Troubleshooting Nissan Alternator

[Drscottsmith]

Anyone have a "test plan" for troubleshooting the Nissan Quest Alternator conversion?

I have everything installed with new harness from batt to alt and alt to starter, and new engine harness. New alt harness came with Nissan plug already installed for alternator and pigtail to B+ post installed, as well as two-pin connector to red and blue wires near firewall. Everything connected as far as a I can tell. Starter works.

No dash light for battery gauge, but gauge does read. No charging when the engine is running (gauge stays at the same level as ignition on). Voltage drops ever so slowly as engine runs.

Any ideas on best path forward?

[Tom]

Hmm... with all the new wiring, did you make sure to connect the exciter wire on the alternator?

[Drscottsmith]

Tom -

Thanks for the reply - that is the little single pigtail beside the Nissan Factory connector that connects to the main terminal with the heavy wire, correct?

That is how I have it right now. The eyelet connector on that little pigtail is on the big main terminal.

[Tom]

Tom -

Thanks for the reply - that is the little single pigtail beside the Nissan Factory connector that connects to the main terminal with the heavy wire, correct?

That is how I have it right now. The eyelet connector on that little pigtail is on the big main terminal.

See post #8 in this thread. In addition to the main post, there are two pigtail wires to connect, both in a little 2-blade connector socket on the alternator. The blade closest to the main power terminal (red in pic below) gets connected to that terminal. The other one (blue) needs to be connector to the exciter wire in the battery harness. If it already is connected, check that the little connector carrying that signal into the cabin is connected behind the power brake booster. If that checks out, make sure the cabin side of that connector has 12v when the key is in the on position. If it does not, check the battery warning light bulb in the dash to make sure it is not burned out.

alternator connections.jpg (119.23 KiB) Viewed 1133 times

[usury]

If it does not, check the battery warning light bulb in the dash to make sure it is not burned out.

The warning light is part of the exciter circuit itself, right? Is there an early vs late difference for this behavior?

I vaguely recall that having an LED in the warning light position poses a problem as well. May not apply to the original poster here, but for future reference.

[Tom]

If it does not, check the battery warning light bulb in the dash to make sure it is not burned out.

The warning light is part of the exciter circuit itself, right? Is there an early vs late difference for this behavior?

I vaguely recall that having an LED in the warning light position poses a problem as well. May not apply to the original poster here, but for future reference.

Yes, that's my recollection. The voltage regulator needs to be powered up via the exciter wire to work once the alternator is spinning. The exciter wire is down-stream of the bulb, which is wired in series. So it's like an old-fashion Christmas tree light string, where is one bulb goes out, the whole circuit is dead. Never heard the LED thing, but it makes sense. All LED's have a forward voltage drop, which I'm guessing throws off the voltage regulator. And for that matter, I have no idea what the path to ground looks like through the regulator, so that might pose a problem for the LED itself...

Not 100% sure about the early cars, but 'think' is essentially the same.

[Drscottsmith]

Ok -

So my connections on the alternator itself look like the picture above - but -

What is the little black plastic connector on the alternator? I do not have that. I will check continuity between the blue alt connector and the 2-pin near the brake booster (blue).

I did put leds in the dash, but purposely left the incandescent bulb in the battery light. The 928 works the same way - that light and a resistor are in series in that exciter circuit.

[four0four]

What is the little black plastic connector on the alternator? I do not have that.

I believe that's just a connector on the other end of the pigtail. Sounds like you got everything integrated into the harness, so there's no need for it.

Could you post some pictures? Maybe there's something that'll stand out. I just installed one of these a few months ago, and modified the (also new) harness to support it.

[Drscottsmith]

Here are a few pics:

IMG_0017.jpeg (181.48 KiB) Viewed 1080 times

Here is the plug in the back of the alternator. Heavy lead is on the top after I disconnected it. The yellow wire goes back into the harness to the connector in photo 3 below. The green wire has the eyelet I have on the main terminal post.

IMG_0018.jpeg (150.5 KiB) Viewed 1080 times

Another pic of connector unplugged.

IMG_0013.jpeg (163.63 KiB) Viewed 1080 times

Here is the connector by the brake booster. The blue wire is from the alternator exciter. The red wire goes to the starter.

I did check last night and have continuity from the plug to plug (Nissan connector to Booster-area connector). Now I need to check into the cabin and dash.

[four0four]

That about all matches up with what I've got on mine. Might be easier to just test at either the alternator or the connector up by the brake booster - look for power on the exciter line (relative to ground, not to the starter wire!). Apologies if that seems dumb, I'm not sure what else would be up...Maybe the alt's bad?