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Thread: Lost all electrical power

  1. #1
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    Default Lost all electrical power

    Driving home last night and my car suddenly lost all power and blacked out at night. Not fun....... List of areas to look at?

    So far I have checked the fuses and insured the battery is solid and connected properly.

  2. #2
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    You checked the main 80 amp fuse?

  3. #3

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    Hi Oz here. I lost all electrical power to. I search the where the 80amp maxi fuse should be and nothing. No 80 amp fuse at all.
    I checked under the foot well and my top 40amp was blown. I put a fresh one in and wa la everything turned back on. I've owned my car since new about 10 years ago and have never had a problem like this.

    About 3 months ago my alternator went out. My tech put in a new one and every seemed ok. The battery which alarmed me to the problem was charging fine. Just lately it blew out again. Could it be that the new alternator is overcharging the system?

    Can any one give me some insight on this. When I went to change the fuse it felt pretty hot. Imagine driving at freeway speeds and everything goes dead. I'd hate to meet my maker over a $1.29 fuse. The emergency lights wouldn't even work. I'm not a born mechanic or electrical wizard, but I can follow directions if anyone can help I would appreciate it.

    Thanks,
    Ozm12

  4. #4
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    Sounds like a problem I had with my MGB. There is a saying - Lucas Electrics, Prince of Darkness. Perhaps the British heritage carries through stuff made in SA.

  5. #5
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    The real problem, as we discovered when recently troubleshooting a similar problem in my former car is that the factory used 10 gauge wire for the red power lead that runs from the alternator to a splice in the tunnel that then runs to the 80 amp fuse in the rear and to the 40 amp fuses in the front of the car. The 10 gauge wire is too small to handle the full amperage load in these cars and the result is that the red wire can, under full amperage load conditions, get hot enough internally to melt the insulation and often then back feeds power by fusing to the black and blue wires from the 3-wire alternator connector that run next to it inside the orange insulation sleeve a few inches from the alternator. Most owners have always assumed that this was being caused by heat from the front turbo, but that doesn't follow logic, since other wires that are in the same location and are totally exposed do not suffer any melting issues. This is also why lights flicker when driving the car at night. That 10 gauge red wire that runs the length of the tunnel to the front 40 amp fuses that feeds most of the electrical systems in the car is undersized. So when you are driving your cars in hot weather, with the A/C on, the radiator fans both running, the headlights on, and any other aftermarket system on, there is full amperage running through an undersized wire and that creates internal heat inside the wires, at butt connectors and at fuses.

    This doesn't exclude the possibility that you may have a short in this case that is beyond the 40 amp fuse that caused it to blow, but I believe that most of the electrical gremlins that have plagued these cars, is directly attributed to what I would consider a poorly designed electrical system that uses an undersized wire to feed the entire car from the alternator forward. This is what is causing the red wire to get hot enough to melt its insulation and fuse with other wires in the same loom near the alternator and to then back feed power that causes dash lights to stay on and a myriad of other crazy things, depending on which wires were fused to it. It is not front turbo heat melting these wires as everyone has assumed. The solution is to replace the red power lead from the alternator to the splice in the tunnel and then to the 40 amp fuses in the front and to the 80 amp fuse in the rear with at least 6 gauge red wire. Just my opinion, but something everyone should consider when discussing electrical issues in these cars.

  6. Default

    Quote Originally Posted by caccobra View Post
    The real problem,.... Just my opinion, but something everyone should consider when discussing electrical issues in these cars.
    What little research I have done, this makes sense!

    Would it make sense, did I mention that I have not done my research yet, to add a second parallel 10 AWG from the 80 Amp fuse to the front with its own fuse? Then you could break out either Relay C (build manual 8-11) or Relay D (build manual 8-11) and have the new circuit power it?

  7. #7
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    Quote Originally Posted by doug_porsche View Post
    What little research I have done, this makes sense!

    Would it make sense, did I mention that I have not done my research yet, to add a second parallel 10 AWG from the 80 Amp fuse to the front with its own fuse? Then you could break out either Relay C (build manual 8-11) or Relay D (build manual 8-11) and have the new circuit power it?
    It isn't enough to just replace the wire from the 80 amp fuse to the 40 amp fuse in the front. There are three legs that need to be addressed. 1. The wire from the alternator to the splice inside the transmission tunnel. 2. The wire from the 80 amp fuse to the splice inside the tunnel, and 3. The wire from the splice in the tunnel to the 40 amp fuse in the front of the car. The one that usually heats up enough to melt and then fuse with other wires nearby is the wire between the alternator and the splice in the tunnel. It usually melts a few inches away from the alternator and fuses with other wires that are next to it in that harness. Many owners have simply spliced in new sections of wire to replace just the melted section of wire by the alternator and then repair or replace the orange heat sleeve thinking it was turbo heat the caused the wires to melt together and that they have fixed the problem. They haven't really fixed the real problem. The 10 gauge wire is too small on all three legs of the power wire for the car. The only way to really fix it so it doesn't happen again is to replace all 3 sections with at least a 6 gauge wire IMO. I also think this red power wire should be run in a separate wire harness without any other wires in the harness with it, but that's just me thinking this would be the safest and best way to wire the car for peace of mind, if nothing else.

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    oh well, my to-do list was getting too short anyway.

    Thanks for the input.

  9. #9
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    I am currently going through this process. I had a question about the splice in the tunnel… where exactly is the splice? Is it near the back of the car, or is it somewhere in the middle? Just wondering if I need to take off all the underbelly pans. Also, is it just the 10ga power wire that has a splice? Or is it spliced to other cables as well?

  10. #10
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    I’ve had to do this fix on several cars - I haven’t had to remove any of the riveted underbelly pans, just the screwed-on pan under the engine, and the rear tunnel vent. Once those are off, remove the battery, and the top front heat shield that runs from in front of the downpipe to right below the front valve cover, and the silicone heat blanket that covers the ecu/relays, and you should have plenty of access to everything you need to get to.

    On at least one Noble, I replaced the main power distribution harness with one that I made from either 4 or 6 AWG wire - that went all the way from the alternator to the front fusebox, including the Y and the branch back to the 80 amp maxifuse. Interesting thing - once that was done, the headlights stopped flickering when the fans turned on…

    On another Noble, I measured the current draw at the 40 amp fuses at the front fusebox. With the headlights on and the fans going, if I remember correctly, the draw was somewhere between 39 and 45 amps, which would blow the 40 amp maxifuse. I haven’t confirmed it, but I think that there’s a possibility that, as the fans age, they start pulling more current, which pops the 40 amp maxifuse. Also, as these fuses age and heat cycle, they become brittle, which makes them more susceptible to vibration damage. I would suggest changing all the fuses (both normal and maxifuses, in both locations) every few years - use the old ones as spares, or for troubleshooting fuse blowing problems…

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