I really need your help, guys.
I have replaced my alternator twice in two days and still have the same symptoms: It starts out charging at nearly 14 volts. As soon as a load is applied (AC or radiator fan) the voltage at the battery quickly drops to around 12.3 volts.
I have cleaned ground connections, replaced terminals, replaced cables, repaired a broken ground braid under the cab.
My indicator lamp comes on when the key is switched on, but goes out after the engine is started. It did not even glow when the battery was dying out on the trail. Could this be a clue to my charging problems?

I don't know if this is directly related, but the engine is running like crap. I get code 23 Hard Idle Switch. What exactly is it and is there a way to test it?
(86.5 Z24i)
It is doing another strange thing: It will die if it is in gear when I lift my foot off of the clutch pedal. The only way it will stay running is if I keep my foot on the pedal just enough to push it away from the switch at the top.

Have you tested your battery?

ya, I would try putting the batt on a trickle charger( or better) and see if it want's to take a charge. how old is the batt?

Battery tested good, but I swapped in another known-good one, to be sure.
I ran a redundant 10 gage wire from the alt output to the battery and a new wire from the SENSE output to the battery.
Checked voltage drops on positive and negative cables and both are within .02 and .07 volt guidelines.
I think it has something to do with the LAMP circuit, but don't know where to start. I have been wrenching for two days straight and trying to get ready to head north for a week or so. I am probably too tired to think straight.

Did it just start after you did the efan swap?

do you have a tach and is it working?
are the ac and fan motors clean ?

from another post on another board a nissan trucker was having overcharging problems.
it turned out to be the alt.voltage regulator.
even though it checked out good several times..

good luck

quote:

Originally posted by danielmid:
Did it just start after you did the efan swap?

I would have to say "No" on that one. It started running poorly under load on Friday. I think that was caused by low voltage.
It ran great this morning to the end of the driveway. I could even take my foot off the clutch pedal without it stalling in first and second gear. After that, it still ran O.K. as long as I kept a toe on the clutch. Could be feed back though a circuit due to a broken ground somwhere, I suppose.
I'll be thinking about it all day at work. I would love to hear everyone's thoughts, no matter how odd they may seem.
Edit: I was reading a thread pertaining to the clutch switch. Nissannut seemed to know what they are for. I am trying to figure out how this applies to mine, but I keep thinking that I have to solve the charging problem first.

check all wire going to the alternator. one of them tells the alternator to charge. if that wire is busted or corroded would give you low voltage or a poor charging system.

quote:

Originally posted by Mountain Goat:
check all wire going to the alternator. one of them tells the alternator to charge. if that wire is busted or corroded would give you low voltage or a poor charging system.

I believe that is the "sense" wire. The sense wire checked good, but I ran a new one to be sure. I wonder if it has to be a certain gauge wire?
I also wonder if ther is a way to test the regulator or sense circuit to see why it doesn't work harder when the load increases.

quote:

Originally posted by tomas hayden:
do you have a tach and is it working?
are the ac and fan motors clean ?

Yes, yes and yes.

quote:

Originally posted by tomas hayden:
it turned out to be the alt.voltage regulator.
even though it checked out good several times.

How could I test that? I had VAutozone test this last one before I bought it. The previous one came from CarQuest the day before. Both new ones act like the one that came with the truck. I ran into this once on a van that I owned. The problem went away when I repaired a ground braid from the body to the transmission. Maybe I need to run more grounds?

try to diconnect the clutch switch .
then try it with a by pass.

a few years ago my fuel pumps power wires got damaged and sent an intermitent power surge to the frame of the truck .
the symptoms were strange and fleeting..

Make sure all 8 plugs are firing ALL the time at idle. Just unplug one wire coil wire at a time and start it up. Or pull the fuses. Theres a fuse for each four plugs.

quote:

Originally posted by nissannut:
Make sure all 8 plugs are firing ALL the time at idle. Just unplug one wire coil wire at a time and start it up. Or pull the fuses. Theres a fuse for each four plugs.

What would that show me? That one coil is not firing? Should I be able to tell a difference by listening?

It should sound the same on either 4 plugs. But its to test if one side is miss firing or not firing at all.

where are the two fuses that power the 2 coils located.??

quote:

Originally posted by tomas hayden:
where are the two fuses that power the 2 coils located.??

On the 720 they where in the dash fuse panel labeled "ignition". They where 10amp if I remember correctly. I used to pull them one at a time occasionally to test the two sides.

on the 86 d21 hardbody model ,where are the 2 fuses that power the two coils ,located?

quote:

Originally posted by tomas hayden:
on the 86 d21 hardbody model ,where are the 2 fuses that power the two coils ,located?

86 is still a 720. You must have a 86.5 early 87 model. Try the fuse box in the dash. I bet its the same.

I have an 88 truck/pathy FSM I can check if You dont see them.

Well, I hope its just a bad battery, but mine is dead at the moment. It was dead when I went out 3 days ago, and I thought it was just from sitting for 2 weeks. Jumped it, ran perfect, drove it around for an hour to charge up the battery. So I go out today to pull it in, and wham-o. Not even dim lights.

So I have it on the trickle, Im gonna leave it overnight. I was trying to figure out if I have any obvious drains, but I didnt find any. My CB is wired straight, so Ill throw a switch in there, and my other concern was the solenoid for the efan. Since it grounds through the solenoid, could it be draining out the battery all the time? Even when the fan isnt running? I dont see how this could really be possible, Im just trying to come up with a cheaper solution than a new battery.

I think Ill hit up my buddy who works at Wally World and use his discount to pick up a red top. Been meaning to do that anyways.

Any ideas on what I should check??? Im gonna take the battery in tomorrow and have it tested. I hope its that simple.