Questionhi, i have a 1972 coupe de ville. the generator ligh comes on at ide.not all the time. most of the times.i've replaced the alternator,the belt and the battery. what else should i look at? also with the cables from the battery disconnected i get a resistance of 20 ohms between the 2 of them. is this normal? thank you. felix
Answerthe 20ohms, is that with the key out of the ignition, doors closed so the courtesy lights/door lights aren;t part of the circuit?
Dont have a manual so don't know what it's supposed to be.
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Check the resistance between the engine block and bodywork, negative battery lead, bodywork and engine etc.
Any resistances approaching 10 ohms should be investigated,
Undo the earthing leads clean contacts with emery till theyre really shiny, dab with grease and refit.
Also check where the wires go into the spade ends themselves, any corroded ends should be cut off and replced if there is enough spare cable (dont forget to allow extra for the engine shaking in its mounts)
Check the braided earth straps themselves too, if theyre green/white powder coated and starting to crumble, if they are looking a bit sorry for themselves replace them with modern equivalents, theyre very universal in this respect, just make sure they have the same type of faster (usually a stud bolt and hex nut, but as I said I don't have any specific information on this car)
Do all the earths (lights, wiper, accesories, radio...) if you have the inclination to do so to bring the efficiency of the old electrical system (in it's 5th decade WHOA!!) closer to original spec.
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and if it's not a simple wiring problem (given the battery, alternator and earths are known good...)
hmm 1970s... the sensor circuit that is resposible for bringing the charging light on is likely part of the instrument cluster.
but could be a module on the side of the alternator.
I think this may be over-sensitive and bringing the warning light on when there is actually plenty charge going to the battery.
if you could find the circuit diagram for the charging circuit/warning light circuit and find where and how the sensor circuit is plumbed in... once that is done you can figure out from there where problems might be arising.
Either that or find the circuit (by tracing the wires) that the warning light gets its feed from, maybe a part of that has become corroded or dirty (from getting wet/damp + 30 years of road dust)and is out of calibration due to this, something along those lines.
Either clean/repair or replace the sensor unit (whatever or wherever it is) or clean all the connectors/contacts etc along the whole length of the charging circuit/sensor loom -
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PS, you are getting 13+ volts at idle at the battery aren't you?
I'd expect 14.4V at idle or around that but anything over 13 is ok,
under that and you can get dim lights etc, in fact the lights are a good test - at idle and at night turn on all the accesories and lights, try to drain as much power from the battery as possible and keep an eye on the brightness of the lights, if after a while they dim or begin to pulse brighter and darker you are running the battery low and there actually is a problem with the charge level at idle, however if this does not happen the charging circuit sensor definately is over-sensitive and bringing the light on when no "insufficient charging rate" condition exists.
hope that helps ;-)
