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just got a volt guage and it says to put the negative lead to the batery and positive to a 12v power supply. dont fancy hacking up my ignition or ciggie lighter wireing soooo...
could i just send the wire to the positive on the coil?

Why not just wire direct from the battery?

Because if you wire voltmeters (or anything else for that matter) directly to the battery, you'll have a small but constant drain even when the alternator's not charging it, which is the kind of thing that leaves you with a flat battery if you don't drive the car for a few days

I've experienced this by wiring my radio directly to the battery. I turned it off when the ignition was off.. but it still drew a small current just telling the radio that there were power there, and kept on flattening the battery until I realised what was wrong A voltmeter would do just the same.

Just chain it off the back of the ciggarette lighter. Don't need to hack up any wiring, just solder a new wire to the terminal which connects to the ignition wire.

A voltmeter would use the tinyest amount of current. (something like 1mA) but it depends on the voltage and the resistance of the meter. Such a small current would take years to drain a car battery. If your radio is flattening ur car battery in a matter of days then I would be suspicious as Radios dont use alot of current when theyre switched off (they just keep the radio presets). But ur right, it would be nice to see the voltmeter jump up when you switch the ignition on.

A digital voltmeter would use a negligable current.. but analogue voltmeters (as I'd imagine this would be) tend to be basically a direct circuit across the battery with about 500 ohms resistance.. it wouldn't draw much, but it's enough.

As for the radio, yeah, I was suspicious about that, it seemed to be drawing a fairly decent amount of current considering it was just on standby.. but hey, it's sorted now, not going to worry about it

hey guys, cheers for the replies.
yeh its an analouge clock. was gonna plug it to the positive battery terminal but like gareth said, id like to see it jump up when i switch the car on.
i hear what u mean about soildering it to the ciggie lighter only i cant be arsed with the pulling the centre console out and my solderings not up to much. maybe ill leave it till i can be bothered
thanks again

You could maybe find some way to run the meter off the 'ignition' power line on the radio connector with some kind of power splitter or piggyback connector? There should be 'constant' and 'ignition only' pins on the plug (like, one to save the battery backups, one to run the amp when the engine's on)

having said that... i've got mine switched to be constantly on because 1. it's got a bug, and the presets & settings vanish if the key's off more than a day or so 2. it switches the amp off anyway when i remove the face panel or hit the "off" key (but removing it also turns off the display )
still a bit of a drain though as it's in standby rather than merely "preserve memory". the car isn't left standing more than a week at a time though, so forgetting the lights is a bigger worry (as is that analogue clock built into the dash pod )

don't know whether the voltmeter would be even as much a drain as that - depends how it's set up. the little hand-held battery checker thing i got for £5 is a mega drain, if your AA battery is only 1/8 full it'll flatten it within 30 seconds.... I would suspect a car voltmeter to be a little less severe however, and of course, your car battery has about hundred AAs in one (12v ~65Ah vs 1.2v ~650mAh) and remains mostly full a lot of the time.

be worth carrying a spare if you've got one though, just for the first month.

i was just thinking of running it off the radio but in the end sent the positive to the coil. and would you adam and eve it she works, couldnt be arsed to work out the positive lead on the light switch though so pluged that into the coil as well so the lights on all the time the ignitions on. ah well, at least its in