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awolfe

1977 280Z Voltage gauge "Always On?"

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I am new to this forum and to the Z community, and in need of some help. I am currently rewiring my Z from a complete "Hack" job the previous owner did.

1. The original engine compartment wiring harness has been replaced with one from an automatic transmission model (mine is a 5 speed manual). Will this make any difference? I did find a few modifications that i had to make, ie...bypass starter relay, reroute inhibitor switch wire to back-up lamp switch, etc...

2. Is the Voltage Gauge supposed to be "Always On" even when the car is off and key removed from ignition switch? If so, wont that drain the battery? And, Is there a modification that will only allow it to be on when the key is turned to the on position (not acc).

3. When changing to an '82 model alternator, will the brake warning relay modification (yellow wire to Green-Blue stripe) have any effect on the fuel pump itself?

4. The 4 fusable links in the engine compartment have been replaced with custom "home made" ones. What is the correct gauge wire for these? And is there a specific type of wire that needs to be used?

Thanks in advance for any/all the help!

Also, A major THANKS! to the member who took the time to create a color wiring diagram for our Z's. It made my rewiring job so much easier and faster.

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In theory a voltage gauge has infinite resistance. In practice, it's almost infiinite. One of the few things I remember from my classes on electronics. The current draw is tiny. So, yes, the gauge is always on and won't drain the battery.

I was recently comparing ECU numbers and found that the 76, 77 and 78 Manual transmission cars all used the same ECU, #A11-600-000. But 77 and 78 Autos used A11-601-000. So there might be a wire or two to the ECU that your ECU won't handle correctly. Just something to be aware of if you run in to a problem, I do not know what the ECU differences might be. I got the information off of various other sites.

The fusible links have a high temperature flexible insulation so that they don't melt externally when they go. A lot of people replace them and the mounting base with Maxi-fuses.

Edited by Zed Head
Misspelled a word

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In theory a voltage gauge has infinite resistance. In practice, it's almost infiinite. One of the few things I remember from my classes on electronics. The current draw is tiny. So, yes, the gauge is always on and won't drain the battery.

This is correct, the voltage ga. is measuring the circut potential, or voltage of the charging system over a huge resistance. With such high resistance there is almost no current flow, which is what drains the battery. If I remember correctly, the clock is also on the same Pos. as the Voltage ga. and is not on the key. But my car is a 73 and perhaps not the same so I'll shut up now.

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IIRC, only the 76-78 280Zs had a voltmeter so the voltmeter in you 73 has to be aftermarket. The 280Z the voltmeter, thought it's unswitched like the clock, is on a different circuit, fifth fuse down, right side, while the clock is on the third fuse down, right side. But yes, the voltmeter would be 'always on'.

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So, what everyone is saying is that the voltage gauge should always be showing a 12+V reading even thought the car is off and key is out of ignition?

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Yep. That's what saw prior to turning the key whenver I jumped into my 78 for the 12 years I owned it.

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Thanks for the quick responses, Is there a way to modify to only come on when the key is turned to the on postion?

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IIRC, only the 76-78 280Zs had a voltmeter so the voltmeter in you 73 has to be aftermarket. The 280Z the voltmeter, thought it's unswitched like the clock, is on a different circuit, fifth fuse down, right side, while the clock is on the third fuse down, right side. But yes, the voltmeter would be 'always on'.

I stand corrected, I've got an amp meter.

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Thanks for the quick responses, Is there a way to modify to only come on when the key is turned to the on postion?
Anything is possible. All you'd have to do is find the wire that is the 12 volt source for the voltmeter and move it to the a switched 12 volt source. But why would you want to do that?

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I'm just not keen on the idea of too many things drawing from the battery when it is off. Odds are, if you say its suppose to be that way, I will not change it but would like to know there is still another alternative.

Thanks again sblake01 for all your help. Btw, would you happen to know about the fusable link problem i posted about?

4. The 4 fusable links in the engine compartment have been replaced with custom "home made" ones. What is the correct gauge wire for these? And is there a specific type of wire that needs to be used?

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The aren't wires per se. They are fusible links. The front box should have an 80 amp link closest to the fender and the other three are 50 amp as in this picture from the Alantic Z site.

post-3797-14150813755705_thumb.jpg

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Easiest method of turning it off is to detach the +ve battery lead.

Very counter-productive though. Best leave it as use it as it was design for.

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Awolfe, what everyone else said. I, too, was surprised the V meter always stays on. IMO the current draw isn't infinite or near-infinite, but it is very small in relation to the huge battery. It shouldn't pose any significant battery drainage problem, any more than your clock or the memory on your stereo. In fact the battery would probably lose voltage faster on its own than through drainage by these tiny circuits.

You can get fusible link wire from your local auto parts store. Off hand, I don't know the proper gauges or ampacities, but that info is buried throughout this thread:

http://www.classiczcars.com/forums/showthread.php?t=35588

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I didn't realize that the voltmeter in the later cars was always hot. At first glance that would seem like a problem, however generally analog meters have an input impedance of 10,000 to 20,000 Ohms per volt, so with the scale showing a maximum reading of 16V that comes out to somewhere in the range of 160,000 to 320,000 Ohms. At 12V that calculates to a steady state load of 38-75 micro Amps. At that discharge rate it would take more than 10 years to discharge an 800CCA battery.

So I would say it isn't a cause for concern.

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Somewhere I remember reading that the voltmeter was actually a "Battery Condition" meter.

Hence the coloured segments on the scale.

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I switched out my ammeter in my 73 to a voltmeter from a 280. To me the voltmeter tells me a lot more about battery and alternator condition. and yes. It shows on all the time.

Just lately my autozone lifetime alternator went bad. I've got a zx one that I'm going to go back with. its autozone lifetime too. came from my rustbucket 81zx.

don

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Thanks for all the quick and great advice, I decided to keep it wired as is. The previous owner was a complete nut job and made such a mess of things that i spent 2 days completely rewiring the car.

BTW, does anyone know or have a picture of the proper turn signal/light & wiper control location on the steering colum. I forgot to mark its location when i removed it to resoldier a couple of broken wires.

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Put the cover back over the steering wheel. It becomes obvious where the combo switch and turn signal switch need to be mounted.

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Personally, I much prefer an ammeter. I can tell when the battery is dead, knowing that it is headed that way is of much for help.

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I think you'd be in the minority. An ammeter can only measure the amount of current to the battery for recharging purposes while a voltmeter directly measures the entire charging system's performance. Has any auto manufacturer even equipped a vehicle with an ammeter since the mid 70s?

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Leonard, when your voltmeter reads anywhere north of, say, 13v, your alternator is maintaining the charge. So if my voltmeter were to drop from its usual 14.5 to maybe a steady 12.5, irrespective of RPM, I'd know I was slowly discharging and that my alternator wasn't doing anything. Besides that, there's a little alternator fault light on the 280's voltmeter, and that will probably grab your attention faster than an ammeter needle.

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I listen to my fuel pump to tell the state of my charging system. It even tells me when my blinkers are on.

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