Charging Problems

[CSG]

I have an 87 4 cyl. coupe that I installed an 89 5.0 engine & wiring harness in. Problem is that The alternator does not seem to be working properly. The light in the dash does not come on, but if you disconnect the battery the car will die. Engine is grounded. Their is one ground to the apron off of the harness to the alternator. Changed the alternator, same problem. I haven't checked for current flow, but at the firewall solenoid I only see 12.4 volts while the car is running. Also all fusible links seem OK (voltage across).
Any help would be appreciated. Scott

 

[jerry beach]

Do not remove your batt. cable with the engine running. Are you running EFI? If so, you can cause voltage spikes that can damage your computer and sensors doing that. You should see 13.5-14.5v with the engine running. 12.4 is battery voltage only. Have the alt tested, its possible you got 2 bad ones. If its good, then you will have to re-wire or trace the problem in your harness. If it was me, I would rather look at a diagram and run some new wires, the factory stuff is too old to bother with.

 

[LXMiker]

buy a new alternator and see if that does anything

 

[rx7speed]

the 12.4 through the car while it is running is alt voltage as well jerry

but hey since you did a test at the batt you should have a pos wire off the alt
use that and hook the ground side of your voltmeter up to a ground

but you should have no more then a .5v drop from the reading at the alt vs the reading at the batt
if they are about the same and the below thing isn't that high you might be in for a ne alt

also if you can raise the idle up to about 2000rpms and see if there is any difference in voltage

 

[CSG]

Alternator is good. I need to know what every wire that connects to the alternator does & where it goes.

 

[89Notch]

the green one goes to the inside of the car, the yellow one merges with the black/orange one which is the charge wire, the yellow one tells the alternator how much charge to produce, and the white/black is the stator wire

to the best of my knowledge

 

[CSG]

I believe I have narrowed it down to the green wire to the dash and indicator. Does anyone know where this wire ties into a power circuit? From my research I have found that if this wire does not supply power to the voltage regulator to "excite" it that no voltage or current will be produced.