10si one wire - Normal or bad?

[dennislbrooks]

As I was replacing a defective battery , + on first, when putting the neg terminal on battery last I get a spark --does not blow any fuses. Nothing is ON and key is off. When I disconnect the plus wire from the alternator -- no spark on neg reconect. Is this normal or is the alternator defective and I have a high resistance draw?

[VetteVet]

Originally Posted by dennislbrooks

As I was replacing a defective battery , + on first, when putting the neg terminal on battery last I get a spark --does not blow any fuses. Nothing is ON and key is off. When I disconnect the plus wire from the alternator -- no spark on neg reconect. Is this normal or is the alternator defective and I have a high resistance draw?

Unplug the large wire off the back of the alternator and if you have a multi-meter you can do a continuity test between the large post of the alternator and the alternator body. You should get near zero with the leads connected one way and near infinity with them reversed.

you can also connect the MM to the large wire and the alternator terminal with the MM on the 10 amps scale and read a draw from the battery through the MM into the alternator through the diodes and into the alternator body.
Anything more than .003 amps is too much and indicates that one or more of the diodes in the alternator is blown.

You can also connect everything and start the engine and take a voltage reading on the large terminal on the alternator to ground, and if you get less than 13.5 volts, you have a bad alternator, again most likely a blown diode.

You can also use a test light between the large terminal and the large wire of the alternator. If you get a light, you have a path to ground through the alternator diodes.

Another alternative is to just pull the alternator and take it to Autozone and let them test it for you.

If it fails and you want to replace it you should consider a later model 1-wire CS style. It's a bolt on and go and it does not have to have the engine revved to start charging.

I'm still a fan of the three-wire units and the CS 144 is one of the best for reliability, price and performance.

[gmachinz]

I agree with vette!

[dennislbrooks]

This is on the 46 chevy truck - still has the 216 but is now 12v. I will take my MM and testlight tomorrow to check for a draw per your instructions and if I have to replace will be getting a CS. I do run a voltage divorced regulator on the 67 --supposedly a solid state from JC whitney. Has been working fine since 2004 --charges 2 batteries --- one is an auxillary with a solenoid.

Probably should not have said anything about the 67. 8-)

At least in Ohio, Ford dealers have a sale ending 3-31-18. Did not matter if I wanted a delco or motorcraft ---- under floorboard in the 46 ---- but I got a 30 month 86 series Delco for $99.

Do you have a retailer/part number for a one wire 12si ---- same clocking as a 67 sbc --- with a good price?



thanks

[dennislbrooks]

All appears to be ok. Even tho it has a spark on battery hookup, it will not light a test lamp.

thanks

[VetteVet]

Originally Posted by dennislbrooks

All appears to be ok. Even tho it has a spark on battery hookup, it will not light a test lamp.

thanks

Did you get more than .003 amps with the MM connected between the battery cable and the battery negative post? With the alternator connected.

[dennislbrooks]

vetteVet/gmachinz --- it reads a steady 39mA on the 200mA scale between the neg post and cable with alt connected. It is enough to make a 2A maintainer go to yellow/green overnite before I disconnected. From my experience when a maintainer does abnormal things like a quick charge or maybe yellow/green at the same time --something may be wrong or suspiscious.


Please give diagnosis doctors. 8-)


I do have a new diode trio in the box and it reads about 135 Ohms each on the 200K scale with neg on the long tab to each of the short tabs, one at a time.