Best place to wire up a voltmeter?

[Snitzler]

I deleted the radio and had one of those radio delete plates installed and then I saw a picture from McLaren-TAG. I already had the same voltmeter so I decided to do the same. Where is the best place to wire the voltmeter to? I found a bunch of different suggestions and would really like to stay away from the ignition switch. Somewhere off of the fusebox? I need power for the light as well, off of the instrument lights? I guess fuses are in order as well. Clueless in electrical land....

[SpyderMike]

power it using the radio wiring...the green wire should be switched to allow power in ACC or RUN positions of the ignition switch. The lights can be daisy chained off gauge lights (Black Blue wires). If you don't want to use the ignition switch, then there should be a red constant powered wire to the radio that had a fuse in it. You can switch that source back at the fuse panel to a switched bus (however, that switched bus still ultimately comes through the ignition switch). The general power scheme on these cars is that pretty much most power is distributed through the ignition switch.

[SpyderMike]

Here is a brief on the ignition switch power distribution:

understanding the ignition switch

I redistributed my car's power completely because with the aging connections in the car, and the systems that were added over time by Porsche to an old wiring design I was concerned. Some circuits were simply not protected at all.

[911tracker85]

hopefully Dennis will rectify all of the short comings of these wiring harnesses when he builds me a completely new, custom one for my 78 930 project.

[7783911]

I ran directly from fuse panel for power (position 5 I think..switched) and then a ground from the bulhead behind the blower cover. Threaded wires throough small grommet and mounted volmeter into my center console. Picked up another ground and power from clock using piggy back connector to light up the dial

[famoroso]

Scosche used to offer a $7 harness that plugged into the factory radio radio harness. If it's still available, I'd go with that.

[Snitzler]

When I deleted the radio, I bundled all the wires from the radio with heat shrink. I found the switched power wire (green) and I am using that for the voltmeter. I just have to tap the lighting wire from the clock and I can finish the installation. I think I should fuse the lines. What fuse value should I use, 5 amps? Thanks for all the advice.

[Duc Hunter]

I am not sure its is really that important. In my experience the alternator keeps the voltage basically the same across the car. On mine I can see when the electric A/C kicks on, headlights, etc. The idea is not to measure to the hundredths of a volt, it’s to show you bigger changes in the system like a bad voltage regulator, or a broken fan belt, etc. Don’t over think it in my opinion.

Great panel by the way. I did something similar in my Rat Rod.

[SpyderMike]

You fuse for the gauge of the wire...you are trying to keep the wire from melting. Smaller is safer. I would start out with 3 amp or something.

[Snitzler]

Well its done, before and after pics. I think I will have to glue in the plate, it is a little loose. I haven't wired up the light on the gauge yet, that is for another time.

[7783911]

so what was the difference in hole opening size between original swicth and 2.25 vdo gauge?..who did you cut of you needed to?