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Hey guys, I have a shop working on my 97 and after installing the 3.5 engine they're now blowing the 120 amp fuse which I think is for the charging system. He says he tried isolating the fog lights, head lights , and window circuit but the fuse keeps blowing.
After he removed the black striped red wire ( see photo ) he claims the cars runs with out it connected. I told him I'm pretty sure it's the charge system wire but he doesn't think so since allegedly the car runs without the wire. I told him that's cause you're running on the battery only. He's claims he checked and had 14.2 volts on the charge circuit. Any ideas what could be causing the fuse to blow? I never had any electrical issues with this car and I've owned it since 97 brand new.
The 120 amp fuse is the so-called "gate keeper" to isolate the high current draw devices from the battery. There is only one device that connects to the fuse directly and that is the alternator. Everything else connects to this fuse through another, lower amperage fuse, 30 amps or less. So if any of these other devices were to short, they would blow their own fuse first.
I'm not sure what that red/black strip wire connects to, but in general there is probably a smashed wire that is not being detected.
Looking at the diagrams and following the wire labeled B/R it looks like that wire I'm holding in the picture above is the same wire in the diagrams going to the alternator.
Has to be a shorted wire in that circuit somewhere. They should be able to figure it out now that they can follow what circuits are connected to that wire.
Last edited by maxprivate; 03-17-2017 at 07:13 PM.
Yeah, that black/red stripe wire goes to the alternator. I would disconnect the wire from the alternator and do a continuity check on the wire to ground. But if they are truly measuring 14.2 volts on the alternator, then the wire can't be shorted.
However as a sanity check, I would measure the voltage at the alternator terminal with the engine shut off. It should measure 12 volts (battery voltage) if the fuse is not blown. If the fuse is blown, the voltage reading would be 0.
Yeah, that black/red stripe wire goes to the alternator. I would disconnect the wire from the alternator and do a continuity check on the wire to ground. But if they are truly measuring 14.2 volts on the alternator, then the wire can't be shorted.
However as a sanity check, I would measure the voltage at the alternator terminal with the engine shut off. It should measure 12 volts (battery voltage) if the fuse is not blown. If the fuse is blown, the voltage reading would be 0.
I didn't witness what they checked and where they measured 14.2 Volts from but the diagrams show the Black/red wire in my hand is the charging circuit so I don't get how he claims the car charges with the wire disconnected. I think he was just talking to buy time to figure it out.
True about checking that B/R wire to ground from the alternator. I'll post more info this coming week when they get back on the car to further diagnose.
This was happening to my brother and we were killing ourselves trying to figure it out.
The black plastic isolator piece on the alternator that sits under the power wire had broken (probably overtightened when he changed his alternator) which kept causing that fuse to pop.
This was happening to my brother and we were killing ourselves trying to figure it out.
The black plastic isolator piece on the alternator that sits under the power wire had broken (probably overtightened when he changed his alternator) which kept causing that fuse to pop.
Did you have to replace the alternator to fix the problem?
funny, I know a guy who worked at Nissan more the 25 years, He said that the alternator plastic piece is a common problem.
He fixed the problem. Said it was a black wire grounding out on the chassis when the motor flexed. Didn't tell me exactly what wire but it had to be one in line with that 120amp fuse.
Good to hear that they found the problem and you can get back to driving the car!
It would be of curiosity value to know which wire was the problem. In the color coding Nissan uses, black wires are ground and color wires are hot. If the wire color is solid, it is connected directly to ground (black) or to 12 volts (color). If there is something between the direct connection such as a fuse, switch or device, then the wire will have a stripe on it.
Good to hear that they found the problem and you can get back to driving the car!
It would be of curiosity value to know which wire was the problem. In the color coding Nissan uses, black wires are ground and color wires are hot. If the wire color is solid, it is connected directly to ground (black) or to 12 volts (color). If there is something between the direct connection such as a fuse, switch or device, then the wire will have a stripe on it.
Yea I'm definitely going to find out which one it was and post back when I do.
This was happening to my brother and we were killing ourselves trying to figure it out.
The black plastic isolator piece on the alternator that sits under the power wire had broken (probably overtightened when he changed his alternator) which kept causing that fuse to pop.
Chris, that was the same exact problem with mine.. The rubber boot was torn causing the wire to touch metal.
03-16-2017, 10:26 PM
