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Discussion Starter · #1 ·
While driving my '78 Spider tonight, I noticed that my generator light starts to come as as I hit 4000 rpm, then glows more brightly as I exceed 4000 rpm. Once I drop below 4000, the light goes out. (I never noticed the light coming on during the day though it's possible it's coming on then as well and I just haven't noticed. Otherwise I'm guessing running the lights at night is the difference). Should I assume an alternator issue, or is there another possibility? If alternator, can I just service it (worn brushes) or is the only fix to replace it? Thanks.
 

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How many volts at the battery do have at idle and say 3k RPM?
 

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Certainly the alternator can be serviced/rebuilt. That is the way I prefer. Find an auto electrical rebuilder - usually on the bad side of the tracks in the run down section of a medium size town. They will take your old unit apart, clean it, replace any worn parts and test it after assembly.

Is the drive belt properly tensioned? There should be ~1/2" deflection from thumb pressure along the longest span. Too tight wears out the bearings, too loose allows it to slip.
 

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There are rebuild instructions in one of the factory manuals that is on the Cardisc set. I agree with Eric - check the belt first. Otherwise could be brushes or a bad diode - both easy to replace.
 

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Discussion Starter · #7 ·
Belt seems to fine -- tension is about right and still plenty of grip on it. Interesting thing is that light only comes on at night after 4000 rpms, I guess because of the extra drain of the lights.
 

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I'd still suggest you get a baseline on the volts at the battery before you start tearing into things.
 

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first check is how many volts do you have across the battery at tick over, like tdskip asked?
If alternator is dodgy (or regulator for that matter) all sorts of gremlins will appear!
 

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You need to measure the current under full load to properly test the alternator. Poor brushes can give good voltage but not current. You could monitor the voltage then turn on everything - lights, heater blower, stereo, etc. and see if the voltage holds up.
 

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I have experienced that symptom a couple of times in the past, and on both occasions the alternator died shortly after. My guess is that a loop of wire on the armature has come loose, and under centrifugal force contacts the housing causing a short. Of course, it could be something else. But I'm guessing it's more than a loose belt.

Your car won't go up in flames or anything. But, I wouldn't plan any 500 mile trips across the desert before getting it fixed.
 

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alfajay..pftt.... where is the aventure in that.. crossing the desert, at night.. come on.. this is not a lucas car( would say british, but i have british car freinds)
 
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