Quick voltmeter wiring question:

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Quick voltmeter wiring question:

April 01, 2005, 04:31:14 PM

This question is sort of a rush job, since I'm in the middle of the project as we speak.

OK, I brought this up a long time ago when I installed my little gauge cluster.. my voltmeter was consistently reading 1-1.1 volts lower than my digital tester read at the battery. It was suggested (by jcassity, I think) that I run a wire right from the battery to the voltmeter. I wanna make sure this sounds OK before I put power back to it. Yes, I am very paranoid about electrical work.

Picked up some 12ga. wiring today, and an inline blade fuse holder. Smallest fuses I could pick up for it were 5A. I have a wire running from the battery side of the solenoid (I was more comfortable putting it there, sandwiched in between all the other connections on that side) in to the fuse holder and then right to the voltmeter. However, on the other side of the voltmeter is some of my old 16ga. wiring, running to a bare metal spot on the steering column frame.

Does this sound right? Something about it feels wrong to me.. about having a constant connection or whatever. (as it was before, it came on with key-on, because the power source was the power wire for the wipers)

Re: Quick voltmeter wiring question:

Reply #1 – April 01, 2005, 04:43:30 PM

If jcass said it then that would be good enogh for me

Re: Quick voltmeter wiring question:

Reply #2 – April 01, 2005, 04:49:00 PM

If you were half as paranoid about wiring as I am, you would be double-checking that you got it right no matter who said it.

My mother repeatedly told me a story about how her Grand Prix had an electrical fire when I was a baby, and the story put a healthy paranoia in me from an early age about car electrical stuff. So nothing personal against jcassity or anyone else, but I wanna make sure I did this right before I put power to it.

Re: Quick voltmeter wiring question:

Reply #3 – April 01, 2005, 05:06:20 PM

Quote from: Bird351

Does this sound right? Something about it feels wrong to me.. about having a constant connection or whatever. (as it was before, it came on with key-on, because the power source was the power wire for the wipers)

You needn't worry about your car burning down. The fuse will blow if anything downstream shorts out.
I would check out the parasitic drain of the voltmeter though. I have no clue what it is, but if it is more than a few mA...you'll drain the battery over a period of time. I think the maximum allowable from the factory is 50mA. My car pulls 11mA at rest.

Re: Quick voltmeter wiring question:

Reply #4 – April 01, 2005, 05:09:57 PM

Well, I'm thinking about getting a solar panel that plugs into the cigarette lighter, and I think it charges 100mA. It's only about $30 or so, if I recall. (brought it up in the alternator thread)

Alright.. took a moment to primer the instrument cluster trim from the other car while I waited for a response for this.. so I guess I'll go put power to this and see what happens.

Re: Quick voltmeter wiring question:

Reply #5 – April 01, 2005, 05:16:17 PM

What Jeremy said. The volt meter should have a very small current draw, so your 12-gauge wire is overkill (nothing wrong with overkill, though, it's underkill that hurts). You could easily get away with 20 gauge wire (or even smaller) for a voltmeter.

To check your parasitic draw, make sure everything in the car is off (including dome, hood, or trunk lamps). Disconnect the battery, and put an amp meter in series between the battery post and your disconnected terminal. Make sure the amp meter is fused! And make sure that you first test it on the 10-amp scale just to be sure that nothing is on. Once you verify that the amp draw is no more than 0.2 amps you can safely switch over to the "200 mA" scale and get your actual reading. Let the car sit for a few minutes before taking the reading to ensure that you're not seeing any "startup" current draw that may be higher than nonrmal. If your reading is more than 50mA you are at risk of the battery going dead over a few days.

Do NOT turn ANYTHING in the car on while you are doing this test. Do not even open a door or the trunk. Doing so will result in a current spike that could instantly toast your amp meter!

Re: Quick voltmeter wiring question:

Reply #6 – April 01, 2005, 05:45:49 PM

Well, I went thru all that change and.. no significant change. It still reads just about 1v low. 12.22v at idle from the battery when I first started it up, (after it kicked off fast idle) and 12.45v at idle from the battery after I took it for a drive of about a mile and a half. Readings of the gauge at both times: About 11.1v the first, 11.5v the second time. At least now the voltmeter is less reactionary to things like brake lights and turn signals.

Don't know if my little digital tester can do amps. I see VDC, VAC, an arrow pointing at a line, a K with the Ohm symbol, and CONT with an audio alarm. This is one of those little fold-up Radio Shack specials.. maybe cost me all of $10.

So either my multimeter sucks, or my voltmeter is off. *shrug* Wouldn't surprise me either way, both were cheap.

Re: Quick voltmeter wiring question:

Reply #7 – April 01, 2005, 06:19:12 PM

I would bet it's the voltmeter. If it's practical, take it outta the dash and connect it right at the battery to see your readings.

As long as you know the baseline it will still work for you. If it varies from the normal reading you'll know something's wrong.