should volt gauge always be reading?

[dcruz]

Fellows I have a question, I have painted the 1978 280z and about to start putting it back together, I also changed the face gauges and I just noticed that when I connect the battery the volt gauge read the voltage of the battery, even when the car is turned off is this normal for the volt gauge to always read voltage? I didn't noticed this before I took the voltage gauge because it wasn't working but once that I put in the new indiglo face I fixed it,simple fix, the needle was hitting and wasn't allowing it to move, Any way i'm just concern about it reading voltage even when the ignition is turned off. Thanks for your help.

[78zcar_blue]

Hello,

Yes, the voltage gauge should always display the voltage even with the iginition off.

[dcruz]

Thanks for the reply just making sure, didn't want the battery to drain, or put everything back together and find out that it shouldn't be reading when the ignition was off. Thanks you very much.

[FastWoman]

dcruz, the voltmeter has a weird design. It's actuated off of the ignition circuit. Power from that circuit heats a small coil, which causes a bimetal strip to flex and a contact to close (inside the volt/fuel gauge). With that switch closure, the gauge is connected into the battery circuit. In short, when you turn off the ignition, the coil should cool, the contact should open, and your gauge should read zero. At least that's what mine does.

The circuit is probably overly complex. If your bimetal strip assembly isn't switching correctly, you might just power the gauge off of the ignition circuit. The wire already runs to the gauge. All you'd have to do is to route it to a different pin. If you wanted to get fancier, you could recreate the circuit by using a simple 12VDC relay from Radio Shack in place of the bimetal switch. I wouldn't put it inside the gauge housing, though, as stray magnetic fields might make the gauges inaccurate.

[sblake01]

Sarah, if that's true either something is wrong with or your gauge or the circuit has somehow been altered. My 78 as well as every other 76-78 280Z I've ever seen reads the actual voltage at all times even when the ignition is off. My 79 810 did so as well. The voltmeter is (or should be) directly linked to the batery through a fuse and fusible link

Edited November 22, 2010 by sblake01

[FastWoman]

Steve, you're right. (My bad.) I must be slipping, because you'd think I'd notice that my volt meter is always on. I usually notice those things.

The FSM schematic does show both IGN and BAT lines feeding to the combination gauge, and they describe the thermal switch. Unfortunately their schematic is somewhat unclear. I had assumed the IGN switched power input from the BAT circuit to the volt meter. I'm uncertain what the little thermal switch is all about. I'll need to look back at the FSM to figure that out.

How much current does the little gauge draw? Anyone know? I'm guessing maybe 50 mA??

[sblake01]

It can't draw much. One thing I remember about my 78 is that even if I went two months without driving it, it always started right up. I can't go two weeks with my GTO....

The voltmeter on my daily driver Ranger only registers when the key is on

[dcruz]

Hey guys, sorry for the late reply I just read 78 zcar blue post and assumed that the thread was concluded, any way the reason that I also asked was that my daily driver 96 mustang gt, only reads when the ignition is on. Thanks for all the help, this forums are great, I have done many things to my z thanks to this web site. Thanks again