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PostPosted: Sat Jan 09, 2016 9:58 pm 
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Location: CT
And if the diode dies the ignition usually refuses to stop the engine when you turn the key OFF, and the battery discharges back thru the alternator to ground to become flat overnight.

Also ~ if the battery is 100% fully charged, it has no need for further input. The regulator (or diode) detects that and shunts any excess power directly to ground, rather than 'cooking' the battery by trying to over-charge it.

As I'm sure you know, the battery's only duties are to (1) turn the starter to start the engine (2) to operate accessories when the engine is off, and (3) to supplement the alternator in those *extremely* rare occasions when your electrical demand somehow outstrips the alternator's capacity (if you had 30 floodlights or amplifiers or something). As soon as the engine starts, the alternator handles 100% of the electrical demand on the car. You could literally remove the battery from your car and drive it all day if you didn't turn it off.

Once the car has started, the alternator takes a very brief period to replace the used potential and bring the battery back up to 100% charge. After that point, the battery cannot accept any more charge, so the excess charge from the alternator is shunted directly back to ground, by design. Overcharging a battery will boil away the electrolyte until the cells are dry and the battery is destroyed. The reading btwn posts should not exceed 13v when the engine is off. When the engine is running, any higher voltage you read btwn the battery posts is the alternator power (because it's electrically the same measuring point as the output terminals on the alternator itself), not the battery's power. If you read 17v (for example), and the battery is fully-charged, any accessories you are running will take their share of that, and the remainder will be shunted to ground. You can't over-stuff a 12v battery by more than a few percent.

I just picture a fully-charged battery as a full pot of water sitting under a trickling faucet. The faucet keeps pouring water down to the pot but it can't make it hold more than it's designed to, so the excess water just spills over the sides. Same with an alternator trying to charge a 12v battery; once the battery is fully charged, the alternator could send 40amps to it, but the battery would just say, 'no thanks' and spill the excess charge directly to ground.

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PostPosted: Tue Jan 12, 2016 4:58 pm 
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Location: Orange, CT
Great explanation Frank
I did take the negative terminal off the battery while the engine was running and it died.
So is something bass ackwards?

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Nov/70 late series one HLS3014777 Sunshine Yellow 919


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PostPosted: Tue Jan 12, 2016 6:09 pm 
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If it doesn't run without the battery, the alternator is not putting out juice to the system for some reason.

I'm trying to picture what the "CHARGE" circuit in the MSA fusebox looks like, and if a mistake there could be causing all your problems.....

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PostPosted: Tue Jan 12, 2016 6:20 pm 
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Frank T wrote:
If it doesn't run without the battery, the alternator is not putting out juice to the system for some reason.

I'm trying to picture what the "CHARGE" circuit in the MSA fusebox looks like, and if a mistake there could be causing all your problems.....

Do you think something's not hooked up right at the box?

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PostPosted: Tue Jan 12, 2016 6:33 pm 
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I would only be guessing, but since the box is newly installed and all was right with the world before you swapped it in, I'd suspect something went wrong during installation.

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PostPosted: Fri Jan 15, 2016 3:03 pm 
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Location: Richardson, Texas
Here are some pics of the OE and MSA fuse boxes for our cars (since they are very close cousins). The wiring colors and plugs in the MSA box are identical to OE but they omit the large spade connectors and supply butt-splice connectors for the two high amp wires. The spade connectors on my OE box were still serviceable so I cut them off and moved them the new one. This is pretty much a plug-and-play install and if nothing else was swapped or changed, is not likely the cause of the problems.


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Fuse Box 01.jpg
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Fuse Box 03.jpg
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Fuse Box 04.jpg [ 389.5 KiB | Viewed 6990 times ]

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Jim Arnett
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HLS30-15320 12/1970 (original owner)
ZCON 2015 Gold Cup - Street Modified class
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PostPosted: Fri Jan 15, 2016 3:16 pm 
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Thanks, Jim!

The MSA box is SO much cleaner and easier to work with! There are few things which can go wrong with one, but a plastic connector might not fit right, the pin count might be different, a soldered connection might be faulty, or a fuse (or the fuse cradle) might not be passing current, even tho it looks good.
My MSA box plugged right in and everything worked, first try. But MSA was very specific about asking for my Z's build date. These cars changed SO often in the early years, there were electrical changes within the same model year, and the 35,000 1971 cars (Oct70-Sep71) seem to have seen the most-frequent changes. There's a possibility that your MSA box might not be the best one for your build date (different pin count, for example). I know the electrical components (switches,etc) for the 1971 cars would not work on the 1970 cars, and some early 1971 cars would not accept later 1971 electrical parts. When you're fighting an unseen Gremlin, you have to keep an open mind.

Let's do this rationally.
Run the car, turn on the headlamp switch. Pull the plugs off the back of the headlamps, and measure what you get to ground (be careful not to let the smoke out of your SparkOmeter). Technically, you could take the measurement with the car off, too.
If you don't get any reading (Zero current), we can walk backwards from there.
If you do read current (high and low beams), check your ground or replace your headlamps.

I undrstnd you're having multiple electrical issues, but this one seems to be the easiest to examine now. Instead of starting at the reservoir, let's first turn on the faucet and see if we get 'water' running out of it or not.

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PostPosted: Mon Jan 18, 2016 3:45 pm 
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Location: Orange, CT
Great write-up Frank and Jim!
That's super helpful.
I bought my fuse block off ebay so I don't know what it was specifically made for.
There's also no part number or any identification.
I need to isolate the circuits but it's too cold now.
I also had a rotted ash tree attack my shed last week so I'm dealing with that.
Image
Image

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PostPosted: Mon Jan 18, 2016 5:53 pm 
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:( About six or seven years ago another member (Dave, maybe?) had a tree fall thru his garage roof and *just* miss his Z. Nearly scared him to death. Bonked his windscreen if I recall correctly.
If that ever happens to my Z, I'll probably just hang myself.

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PostPosted: Mon Jan 18, 2016 6:14 pm 
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Frank T wrote:
:( About six or seven years ago another member (Dave, maybe?) had a tree fall thru his garage roof and *just* miss his Z. Nearly scared him to death. Bonked his windscreen if I recall correctly.
If that ever happens to my Z, I'll probably just hang myself.

Yea I know what you mean.
The dimensions I built the shed to allow me to store the Z if I need to.
Luckily I built it with a double top plate like a regular house, otherwise that multi-hundreds of pounds tree would have taken the wall down.
Nothing at all inside was damaged.

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PostPosted: Mon Mar 14, 2016 8:50 am 
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Location: Orange, CT
Update
After talking with the guys over at classiczcars I think I'm looking good on this subject and I now have 14.5v at the battery with some caveats but it's working.

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