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· Registered
6 Posts
Discussion Starter · #1 ·
Hey all,

I'm cold and stumped.

98 Frontier 4 cyl
Alternator wont charge the battery, here is the rundown so far.

Alternator is brand new but took it out anyway, bench tested good.
Battery is new (optima)
Checked positive cable from battery to alt - had continuity and low resistance
Checked grounds - okay
checked all fuses - main 80 amp good, Fuse 11 (10 amp) good, Fuse 36 (7.5 amp) good.
checked green/blk wire at the plug into the alt, checked out good (had battery voltage) (my understanding is this is the reference voltage of the battery for the alt)

After much reading I though I found the problem - my battery light was not illuminating on the dash with the key in the on position, I assumed my bulb was burnt out. Swapped in a good bulb still wont light up.

My understanding is the pin that serves the battery light in the back of the dash (which is yellow and black) should have battery voltage when the key is in the on position... it does not. However my oil light is still able to illuminate as well as my ABS light and I thought they were all served power by the yellow and black wire with the key in the on position, I must be mistaken.

Can someone verify for me that the yellow/black light should have battery voltage with the key in the on position? Or have other ideas of what the problem might be?
A through explanation of what exactly the yellow/black and green/black wires that hook to the alt. would also be appreciated.

My dash has been failing-OD shows all nines but my 100 ohm resistor next to the ABS light that would divert power to the battery light in the case of alt or battery failure is still good.

Any help or suggestions appreciated.


· Premium Member
8,577 Posts
Grounds - okay ...but not good?

My mower had a charging issue similar to yours...that was FINALLY diagnosed by a Mom/Pop Battery Shop "Tech" = bad ground cable = VOILA. The kid knew how to use a multimeter/etc...and solved a very frustrating matrix of confusion that had quite a few folks all scratching their heads.

· Registered
6 Posts
Discussion Starter · #7 · (Edited)
Wickedklown do you know where I could get a wiring diagram for the dash wiring?

I believe that power is served by the yellow/black wire and should be getting battery voltage with the key in the ON position. However I haven't been able to confirm this other than looking where the pins go and following the route that power flows on the dash.

I'm replacing my grounds today for good measure.

· Registered
26 Posts
I'm curious to what you find. I hope its its a simple thing, like a ground. I'm still surprised even today that one loose wire can send out symptoms to other things.

I can only think of one thing to suggest. Before this problem came about, was there any work done to your truck? Either by you or a shop? Long ago it was drilled in my mind to go back to the last thing worked on when gremlins appear.

Wires corrode, and wires can get fatigued when abused with out appearing that way. Good Luck.

· Premium Member
3,897 Posts
In my experience, most of the time the charging system warning light does not illuminate it is either the bulb has blown or the alternator is defective. That said, per the service manual regarding the charging light:

With the ignition system in the "on" position or "start" position, power is supplied:
-through 10A fuse #11 located in the fuse block (J/B)
-to combination terminal 29 for the charge warning lamp.
Ground is supplied to terminal 27 of the combination meter through terminal 3 of the generator. With power and ground supplied, the charge warning light will illuminate. When the generator is providing sufficient voltage with the engine running, the ground is opened and the charging warning light will not illuminate. If the charge warning light illuminates with the engine running, a fault is indicated.

So, after reading this and looking at the diagram, there should be a two pin plug at the alternator with two wires, a yellow/black and a green/black. If you unplug this connector, you should measure 12v (or battery voltage) at the yellow/black wire with the key in the "on" position. This would tell you that you are getting power from the 10A fuse through the warning lamp bulb and to the alternator. If you don't, you need to confirm power to the combination meter at pin 29 (white/black wire). If no power here with key "on," then check the fuse and circuit between the fuse and pin 29.
If you have power at pin 29, and no power at the yellow/black wire at the alternator (key "on"), then you need to make sure the charge warning bulb in the cluster is good and the circuit between the alternator (yellow/black) and pin 27 (yellow/black) at the back of the combination meter is good and not shorted/opened or have excessive resistance. If those all check out good and there is still no power to the alternator yellow/black, then there is an open inside the combination meter and the meter assembly needs to be sent out for repair or replaced.

The green/black wire should also have 12v, but at all times, receiving power from the battery through the 80A fusible link and through the 7.5A fuse #36 in the fuse/fusible link box near the battery in the engine compartment. If not, check the fuse, fusible link and circuit. You should also have 12v power from the 80A fusible link through the white 10g wire from the link to the "BAT" terminal on the back side of the alternator. This wire sometimes builds up corrosion within it and a lot of resistance, so make sure the wire is not burnt or excessive stiff. If it is, remove the fusible link and disconnect the wire from the alternator and perform a resistance check through it, which should be minimal.

Last, make sure there is a good ground at the black wire attached to the back of the alternator. If everything is good up to this point, then the charge warning light should illuminate with the key "on." If not, then I would suspect an open within the alternator and it needs to be repaired or replaced. Generally, I don't advise using aftermarket alternators due to my experience (and others) with their history of failures right out of the box or short service life. I prefer to stick with genuine Nissan remans or, at least, genuine Hitachi reman units. My gut feeling suspects a faulty combination meter in this case, but only doing the tests as described will confirm if that is the case.

· Registered
6 Posts
Discussion Starter · #11 ·
smj999smj Thanks for the concise write up! Once I got my hands on that FSM things got a lot more clear.

So here is where I am at currently.

I have battery voltage at the yellow black wire with the key in the on position at the alternator connector. I am able to make the charge indicator light illuminate by grounding this with the key on, both at the alt, and by grounding from the back of pin 27.

I have continuity from the yellow black wire at the connector to pin 27 (doubled checked just to be sure even though grounding at the alternator is the same thing).

Still no power at pin 27 but I do have battery voltage at pin 29 (white/blk) with the key on.

Okay so then I checked the green wire and did not get battery voltage there which should be constant... fuses are good... going to open up the fuse box soon here and check the white wire etc.

From my understanding though the green wire should not play a role in illuminating the charge indicator light correct? Meaning I have two issues? A bad combination meter and some sort of open or high resistance situation on the green/blk wire.

Is there more to a bad combination meter than the 100 ohm resistor and charge light? I checked the 100 ohm resistor with the light out of the circuit and it read fine (100 ohms)....
and if this is the case I would love to know who still repairs these dashes that you recommend. I emailed Mr. Whizzard two days ago and haven't received any reply yet.

Or am I misunderstanding the diagram and somehow the green/blk wire having constant battery voltage does play a role in illuminating the the charge indicator light? Either way I am still working on that issue but I want to get my dash sent out ASAP if the combination meter is bad.

Thanks so much for all your help so far! I forgot how much I miss forums.
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