alt Bat Terminal shows 76.2 volts ! Checked with 2 multimeters. Apparently non of it getting to the battery.

I want to make sure this doesn't indicate more than an internal problem with the Alt.

Also did a parasitic draw test. 00.48 milliamps.

Thanks for any advice.

[Jimmy G.]

Re: Question About Alternator Test 1969

Alternator or the regulator is bad Voltage at idle should be north of 14

[Joe L.]

Re: Question About Alternator Test 1969

1969 small block . Believed to be original 42 Amp Alt. Probably rebuilt in early 90's when car was restored by PO.
Want to make sure an internal problem with the Alt is all I have.
Key off voltage at battrey is 12.75
At idle voltage at battery is 12.75
Key on Alt Bat Terminal shows 0.155 volts
Alt Harness terminal 1 shows 0.08-0.10 volts
Alt Harness terminal 2 shows 12.75 volts
At idle Alt Bat Terminal shows 76.2 volts ! Checked with 2 multimeters. Apparently non of it getting to the battery.

I want to make sure this doesn't indicate more than an internal problem with the Alt.

Also did a parasitic draw test. 00.48 milliamps.

Thanks for any advice.

Larry------


Can you post front and back photos of the alternator?

[Lawrence M.]

Re: Question About Alternator Test 1969

Joe,
I will be removing the Alt tomorrow, and will take the pictures for you . The car is a late build (Q15) with a "900" alt, date code 9L21.
Thanks for the replies Joe and Jimmy.

[William H.]

Re: Question About Alternator Test 1969

Hello Larry!
Your Alternator may not be bad. You seem to have an open between ALt bat teminal and battery. I don't have a 69 wiring diag handy but at the alternator battery terminal you should read battery voltage with the key off or on engine not running. THen about 13-14.5 V with the engine at idle or just above. THe alternator is putting out that high voltage because it is not seeing anything back to the regulator in the alternator. THe alternat0r could be bad too. I would find a wiring diagram or look in the shop manual and see how the alt bat terminal gets to the battery. I THINK it is at the horn relay. you may have a blown fusible link or the wires are not connected to the horn relay properly. or the wire from the horn relay to the starter bat terminal may not be complete. I would check all that before replacing th4e alternator. OF course you can take it off and take it to Napa and have them test it. Let us know what you find.
Bill

[Dick W.]

Re: Question About Alternator Test 1969

Hello Larry!
Your Alternator may not be bad. You seem to have an open between ALt bat teminal and battery. I don't have a 69 wiring diag handy but at the alternator battery terminal you should read battery voltage with the key off or on engine not running. THen about 13-14.5 V with the engine at idle or just above. THe alternator is putting out that high voltage because it is not seeing anything back to the regulator in the alternator. THe alternat0r could be bad too. I would find a wiring diagram or look in the shop manual and see how the alt bat terminal gets to the battery. I THINK it is at the horn relay. you may have a blown fusible link or the wires are not connected to the horn relay properly. or the wire from the horn relay to the starter bat terminal may not be complete. I would check all that before replacing th4e alternator. OF course you can take it off and take it to Napa and have them test it. Let us know what you find.
Bill

Blown fusible link would shut power off to basically everything. Believe he has a bad regulator

[Lawrence M.]

Re: Question About Alternator Test 1969

Blown fusible link would shut power off to basically everything. Believe he has a bad regulator

Everything still works. Even the ammeter. Starts and runs fine.

[Lawrence M.]

Re: Question About Alternator Test 1969



Joe,
Here are the pictures you requested.

[Lawrence M.]

Re: Question About Alternator Test 1969

IMG_0382.jpgIMG_0379.jpg

Joe,
Here are the pictures you requested.

[Joe L.]

Re: Question About Alternator Test 1969

Larry------


This appears to be legit very late 1969-1970 alternator configuration. The rear case half would be correct only for very late 1969 which your car apparently is. Note the raised boss for the ground lug and the slightly raised rectangle below the Delco-Remy script. These features are usually associated with 1970 alternators. However, very late 1969 used it, too.

[Lawrence M.]

Re: Question About Alternator Test 1969

Larry------


This appears to be legit very late 1969-1970 alternator configuration. The rear case half would be correct only for very late 1969 which your car apparently is. Note the raised boss for the ground lug and the slightly raised rectangle below the Delco-Remy script. These features are usually associated with 1970 alternators. However, very late 1969 used it, too.

Thanks Joe, The car's build date Q15 is Monday Dec 15, 1969 . The last week of 1969 production.

[Lawrence M.]

Re: Question About Alternator Test 1969

Wanted to post an update on my alternator problem. Sent it to Ken Bruno Motorsports . From the day I shipped it until it arrived at my door was just under 4 weeks. It looks brand new and charges 14.6 volts. Ken also restored my starter last year and it also came out like new and works great.


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