I recently bought a 1970 Scout 800, like I need a project with an XJS sitting in the garage. I've had a couple Scouts in the past and like the Jags, there's just something about them.


The wiring on the Scout has been kinda butchered and I've got it pretty well sorted out. I want get this thing drive able before I start any major work.


My question is about my alternator, It's either new or rebuilt. It looks like a GM 3 wire, just guessing. I have a 250ma drain on my batt and I've traced it back to the alt. The drain goes away when I pull the plug off the alt. There is an external voltage regulator but it looks untouched.


I know there are internally and externally regulated alts, but, I don't know how to tell them apart. I'm thinking a volt meter might tell me, but not sure.


Any suggestions?

 

Terry, without knowing the exact alternator that we are talking about here, it is hard to say what you have. You mention that you have an external regulator, but then you follow it up with asking if the alternator is internally or externally regulated. I would hope that the person you bought the truck from knew not to mix an external regulator with an internally regulated alternator.

There should be some numbers on the alternator. Could you post those here. That would help me get you specific answers to what you are needing to know.

By chance, does it look something like:

This would be an internally regulated alternator.

Without putting my hands on the alternator, it is very challenging for me to give you the correct answer without more information.

 

Chris,


I couldn't get the pic to open. There is a tag on the alt with 7127-3, any help? On the back there is a lug marked Batt and a double connector, white and red. White goes to the batt lug and red goes to the ignition switch.


I guess my question mainly is, if it's wired wrong would that cause the small constant drain?


Also is there a test that will tell me if it's internally regulated?


I have seen on line how to hook up either scenario, but I'm not sure which I have.


Terry

 

Terry, the 7127-3 actually is what I was after. that tells me a lot about the alternator that you have. Just to answer the initial question, your alternator is internally regulated (ie, it will look at the battery voltage and control the field inside the alternator to maintain the 13.7 VDC output with the engine running.

If you look on the back of the alternator where you have the 2 wire plug on the top of the alternator, if you look on the case of the alternator, you should see the numbers "1" and "2" or possibly "R" and "F". Remember that 1 and R are the same post and 2 and F are the same post. The 2/F post should be powered directly off of the output of the alternator or from a wire coming from the battery post (better to get it off of the battery post as this is more representative of the voltage in the overall system). The 1/R post should be being powered by the wire coming from the ignition switch (ie, a source that is rated for atleast 10 amps and turns on and off when the ignition switch is turned on and off). if someone reversed these wires, it could lead to the discharge that you are seeing.

Hopefully this is helping you get things straightened out.

 

Chris,


Thanks for the help. Now that I know it's internally regulated I can proceed from there. I will make sure it's wired correctly and hopefully my drain will disappear.


Terry