94 xjs is there something that turns off and on the alternator

94 xjs rebuilt the alternator and still have the same problem sometimes it charges 13.5at the batt. and sometimes 10 or 11 volts,if I remove the + cable when it running it stays running but at the same time, I check the voltage at the + end it only puts out 10 or 11 volts. Please help been working on this problem for the last 2 months. So if anyone has a clue I will be grateful

Never disconnect an alternator from the battery with the car running. That can destroy the diodes in the alternator.

Did you buy a rebuilt alternator? Lots of rebuilt electrical items are defective out of the box. If yours was rebuilt, take it back to whoever did it.

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Jon thank you for your comment but I have to say I have been working on vehicles now for about 50 years and I really pretty much know what I’m doing and I rebuilt the alternator and everything in it was replaced but the statter thank you anyway


Ther are two things that will disconnect your alternator.

First is overcharge relay. You can easily check it by turning the ignition off and on/starting your engine (with multimeter plugged in)

Second - is your drive belt. It simply surprises in alternator’s behaviour when loose. Usually slips on cold engine. Tighten it up!

And the old gits above are right, ‘amazing’ check with disconnecting the battery while engine runs is simply wan-ka-trouble-finding… Somehow, it seems that you’ve fried your diodes already - your engine should shut itself down righ after disconnection…

Thank you for your help can you tell me where the relay is and also thank you very much for your interest

Martin, out of my head, it was either above the fuses/under steering wheel, close to the A-post /or/ under the bonnet / top corner closest to the firewall/ on the fender. You’re having newer version with Ford making changes - so possibly it’s located under the fuel tank, or in a headlamp.

Check alternator belt first. Had the same, I’ve minced my banger upside-down just to find that nothing helps. It wasn’t charging on cold / during humid-rainy weater. The belt was tight but not tight enough as found out later, it wasn’t giving any squeaks or other sounds either.
Just give it a try.

If you have alternator on your bench, chfck the bridge diodes with multimeter, there is plenty of youtube guides how to do this, chdck each section. Your alternator needs battery to work - there is a tiny wire feeding the electricity into it. Worth checking. Have you also inspected ignition/alternator warning light’s lightbulb yet?
Just in case - if you’re having Bosch type - have a look here:

Thanks Jon I’ll give it a shot and see how it works out and I really appreciate your interest thank you very much. I’ll let you know how it works out

Joh I just wanted to let you know that my alternator is a denso and it has the main stud in the back for the battery cable hook to and the three wire round plug that plugs into the back. Thanks again man

there’s been a lot of comments about the pulley damper etc slipping… you could read other posts about that also

Thanks for your interest in my issue I have been out working on it and adjusting the alternator trying to get it to where it won’t slip also going to put some dielectric grease on the connections.

Hey John and everybody else that told me to check the belt I appreciate everything that y’all have done and all yours interest I went out and tighten the belt put some dielectric grease on the connections and lo and behold if I didn’t do it myself I would have swore that it wasn’t true but it worked charging just like it’s supposed to be thank you very much