EndStar Posted June 12, 2016 Report Share Posted June 12, 2016 New battery and had alternator tested, all good. For some reason when the battery is plugged in I get 12.5 volts. But when I unplug the battery I get 15 volts from the alternator. Anyone have any idea what is causing this? Since it should be 15 when it's on. 78z with su carbs. Quote Link to comment
Lockleaf Posted June 12, 2016 Report Share Posted June 12, 2016 15 is too high. Anything above 14.5 Volts is considered too high. So you have a problem regardless. Is that at idle? Try running it up to 1500 or 2000 with the battery in and check it again. Quote Link to comment
EndStar Posted June 12, 2016 Author Report Share Posted June 12, 2016 15 is too high. Anything above 14.5 Volts is considered too high. So you have a problem regardless. Is that at idle? Try running it up to 1500 or 2000 with the battery in and check it again. Well its like 14.5 but I'm just rounding. And when driving it doesn't go up Quote Link to comment
MikeRL411 Posted June 12, 2016 Report Share Posted June 12, 2016 New battery and had alternator tested, all good. For some reason when the battery is plugged in I get 12.5 volts. But when I unplug the battery I get 15 volts from the alternator. Anyone have any idea what is causing this? Since it should be 15 when it's on. 78z with su carbs. IIt's called "no reference voltage"! If the battery was still in the circuit, you would get a reading that you could bother us with! The curent configuration voltage reading does not mean anything, 1 Quote Link to comment
EndStar Posted June 12, 2016 Author Report Share Posted June 12, 2016 I just woke up, so I'm but dazed and confused... in circuit it reads 12.2, not in circuit it reads 14.5 Quote Link to comment
banzai510(hainz) Posted June 12, 2016 Report Share Posted June 12, 2016 Maybe because it don't sense a battery it tries to overcharge. something is missing. a ground ref or something. sounds like alt is OK 14.1 would be best but if 15 for too long is going to cook your battery and ooze acid and ruin what pain there is in the engine bay. a 78 is a IR type alt so reg is inside. Quote Link to comment
I'm BLUE Posted June 12, 2016 Report Share Posted June 12, 2016 Are you looking at a multimeter or a very old stock gauge ? Are you testing this in hot weather ? (14.4 would be extremely optimal) Is it the correct alternator ? Are you testing off the alternator or battery or gauge ? (think bad or corroded wires depending). I have no idea if you converted to an IR alternator or not. If I recall correctly 78' was not an IR alternator year unless it was a 280zx.(unless I read your s30 year incorrectly). Fusible links wreak havoc in all of my s30 and s130's. So does the wiring in general. The battery being replaced may not have been required as a guess. Rounding up from 14.5 to 15 doesn't really help. Although you may just simply have a different problem then you thought to begin with. (Better or worse idk) Best luck and I'm not trying to be a dick. Quote Link to comment
EndStar Posted June 12, 2016 Author Report Share Posted June 12, 2016 Fixed it guys! And was checking with a multimeter from both battery and alt. Turns out stupid me forgot to ground out a toggle switch that gets power directly from a battery. Added a new toggle with a ground and it's back to 14.5! Appreciate the responses... man I feel stupid Quote Link to comment
That4doorKiD Posted June 29, 2016 Report Share Posted June 29, 2016 Can you give more detail about the toggle switch? I'm having problems with not charging Quote Link to comment
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