Where to tap for voltmeter?

[evilnickwong]

I'm gonna install a voltmeter soon. For it's light, I'll just tap into any of the light wires around the center console/dash area so that it can dim along with the other lights using the knob.

But where should I tap for the signal?
Can I just use any random 12v ignition source, or must I get it direct from the ignition column? If not, then where's the most convenient ignition wire to tap into?

Also, if I tap to a acc. wire (e.g. radio or glove light), I read that I won't get a reading during actual ignition/starting of car and thus cannot see my startup voltage. Is this true?

[Aptyp]

Right on the firewall where the power distribution is. Right over where engine harness goes into firewall.

[evilnickwong]

That would be on left side of firewall right? (driver's side for LHD car).
Which wire specifically, is there a single color for it?

[StereoInstaller1]

If you want to see the actual voltage drop when starting, you would want to catch actual voltage off of the ignition wire.

IIRC, it is green and in the ignition harness.

Needs to be live in run and start.

Luke

[evilnickwong]

OK got it thanks.
Otherwise, if I connect to an acc. wire, it won't give a reading when starting, but thereafter when running I can still monitor it, right?

[StereoInstaller1]

OK got it thanks.
Otherwise, if I connect to an acc. wire, it won't give a reading when starting, but thereafter when running I can still monitor it, right?

Yeah, you go it.

[b*saint]

Just if you wire it to the ignition wire make sure its parallel not series. Your volt meter will NOT handle the amps and WILL go up in flames as happened when my friend wired up his own horn in series with the ignition coil.

[delatlanta1281]

Meh
mine is on my accessory wire. Works fine.

[AndrewBird]

Just if you wire it to the ignition wire make sure its parallel not series. Your volt meter will NOT handle the amps and WILL go up in flames as happened when my friend wired up his own horn in series with the ignition coil.

It took me a second to figure out what you are talking about. Your friend basically put the gauge inline with the ignition? Yeah, that's a no-no. All you need to do is tap into the ignition wire, run it to the gauge, then ground the other side of the gauge.

[evilnickwong]

OK so I decided not to cut into my ignition harness, but took power from the wire that powers the glove box light instead. (the electrical manual pdf says that's active in acc, ignition + run)

I get these readings:
Ignition on, engine off - 12-12.5V
During crank - 10.5-11V
Engine running + audio, etc - 13V
Engine running + audio, etc + headlights = 12.5-13V

Are these readings OK? Or is there an inaccuracy taking readings from the glove box light wire? (I tapped into the wire before it reaches the light bulb socket, and the voltmeter is grounded to the cigarette lighter ground).

[Schnitzer318is]

Looks fairly accurate to me... My megasquirt readings are about a half a volt higher than yours for all conditions. I'm running an optima red top though... might help the charging system a bit.

[evilnickwong]

Thanks to all for helping a wiring noob out. :D Learning more each time I play around with my multimeter haha. Here's my finished install: