Alternator voltage drops to 10.4 with headlights on 88 cressida

[88sogreatv8]

So my 1uz swapped cressida has this weird issue. The voltage when either pressing on the brake pedal or turning on the headlights , drops the voltage down to 10.4 v when running . it stopped doing it then did it again.

I do have an aftermarket electric fan and a 1000 watt stereo system, so i thought," ok these alternators have 80 to 100 watts max output" . So i purchased a 150 amp alternator xat racing out of florida.

Just installed the new alternator with a jumper harness from a round plug to the oval plug , and after starting it up it stays constant at 14v now where it used to jump around between 13 and 14v , but still same voltage drop to 10.4v when the headlights are turned on.

SO.... couple things about this swap i did. the connector for the alternator is original to car i did not have to modify it whatsoever, it just plugged right in. secondly the voltage readings i am getting , are from a aftermarket usb outlet that reads voltage also. i wired it into the once existing cig lighter outlet in the dash.

What i am wondering is does this voltage drop stem from the way the voltage gauge is wired at the cig lighter? If you test under the hood at the battery directly it doesn't drop at all even with the headlights on. the only thing it seems to effect is when my subs are banging real loud and my headlights are on , the radio will shut off then come back on just to shut off again when the bass hits, like its not getting the enough voltage ??

Has anyone had any issues like this..Please let me know!! this forum has helped me solve so my riddles to my problems and im working all them out one kink at a time !!!!!!!!!!!

 

[numbchux]

Yea, your alternator Sense wire should be wired as close to the battery as possible to keep the voltage there correct. So it sounds like that's working as the voltage is correct at the battery. But if you've got voltage drop between there and your other circuits, you've got a bad connection somewhere. Could be right at the ignition switch, or main ground wire somewhere (engine to chassis, maybe?).

 

[Lextreme]

If you test under the hood at the battery directly it doesn't drop at all even with the headlights on.

Sounds like a non-issue then!

 

[ivan129]

So you if you have approx. 14V at the battery (this is what it should be if the alternator is charging) and you have 10.4V somewhere. Then its a real simple matter of:- Using a voltmeter, measure from the battery +ve post to negative where you get the 10.4V. If it measures 10.4V then you have a resistive negative feed. Do the opposite now. Measure from the batt neg to the +ve where the 10.4V and if it measures 10.4V, you have a resistive positive feed. Should be easy to trace from there.

 

[88sogreatv8]

So you if you have approx. 14V at the battery (this is what it should be if the alternator is charging) and you have 10.4V somewhere. Then its a real simple matter of:- Using a voltmeter, measure from the battery +ve post to negative where you get the 10.4V. If it measures 10.4V then you have a resistive negative feed. Do the opposite now. Measure from the batt neg to the +ve where the 10.4V and if it measures 10.4V, you have a resistive positive feed. Should be easy to trace from there.

Thank you so much for the advice , after preforming the test you recommended , i found that i wired the volt meters ground into the illumination wire , which apparently has a ground when the lights are off , but is energized with the lights on. found the correct ground wire and BAM its fixed . Thanks for the advice again .Once again Lexstreme forums to the rescue

 

[ivan129]

Glad to hear its sorted.