Charging Problems (1984 720)

[qletsinger]

 

So i just got an 84 720 and the charging system is a little messed up. The alternator was just replaced and brand new. The fusible links going to the battery seem to be in good shape. I did see the light in the dash with the batter symbol on it but i hasn't lit up ever since i have had the truck. Anyone have any ideas on what could be wrong? Some people are saying that the alternator might be a bad one. I tested the battery when the car was idling and it was in the very low 12's.

Thanks in advance!

 

 

[datzenmike]

If the alternator is charging you should have just over 14 volts across the battery when running, about 12 if not.

 

Key in ignition turn to on.... red battery symbol should light. Start truck light should go out.

 

 

 

 

Check that the two wire plastic plug is firmly seated into the back of the alternator. If you didn't change the alternator, check all wires are tight.

Clean battery posts and cables. The other end of the negative cable is important too. It's bolted to the intake manifold. be shur this is clean and secure. The positive cable goes to the starter lug. Check this also.

[qletsinger]

Yea that means the alternator is definitely not charging. The battery light doesnt turn on when i turn the ignition to on. Is there a chance the bulb is out? I will check out all those wires and see whats up! Thanks!

[datzenmike]

You know on some early systems the bulb has to be working in order for the alt to charge. If burned out you have no charge. One side of the bulb goes to the battery and the alt senses a charge from it to get going. I hate to say this is it, but pulling the dash and replacing the bulb is cheaper than replacing the alternator and it still does not work.

 

Anyone know about the bulb being blown??

[qletsinger]

Yea i was thinking that could be a problem. Before this i had a volkswagen and it had the same kind of deal with an alternator lamp. Can i pull just the gauge cluster to get back to the light?

[datzenmike]

Yes. You may have to reach up behind and unclip the speedometer cable if you can't thread enough slack in from the engine bay side.

 

First make sure wires on alt are clean and tight.

 

 

"https://www1.remyinc.com/webpictures/techtips/TT-557.pdf"]

 

1. Terminal L must receive voltage. This voltage is provided by the indicator
lamp on most vehicles. Failure to have voltage at terminal L may cause:

• No charge, Indicator lamp OFF.
• Charges OK, but indicator lamp is ON.
• Will not charge unless engine is “revved” up. Indicator lamp may come on
  when unit begins charging.

 

2. Terminal “S” must have battery voltage. This voltage is supplied directly from
the battery and will be present at all times. Failure to have voltage at this
terminal will cause:

 

 

• Overcharge or no charge condition, depending on alternator design.

 

3. The “BAT” terminal must have battery voltage. This voltage is supplied
directly from the battery and will be present whether the ignition switch is in
the “ON” or “OFF” position. Failure to have voltage at this terminal will cause:

 

 

• No charge, indicator lamp on.
• Extremely high voltage at “BAT” terminal.
• Possible damage to alternator diodes

[desert skipper]

About the same time you were having your no-charge issues I swapped out my old working alternator

for a new high-er Amp one. Fuses started popping to the electronic control box on my 81KC-4x4.

 

Voltage on digital cigerate lighteer moniter was 14.6 to 14.8 float, when running.

Out with the new in with the old. It now floats around 13.6 to 14.4....but fuses arent popping.

I had replaced the fuse with a circuit breaker. This saved a bucket of fuses, I'm shure.

 

This same fuse circuit included the electrical fuel pump. I "nascar wired" a single power

circuit for the fuel pump at the same time.

 

Are both alternators regulating voltage a little high.....?

[qletsinger]

Well actually i only have one and it isn't charging at all.. no fuses are burning out so i wouldn't think there is too much voltage.

[ryanw1]

I had same problem. It ended up being my voltage regulator. Had to hard wire a new set up using a relay. I belive its the blue wire with white stripe.

[qletsinger]

So these things have external regulators? Where are they located?

[datzenmike]

They don't have external regulators. The last external regulator was used in the '77 vehicles. All alternators now have a solid state (transistor) regulator built into them.

[ryanw1]

So these things have external regulators? Where are they located?

The regulator is in the alternator, but the wires that tell the regualor how much juice the battery has in it where not working. If you look at the back of the alternator there is a plug. Splice using a T fitting the blue wire with a white stripe then run the new wire to the postive termnal on the battery. Check your voltage it should be going up. If so then you need to run this wire to a relay. If you search online you can find how to wire a relay.

[qletsinger]

Ok i will have to try that! What kind of relay would i need?

[datzenmike]

The regulator is in the alternator, but the wires that tell the regualor how much juice the battery has in it where not working. If you look at the back of the alternator there is a plug. Splice using a T fitting the blue wire with a white stripe then run the new wire to the postive termnal on the battery. Check your voltage it should be going up. If so then you need to run this wire to a relay. If you search online you can find how to wire a relay.

 

While wiring a relay in may work, this isn't how Nissan does it. The properly working system does not need or use a relay.

[datsunaholic]

Change the bulb first.  That could be the whole problem.  All the relay and extra wires talk is working around an issue rather than fixing it.

 

You MIGHT be able to change the bulb without removing the cluster, but you'd need small hands.  Or a Wife/Girlfriend/Mother/etc who's not afraid to hunt under a dash, and doesn't mind a few scratches. 

[qletsinger]

Well i got up in there and the bulb was just fine! Does anyone have some good pictures of how the alternator is supposed to be wired?

[datzenmike]

There is a light color plastic  T shaped plug on the harness that fits into the alternator.

 

The top of the T has a white wire going to it that will have 12 volts on it because it is wired to the positive side of the battery. Check this with a meter. If no power the BLACK fusible link on the positive battery terminal may be burned out. *

 

The bottom of the T has a White/Blue stripe wire going to it that goes to the CHARGE lamp in the dash.

 

There will be a large BLACK wire on the case that grounds the alternator

There will be a Large WHITE wire to an insulated terminal on the case that goes to same Fusible link as above *

[qletsinger]

I replaced the alternator and it all works now! Thanks for all the advice!

[datsunaholic]

Replaced it again? Autozone or Oreilly "remanufactured" alternator? They have around a 50% DOA rate, at least in my experience.

[qletsinger]

Well the one that was in there was a remanufactured alternator that the past owner had bought new and it was bad. I got a new one at napa for 50 bucks and it works great!

[desert skipper]

Any comments on the voltage issue I posted earlier..?

I still question if my internal regulator is not too high.

 

I had swaped for a higher amp alt. Started popping fuses.etc

[datzenmike]

I suggest starting your own post so it's not confused with this one.

[Patthedog]

I recently ran into this exact situation with a ULTIMA remanufactured alternator. Something to mention the 2x4 and the 4x4 alternator look the same and will install the same but the output is different by 10 amps . I went thru the install fires mine up no battery light and my volt meter was at 12 . Started looking for possible answers and as the truck was running “ bout 3 minutes of screaming and ranting “ it suddenly started charging no clue why but felt the T plug that was mentioned previously and made sure it was good and snug 3 or 4 times am wondering if the terminals in the remanufactured alternators are slightly farther in causing a poor connection?