Dead car

[lowman240z]

I am currently restoring/refurbishing a 1973 240z.I bought the car after the engine/trans and clutch had been rebuilt.On the way home after purchase the alternator went bad.It had been changed to use a 280z alternator with the built in voltage regulator.I replaced this and the battery and everything was good for 2 brief drives and multiple start-ups.On the 3rd drive something started smoking and the ammeter was pinned to the right tach stopped working.I was amile from home.The car drove fine.After I shut it off and the smoke stopped I found that it was coming from the speedo cable and that a ground wire from the battery ground cable to the firewall had burned in half.I also found that the area where this wire made contactwith the firewall had fresh touch up paint under it.I removed the paint,bought a new wire and installed it with good connection on both sides.The battery is fully charged,but when I turn the key nothing happens.No noise,clicking etc.When the car was out of commision before I replaced the wire I did have to change the indicator switch,but all of these connections look good.Does anyone have any ideas where to go from here?

[grantf]

Wow all I can say right now is check fuses and fusible links. sorry the most obvious

[SteveJ]

PM sent.

[SteveJ]

I am currently restoring/refurbishing a 1973 240z.I bought the car after the engine/trans and clutch had been rebuilt.On the way home after purchase the alternator went bad.It had been changed to use a 280z alternator with the built in voltage regulator.I replaced this and the battery and everything was good for 2 brief drives and multiple start-ups.On the 3rd drive something started smoking and the ammeter was pinned to the right tach stopped working.I was amile from home.The car drove fine.After I shut it off and the smoke stopped I found that it was coming from the speedo cable and that a ground wire from the battery ground cable to the firewall had burned in half.I also found that the area where this wire made contactwith the firewall had fresh touch up paint under it.I removed the paint,bought a new wire and installed it with good connection on both sides.The battery is fully charged,but when I turn the key nothing happens.No noise,clicking etc.When the car was out of commision before I replaced the wire I did have to change the indicator switch,but all of these connections look good.Does anyone have any ideas where to go from here?

I went to see if I could help Scott with his car. The car looks to be in pretty good shape. It spent a significant portion of its life in California, possibly in Northern California. The car does not look like it had been abused. The alternator had been swapped to an internally regulated alternator, and the car had the plug with the proper jumpers in the socket for the voltage regulator.

He had disconnected the battery before I arrived, but it had been connected for a while. The battery voltage was 1.4 volts and dropped to zero when I connected the battery cables. I took the battery cables back off and checked the resistance from the positive cable to the negative cable. It was less than 1 ohm. We disconnected the alternator but discovered that the ring lug for the ground had broken when he replaced the alternator previously. (We put a new ring lung on later.) The resistance was still below 1 ohm. We unplugged the jumpers for the voltage regulator circuit with no change in resistance.

I unplugged all of the fuses in the fuse box. The fuse box showed signs of corrosion. The lid showed melting that was not reflected by the fuse box, indicating that the fuse box had been changed out previously. With all of the fuses removed, the battery terminals finally showed an open circuit. We started replacing the fuses one-by-one. When we plugged in the fuse for the parking light/brake light circuit, resistance dropped dramatically. I disconnected the ground from the combo switch. No change. I put the ground back and pulled the connector going into the wiring harness. No change. I reconnected the wires to the combo switch. I inspected the brake switch for proper operation, and it worked. We pulled all of the side marker lights, tail lights and front turn signal lights. I found some corrosion in the lights, but I don't recall seeing any corrosion completing the circuit.

Things I did not check:

1. I did not look for the installation of an aftermarket alarm.

2. I did not look to see how the stereo was wired in.

3. I did not inspect the back of the fuse box.

Does anybody see anything that I missed (besides the back of the fuse box)? I believe Scott may be intending to order a modernized fuse box from MSA. Anyway, I'm open to suggestions.

Steve

[Zs-ondabrain]

On a more thorough aproach, I would physically unplug each side marker, one at a time. Just like you did with the fusebox (good move by the way) and test with each unplug. Then check the front markers as well. Then the taillights.

If you did the whole underdash test as stated above, then hopefully, it's one of the untested lights in the same circuit.

Also, People usually buy an aftermarket fusebox because of the headlight or parking light fuse melting the typical area's. My upgrades usually solve that issue, and with the $200 price tag, you could purchase both of my uprades, and from the same website. MSA.

Dave

[SteveJ]

On a more thorough aproach, I would physically unplug each side marker, one at a time. Just like you did with the fusebox (good move by the way) and test with each unplug. Then check the front markers as well. Then the taillights.

If you did the whole underdash test as stated above, then hopefully, it's one of the untested lights in the same circuit.

Also, People usually buy an aftermarket fusebox because of the headlight or parking light fuse melting the typical area's. My upgrades usually solve that issue, and with the $200 price tag, you could purchase both of my uprades, and from the same website. MSA.

Dave

Dave,

I was hoping you'd chime in.

I already suggested to Scott that he contact you about the headlight relay upgrade. The parking light relay upgrade might not be a bad idea, either. (Scott is probably going to think I'm on your payroll;)) The fuse box that was in the car showed plenty of signs of corrosion. That's why I suggested the fuse box upgrade.

We tested with all of the tail lights, turn signal lights, and side markers out, and the circuit was still shorted out. I'm not sure just testing with just one bulb out at a time will make any difference. I didn't test from the harness connection under the dash (Green wire with Blue stripe) to ground. That would have confirmed whether or not the short was between the fuse box and the combo switch.

Another thing I didn't check was to see if the inspection lamp was on. I tested that theory with my own car. I did see a significant drop in resistance, but it wouldn't account for readings as low as what I saw on Scott's car.

Anyway, it will be another week or two before I can help Scott again, so maybe I can develop a test plan to ferret out the offending circuit by then.

Steve

[geezer]

Just thinking out loud:

-Check for an electrical system by-pass into another circuit. A common problem caused for a variety of reasons. Corroded, wet, mishaped light sockets, or weak, damaged springs. Those are the easiest to find but a by-pass can be caused by chaffed wires, or burned insulation or a number of other causes, anywhere in the circuit. I usually leave the battery terminals disconnected and then supply power to the questionable circuit, then check the other circuits for a by-pass.

-Bad grounds can cause some pretty funky things to happen also, that have left me scratching my head.

You guys are probably much more familiar with the Zs circuitry than me. I'm just dreaming up scenerios. I used to go to sleep at night with an electrical mystery on my mind and wake up in the morning with a fresh idea that solved the problem.

PS - It is helpful to have a helping hand to activate switches while checking for a by-pass. It is a process of elimination. I doubt I told you anything you don't already know or won't think of after sleeping on it.

[SteveJ]

Just thinking out loud:

-Check for an electrical system by-pass into another circuit. A common problem caused for a variety of reasons. Corroded, wet, mishaped light sockets, or weak, damaged springs. Those are the easiest to find but a by-pass can be caused by chaffed wires, or burned insulation or a number of other causes, anywhere in the circuit. I usually leave the battery terminals disconnected and then supply power to the questionable circuit, then check the other circuits for a by-pass.

-Bad grounds can cause some pretty funky things to happen also, that have left me scratching my head.

You guys are probably much more familiar with the Zs circuitry than me. I'm just dreaming up scenerios. I used to go to sleep at night with an electrical mystery on my mind and wake up in the morning with a fresh idea that solved the problem.

PS - It is helpful to have a helping hand to activate switches while checking for a by-pass. It is a process of elimination. I doubt I told you anything you don't already know or won't think of after sleeping on it.

Ron,

I opened the floor for brainstorming. It doesn't matter if you tell me something I already thought of. I'd rather have that happen than for an idea to be left out. Anyway, I inspected some of the wiring around the combo switch when I was looking at the car, and I did see some signs of overheating. I did not observe any insulation that had burned through or any solder joints that looked overheated.

Steve

[Zs-ondabrain]

I think your by-pass theory is kinda what I was trying to get at, when I mentioned "physically disconnecting each light" but yes, every little bit helps when diagnosing electrical in the Z's.

Steve, Thanks for the shout outs, I'll take 'em where I can get 'em. It's never a bad idea to pull the fusebox and give it a De-Oxit bath. Or scrub it down with baking sod or what ever that is.

The PLH will improve and already working system but will only improve the power output to a bad circuit at the same time. So make sure it's fixed before installing a PLH or HLH.

Dave

[SteveJ]

Well, Scott had the battery charged when I returned today. That helped a lot because I could do my debugging on a operating system.

Scott also bought the MSA fusebox. It looks great but he said the old cover was too small to fit over it. Has that been the experience of others? He installed the fusebox, and I went back to re-establish my earlier findings.

With the new fusebox, I only found the dome light circuit drawing power. That made sense since the doors were open and the glovebox was open. I suspected that maybe I was confused about which circuit I was looking at the previous week. (That's why I hate testing systems that I can't power up.) I confirmed current draws with a clamp on ammeter. The ammeter confirmed that there were no unusual current draws in the system.

For those of you who don't work with electricity much, a clamp on ammeter allows you to measure current without breaking the circuit to add the meter. The one I was using had 40 amp and 400 amp ranges. While it is not as precise as a meter installed in the circuit, it is not sensitive to polarity, as it will just display a negative number. The brand meter that tends to be the least expensive is Extech. You can search for their meters on Amazon.

Next we tackled the lack of turn signals. I found one wire pushing out of the harness, but otherwise, there were no signs of shorting or damage. Scott had replaced the turn signal switch with a reconditioned one. (The old one had been repaired once already.) We had the car on and tried the circuits with no flashing. I checked for voltage, and the circuit seemed to have 12 volts everywhere. We spent about an hour or so looking for why the blinkers would flash. (The hazard lights worked fine, separate circuit, etc.) Finally, I suggested that we just replace the flasher unit. We went to the parts store and bought a replacement. We plugged in the replacement, and all was well.

What I failed to do earlier was to look at whether or not the turn signals came on steady. (The flasher unit showed 12 volts to ground on both terminals.) Apparently, the flasher unit fused shut, so it couldn't blink. So now it appears as though Scott has a healthy electrical system in his car.

Thanks for the previous suggestions. I think it was more a matter of me not trying to out-think myself.

By the way, Scott got a tremendous deal on a great car, and I'm looking forward to seeing the car on the road.

Steve