another alternator thread...

[ymi5150?]

reaching out because i'm out of options

vehicle - 1968 C20 w/350 (no ac)

problem and data
car is reading below 12.6 volts when truck is running
car dies when positive battery lead is removed
white lead reads 0 vdc when key is on
blue reads 9 vdc when key is on


unsuccessful remedies so far:
new alternator
new voltage regulator
verified continuity between white and blue leads from regulator to alternator
new battery

my limited understanding is the white is the exciter and its odd to me that its reading 0 vdc but i dont know if it ramps to 12 vdc when the car is turning over. that should be regulated by the regulator.

bad alternator?

thoughts?

[ymi5150?]

more info.

the alternator tested bad at a big box store. replaced it, same outcome so i'm not sure if i have another bad one (doubt it).

i jerry rigged a jumper from the hot post of the alternator to the field terminal and it fixed the issue. the truck idles at 12.6 and revs up to about 13.1vdc.

i dont like the current fix but it tells me that the 9 vdc wasnt enough to excite the windings. i would think the battery would run down over time since its not switched power.

thoughts? is there an internally regulated, self exciting alternator i could upgrade to?

[dmjlambert]

I think it is very possible you could have another bad part from the parts store. I have seen weird symptoms caused by a bad battery. I don't know what the expected voltage reading is for the blue wire with key on. Somebody with more knowledge than me may need to chime in on that. A car parts store may be able to test all 3 parts involved, the battery, regulator, and alternator.

If you have some other problem not discovered yet and not related to those 3 parts, such as with wiring, then it probably won't fix it to upgrade. But if you are interested and want to proceed in that direction, it is probably a good idea anyway.

You can modify the wiring to accommodate an internally regulated alternator, or get an adapter plug that bypasses the external regulator. Then just bolt in a new alternator.

This article describes and gives application information about the later model alternators such as 12SI.
http://www.madelectrical.com/electri...elcoremy.shtml

And this forum thread has lots of info:
http://67-72chevytrucks.com/vboard/s....php?p=8254922
That thread also has information about upgrading to the CS type alternators which are even later model than the 12SI, and CS alternators require a different connector and a resistor to be installed in one of the wires or another adapter. Some of the CS alternators require the pully to be changed out because some don't have a v-belt type pully. O'Reilly Auto Parts changed the pully for me in the store on the CS144 alternator I bought from them to go in my 1969 CST/10.

[dmjlambert]

One more thing. If you have an instrument cluster with warning lights (as opposed to the more common instrument cluster with gauges), make sure your GEN warning light is not burned out. The GEN light should light up during starting, providing a built-in bulb test similar to the bulb test for the BRAKE light.

[VetteVet]

Originally Posted by dmjlambert

One more thing. If you have an instrument cluster with warning lights (as opposed to the more common instrument cluster with gauges), make sure your GEN warning light is not burned out. The GEN light should light up during starting, providing a built-in bulb test similar to the bulb test for the BRAKE light.

Small correction.
The GEN light will come on with the key on to ignition. It gets power from the key switch and grounds through the alternator diode trio. It stays on until the alternator begins charging and back feeds positive voltage back to the light to match the positive voltage from the key switch. The two positive voltages without any negative voltage will turn off the light.

The other light is the temperature warning light.

[Andy4639]

Originally Posted by ymi5150?

more info.

the alternator tested bad at a big box store. replaced it, same outcome so i'm not sure if i have another bad one (doubt it).

i jerry rigged a jumper from the hot post of the alternator to the field terminal and it fixed the issue. the truck idles at 12.6 and revs up to about 13.1vdc.

i dont like the current fix but it tells me that the 9 vdc wasnt enough to excite the windings. i would think the battery would run down over time since its not switched power.

thoughts? is there an internally regulated, self exciting alternator i could upgrade to?

13.1 volts with nothing on but the truck running? If this is correct then the alternator isn't going to keep up with charging when you start cutting on stuff. Crank the truck up at idle turn everything on you can and see what the reading is. Then rev the engine and see if it goes any higher.
My personal opinion is get the external regulator and toss it and get a internal. You'll thank me in the morning.

[Dead Parrot]

2nd the move to an internal regulated alt.

Simplest but not the best is to get what is called a '1 wire' alt. That is basically what you made with your batt to field wire fix. Get a 12SI model as it should be a physical drop in for your current alt. Some of the later CS models may require different brackets.

The 12SI has better cooling and a few extra amps output at idle vs the 10SI.

Best is an internal regulated alt conversion that preserves the sense wire to the junction block.

[VetteVet]

Originally Posted by ymi5150?

more info.

the alternator tested bad at a big box store. replaced it, same outcome so i'm not sure if i have another bad one (doubt it).

i jerry rigged a jumper from the hot post of the alternator to the field terminal and it fixed the issue. the truck idles at 12.6 and revs up to about 13.1vdc.

i dont like the current fix but it tells me that the 9 vdc wasnt enough to excite the windings. i would think the battery would run down over time since its not switched power.

thoughts? is there an internally regulated, self exciting alternator i could upgrade to?

Since you seem to know what wires do what, here's how easy it is to upgrade, this is not a self exciting alternator and you will need to have 12 volts on the exciter wire.








If you decide to keep the external regulator, you can trace the brown wire on the regulator ( it's the exciter wire from the key switch) back to the firewall and check it for 12 volts with the key on.

Here is the circuit for the exciter wire from the key switch to the regulator.






when I started my truck for the new cam break-in, I wired a key on hot source through a light and directly to the IR alternator I converted to,and it charged at 14.5 and the light went out as I described above.
It's basically what you did in your OP except that you need a resistance in the exciter wire (the light) or the engine may run on after key off. You also bypassed the external regulator so you can't leave it like that. If you ran the key on 12 volt wire with a light in it like I did, to the brown wire connection on the external regulator and you got the 13,5 volts at the alternator and at the battery then your regulator is working but it should be charging at 14.5 at 2K RPMs.

If you decide to get a three wire internally regulated alternator then here is a good way to wire it up. It eliminates the EVR altogether and you can use the brown wire from the firewall to the regulator,(provided you have 12 volts on it with the key on) and the red wire from the regulator and the main junction. Then you can eliminate the small blue and white wires to the old alternator.