Hi,

the main 140A fuse on the + terminal blows when I connect the brown connector with red and white cables to the fuse link (also connected to the + terminal). See attached pic.

Is anyone able to tell me to what these cables are connected ?

Thanks in advance

It would help to know the year of your ride, but the Red one generally goes to the Fuse & Fusible Link Box. The White one generally splits to the IPDM and the Ignition Relay. Since it should be blowing the 100A B or 80A C sub-links in the card and not the main 140A A link, I think your short has to be something that's trying to switch on when you give it power. The Ignition Relay is the only unfused connection I see in the WD's which originates through those links.

Thanks for your reply.
The year of the Z is 2009.
Well if I understand correctly that could be a short with the starter or the harness connected to it ?
Sorry if I misunderstood, I'm pretty new in the 370z world of troubleshooting.
I was suspecting the starter and plan to remove it, to test if the short is still there or not.

Could you indicate me where the ignition relay is ? That could be a quicker way to check that.

The starter is unfused on a 370, that 140A link is for the alternator. You can see the layout here on page PG-6, the links to the brown connector (E1) are B and C:
https://www.nicoclub.com/service-manual ... 9%2FPG.pdf

You can see that if the alternator main circuit was shorted, it would be blowing the 140A link regardless of whether E1 was plugged in or not. What's curious is, if the short is in anything downstream from E1, it should be blowing the lower-rated sub-links B or C and not the 140A link. The fact that link A is blowing means the short has to be "secondhand", it's the result of something switching on only when B or C are powered up. The only thing I can come up with is a melted regulator in the alternator which is causing a ground short when it tries to power up. For that reason, the first thing you should try is disconnecting the alternator cable lug from the battery card. If the short disappears with the alternator lead disconnected, you can be pretty certain the alternator is blown.

Those link cards are expensive, so to troubleshoot this I'd suggest you pick up a 150A thermal breaker and wire it across the blown link, that will allow you to mess with the power without blowing up more hardware. They sell 12V resettable breakers up to 300A for car stereos, your local parts store probably has some. Here's an example of a 150A:
https://www.ebay.com/itm/284398493852

Big thanks Vstar
I was struggling finding this electric diagram, and to be honest I was struggling understanding these kind of diagram.

First, how do you know that the brown connector is E1 ?

The only part I don't really understand is "The fact that link A is blowing means the short has to be "secondhand", it's the result of something switching on only when B or C are powered up."
It seems that B and C are "after" the 140A fuse, and B or C are not connected to the alternator which seems to be the culprit according to the diagram, as you mention after. Or maybe I missed / didn't understand something (I'm french, english is not my mother tongue).

Anyway, thanks again for taking the time to answer me.

I'll try to explain better. Since E1 is "downstream" from the connection to the alternator, if the alternator main circuit (stator, rotor or brushes) was causing the short, then the 140A should blow regardless of whether E1 is connected or not. Since it only blows when E1 is connected, the short must be occurring only when something powered by E1 is switched on. There are various things inside the alternator that could fall apart and cause a short through the field ground circuit of the regulator, such that it would happen only when the regulator attempted to power-up. If you look at CHG-15 here...
https://www.nicoclub.com/service-manual ... %2FCHG.pdf
...you'll see that the field terminal for the alternator (which also supplies logic power to the regulator) is powered through fusible link B on E1 by way of fuse# 32. So the regulator will only power up when link B is connected. The simplest way to prove that the alternator is blowing the link is to take the alternator main wire loose at the battery (terminal 6 in the diagram, but it's just a big ring lug). That's because that fat wire doesn't go anyplace else, it goes straight from the 140A link to the alternator output terminal and noplace else. So if it quits blowing the 140A link with that wire disconnected, the problem is definitely in the alternator. If it doesn't quit blowing, then frankly you have a mystery problem I've never seen before.

If you go back to the PG section and look on PG-9, you'll see pinouts and wire colors for all the connectors in the preceding diagram. Most Nissan WD's after about 2006 use that format, with the pinouts and colors on separate pages following the diagram. The alternator lug is E203 and shown on PG-12, it will be a fat BLK/GRN wire. The starter connection E204 will be a fat BLK/YEL, so you can easily make sure you're disconnecting the right one.

I have found the issue. Wait for it... That's the mystery thing you wouldn't suspect.
But in respect to the long extensive answer you wrote I've read and understood the logic. Thanks for taking that time and your patience for explaining those rather abstract diagrams to me. Much appreciated. I wish there would be more helpful people like you on FB / in the forums.

So now, I was about to pull the car out of the garage with a forklift truck, then push it on a lift (not sure of the word). The plan was to test the alternator by disconnecting the + wire on it. But as you mention there would be another way.
I was already imagining myself struggling removing the thing and replacing it. I've looked the prices and some how to videos yesterday and it didn't look as simple as I expected (I'm used to work on Z32).

But just before, I have heard that sometimes shorts can happen inside the battery... So you now what happens next. I test with another battery, no short, the car starts like a charm.

I would not have bet one dollar on that damn battery because it seemed ok, powering interior lights and the parking lights when connected to the terminals. The issue only happened when the brown wire was connected so you would logically suspect something down that line. Like you and I did.

Anyway, that's the first time I see that. So does my father. I'm glad to avoid a possible big bill at the dealership and simply have the possiblity to run again that car I was about to hate. But at the same time this is infuriating to have spent so much time on this and finding finally that's a so simple thing (I did a lot of tests before finding the brown wire, including a lot of harness parts, fuses and relays as I haven't the electric diagram).

Anyway, thanks again for your help

That's a new one indeed. Glad you got it straightened away, happy motoring!

BTW, yes, "lift" is the correct English term.

Hey... I'm back with 2 new issues.

First : check engine light on. I guess I will have to buy a code reader. The car is seems to run normally.

Second : no sound at start. I checked fuses and the "Bose amp" one was fried. Sound came back everywhere except for the subwoofer. I tested voltage between the black and yellow cables of the plug (they are bigger than the others) and I get 0 volt. Is there a dedicated amp for the woofer ?
I checked the fuses in the 3 boxes, nothing seems corresponding.

The woofer has its own amp and a separate 15A fuse, #5 in the cabin fuse block. You can get your audio WD's here and the power layout in the PG section I linked earlier.
https://www.nicoclub.com/service-manual ... 9%2FAV.pdf

I think I know the fuse you're talking on. It was called audio and I checked it, was ok.
Page 38 of the AV part of FSM there is only one Bose Amp feeding speakers and the subwoofer.

Or am I missing something?

The woofer has an amp built-in, sorry if that wasn't clear. One of the three data wires into the woofer assembly is an on-off signal for it.

Ok, got it.
So if there is no signal, there is no power. That could be the problem.
Or the signal could be OK, but the power not.
If I understood correctly, the signal comes from the main amp. So there is a voltage on the signal cable. I found which one on the plug is the signal in the AV section. What I don't know is if I can test it disconnected or if it's mandatory as there is a kind of loop with another signal from the woofer to the Bose amp.

For the power test then.
Is my testing method correct ? I turn on the head unit, then I test the voltage between the yellow and black wires. I suppose I should get something else than zero if the signal is correct.
I've looked in the entire PG section, found nothing relevant for this issue. There is a 20A fuse for the Bose amp, which I changed to get back sound to the speakers.
There is also a 15A fuse for the woofer. I thought it was the one named "audio" in the cabin fuse box but I'm not sure anymore.

Use the link to the PG section and go to PG-84 through PG-86, it gives you the numbering for all the fuses and fusible links in the car. The on-off signal only turns the woofer on and off. The woofer won't function without it, but it doesn't interrupt power to it. The fat Yellow wire should have power even with the car off. Since the Bose fuse was blown, I'm kind of wondering if maybe you have a problem in the Body Harness. The wire-to-wire connectors M25:B2 which carry power for the Woofer are under or above the lefthand kick panel, see PG-73 for the harness layout.

I'm probably too dumb for that
I looked at the fuse part, there are numbered, great. That doesn't say their function. The problem is that you have to research the whole document to see what they are for. And unfortunately the research function doesn't work on diagrams... So this is more practical to look directly on the covers in the car.

I've checked the signal cable : it shows 12v.
The problem is that here is no current to the main yellow cable which should be powered all the time. I couldn't find any fuse for that, which is weird.

I've looked in the PG 73 section. This will be tricky to find the issue in the body harness if this is the cause.
And by the way, what are all the B# stuff on the diagram ?

You need to correlate the fuse number shown in the wiring diagram in the AV section to the fusebox drawings in the PG section, that will get you to the right fuse. In this case it should be #5 in the cabin fusebox. If there's a problem in the harness it may be difficult to track down, but the first thing I'd check is the M25:B2 connection under the lefthand kick panel. Connectors in that area often get wet and corrode, causing all sorts of strange problems.

Thanks for the precision regarding the fuses.
I'll check the connection but I honestly doubt that it could be the cause.

Additionally, I made a "bridge" between the 12v signal cable and the yellow power supply cable. I simply pushed a cable between the 2 cable at the back of the wire. Then I checked and had 12v on both (that was the goal). But the woofer remained silent
Does that mean that I have also an issue with the woofer amp ?

Probably, but It's possible that the output on the Bose is blown. You can check that with your voltmeter on AC. With the woofer disconnected, the system on and sound at the other speakers, put the meter across the Sky Blue and Violet wires. You should see an AC voltage that increases as you increase the volume. If not, the Bose output for the woofer is blown. If there is voltage, then something inside the woofer is blown.

Ok, that's clear. I'll run the test on Saturday. The car is not at my home and I will probably get back to it Saturday.
Worst case, I buy a new amp and woofer.

Could you confirm that with the bridge I put between the signal cable and the power supply one it is supposed to work ? I wonder if I could let this as it is.

Provided it also has ground, yes. When checking you should measure from the ground wires in the amp and woofer connectors and not from a chassis ground. That way you verify both good power and good ground. If ground is good and a jump to power doesn't wake it up, then something is blown, the Bose, the woofer or both.

I guess ground was good. I measured between the bridged yellow and the black ground just below. That showed 12v.
But I didn't check directly at the Bose amp and woofer amp. I need a big torx to remove the woofer as I guess the amp is below.

I looked at the prices on ebay for both, I was expecting these way more expensive. I let you know what I find next Saturday.

My bet is the Bose amp is partially fried despite the fuse has blown to supposedly protect the amp...

Kramours wrote: ↑

Tue Sep 13, 2022 3:50 pm

My bet is the Bose amp is partially fried despite the fuse has blown to supposedly protect the amp...

That would be my guess also. Sometimes fuses "just fail", but not often. Usually there's an underlying reason.

Hey.
I've done some tests.
First I ran a cable between the battery and woofer power supply because I wasn't sure of my bridge thing : didn't work.
Then I checked the violet and sky blue cables which go to the speakers : they show voltage. Confirmed with an old speaker I plugged to them.
I also opened the woofer. I plugged the 2 speakers to the amp I have in another car : they are fine.

Conclusion : the amp in the woofer box is fried.

Sounds like a right diagnosis.

I've just ordered a complete woofer (no one sells only the amp). It comes from Lituania, I will have to be patient.
Thinking of it again, that sounds logic. No fuse between the battery and the woofer's amp power supply wire (this is weird btw). So the short directly fried the amp. Hopefully the big amp was protected by the fuse that blown.

I received the new subwoofer. Unfortunately it doesn't work. What I tested :
- check signal to the woofer : 12v, ok
- link the + battery terminal to the yellow + cable : doesn't work
- bridged the + wire and signal wire to have 12v on both : doesn't work.
- bridged the 2 ground wires : doesn't work
- bridged both the 2 ground wires and the signal and + wire : doesn't work.
- tested the R and L signals after the Bose amp : it works.

I'm lost. It goes beyond what I could understand.
I'm considering to sell this car as it's slow (I'm used to modified 300zx) and globally a pain in the a** so far. Additionnally it's subject to the oil gasket failure that I really don't want to experiment.

Anyway I would like to fix that before selling this for the next owner.

If you're sure there's audio signal on pins 1~2 (SB, V) then the woofer isn't rocket science, it needs power, ground and an "on" signal. Y to B should light a test lamp, if so then power and ground are good. GRay might be active low (the FSM isn't clear about that), but it should change when you switch the radio on and off at the dash. If not, then the "on" signal isn't getting there.

The only thing not working for unknown reason is the yellow 12v battery supply. But I connected a long cable between the + battery terminal and the yellow wire. It didn't work better.
Everything else is ok. Signal shows 12v when radio is on, speakers signals to the sub amp are ok (tested with a spare speaker). Grounds are ok. I've already "made" numerous sub and amp stuffs, with sometimes several amps. This situation doesn't make any sens to me.
I'm pretty sure that if I connect the sub in place of my amp in my daily it will work.
It would require to cut cables though....

Have you checked Y to a chassis ground instead of B? If you have a bad ground on B, you'll read 0V between Y and B even if Y has power. The woofer needs both in order to work, having no ground is the same as having no 12V.