12 SI Alternator connections

[COKE]

Hi everybody

My 12 Si alternator started to do strange things such as charging only when i was climbing until one day stopped to charging anymore.

I removed it and checked the resistances on the stator, rotor etc.
Everything seemed to be ok so i ordered a new regulator,diode trio,brush holder with new brushes and also the rectifier.
Everything is from the Standard brand.

I mounted it and it continues no charging,so now i don,t know if the trouble is in the new parts(I don,t like the Standard brand very much) or in other part of the charging system.

The SI alternator has a connector with two wires on the top.One of them is red and supliees 12 volts all the time,that i suppouse that will be for exciting the ALt?The other one is a black wire wich i don,t know where it goes.Woul like to check if this is ok.

Thanks in advance

 

[diesel4me]

If its a pre-1987 style altenator,those 2 smaller wires on the plug do provide 12V to excite the feild coil ,(the red one is always "hot" and the other one that is usually white or tan,but I guess is black on yours,goes to the ignition switch so it only gets power with the key "on"...)............................................................................................

If those wires are not both getting power,the altenator wont charge...it could have a burnt fusible link in the harness at the starter or firewall,that will not let the current get to the gauge to indicate a charge if it IS in fact charging,and make you think the altenator is not working too...I'd put a voltmeter across the main output red wire on the back of the altenator and ground,and see if the voltage increases when you start it and raise the engine speed above idle...it should show 13.5 V at least if its charging..

 

[COKE]

Thanks diesel4me

It is an 88 ´Blazer 6.2 Diesel with the original engine and alternator(Delco Remy 12 Si 66 amps)
The first thing i did was to conect a voltmeter to the battery and check the voltage with the engine running,and it is the same as when it is off(11.56 or so) The dashboard voltmeter does work ok too.

The red wire has 12 volts all the time the other one does not have voltage,i suppouse because it shouldn,t to have.

Like i said before i have mounted a new regulator,diode trio,rectifier,brushes and it does not charge.
I,m considering to order a new alternator,but i want to be sure that the trouble is the alt itself and not other part of the charging system.

 

[diesel4me]

Both those wires on the small plug should have 12V with the key on or the engine running...if one dont,it wont charge,the regulator wont get the signal to turn on and start charging....you could use a test lamp or jumper wire to apply 12V to the "dead" wire and see if that makes it start charging with the engine running-(leave the voltmeter hooked up to the battery terminals so you can tell if it charges--usually you'll hear the engine slow down and the altenator make a whine if it starts charging).................................................-if it does charge with it jumped,then you have a break in that "dead" wire somewhere,or its not getting power from the ignition switch like it should be..if it still wont charge,there is probably problems internally in the altenator--some parts stores can test them on a bench tester here--not sure about where you are!..

 

[COKE]

Thanks diesel4me
Then that is ok.
The red wire has 12 v all the time and the other one has them when the ignition swicht is on.

I suppouse that the Standard motor products parts i mounted are junk.
It wouldn,t be the first time that i have troubles with this brand.

I,m considering to order a Powermaster 140 amps 12 si alternator,but i don,t know if it will be very much or something.

Thanks again

 

[diesel4me]

There is a "D" shaped hole on the back of the altenator case thats directly in line with a tab made into the regulator--by inserting a small screwdriver into the hole and touching that tab with it and grounding it to the case, it will bypass the regulator,and if you can get at it to do that (not possible on many engines because of the way its mounted or other things are in the way),you can see if it starts to charge with it bypassed (have a voltmeter hooked across the battery terminals while doing it,if you can access the hole )..if the voltage goes up when you ground that test tab,it means the regulator aint working...................................................................................................I used to sell Standard-Blue-Streak parts,most of them were very high quality--back in the 90's anyway...except for some cheap "Uni-Points",their quality was as good or better than most other brands were--of course you can get a defective part in any brand nowadays,with all the major brands farming things out to the lowest bidders......................................................If you upgrade to a higher amp altenator you'll need thicker wires to the battery also,or you risk frying the original wires...