advice on making a volt gauge please

[MrPants]

i suspect that my alternator is not charging the battery properly. i would like to be able to check it at any time (esspecially while driving).
i was thinking that i could run some alligator clip wires from the battery through the firewall into the cabin and then test it with my multi meter while in the car. that seems like a hassle.
so this is my question(s): is there any where at the fuse/relay board that would give me an accurate reading of the battery voltage? do any of the unused relay slots get full power from the battery? should the voltage at the battery with the car running vary at all or is it constant?
i am highly uneducated on all this electrical stuff so any advice would be greatly apprecited!

[bearone2]

you need to take it from the battery. make some long cables, don't crimp them as you close the hood and connect to the digital/led volt meter. don't use a volt meter with a needle unless you have to.

[SoCal Driver]

One of the large red wires that connects to the positive terminal is the main buss feed to the fuse/relay panel.

If you clean the battery connections up including these wires you can use the 30 buss on the fuse block.

This way you only need to run a ground wire from the battery.

Then if you clean up the ground to the chassis from the battery you could connect the ground side of the volt meter to a grounding point under the dash.

[MrPants]

Originally posted by SoCal Driver
If you clean the battery connections up including these wires you can use the 30 buss on the fuse block.

i dont know the proper terminology. where is the "30 buss"?
im looking at this and it looks like that thinner red wire you mentioned goes to the DME relay (connection 2 on the "fuel pump relay" in the picture). am i reading that correctly?

will i get a proper voltage reading if i connect the negative lead from multi meter to the body or does it need a direct connection to the battery?

[Porsche944]

Remove the center console gage cluster and disconnect the clock. Make a splitter and run the extra leads up to the center speaker grill. Mount the voltmeter in the center speaker grill. Reconnect the clock and reinstall the center gage cluster.

[SoCal Driver]

Originally posted by MrPants
i dont know the proper terminology. where is the "30 buss"?
im looking at this and it looks like that thinner red wire you mentioned goes to the DME relay (connection 2 on the "fuel pump relay" in the picture). am i reading that correctly?

will i get a proper voltage reading if i connect the negative lead from multi meter to the body or does it need a direct connection to the battery?

The "wire" I mention is the top one of the five horizontal "lines" on the schematic drawing. This is actually a thick copper stamping that is part of the fuse/relay block assembly. One of the heavy red wires from the positive battery terminal goes directly to this buss. It's hot all the time.

The #15 buss is from the ignition switch. It is only hot when the key is turned on.

You can use a 12 volt test light to "see" the 30 buss. Connect the test light lead to a ground point and use it's points on the fuses. There are several that are always hot. The cooling fans are one of these.

Even if you go directly to the battery to source a volt meter you still have to use the connection terminals on the battery. If these are not clean then you will not get a true reading.

Get a VDO volt gauge. There are ones that will match your existing gauges. I have one in a box some where that I will eventually install. Also an amp gauge. Though a digital display mounted in the center speaker grill showing this info is a better idea.

[singpilot]

There are voltmeters that plug in to the cig lighter. Funky, but they work.