I did something I'm no too comfortable with all of a sudden. I'm using the IGN terminal on the fuse block to power my HEI so I thought it was a simple solution for the voltmeter as well (sunpro gauges). I pig-tailed them together and soldered them up nice but now I'm wondering if that's a bad idea. The voltmeter reads a hair over 14v and she seems to run fine, but still.....
Thoughts?
Should I run a wire directly to the bat terminal on the alternator for the voltmeter? It's externally regulated. I looked and looked under the dash but couldn't find the oft-suggested gray wire.
EDIT: Now I'm confusing myself. The gray wire is for the lamps w/dimmer I think.

 

The gray wires are dash lamps. I would hook it up to a 12v keyed source, however its such a light load that its probably fine where its at. I used my radio power wire.

 

Use radio or just plug it into an acc part of the fuse block

 

Any post on your fuse block that is live with the key in the Run position will work fine.

 

That's the issue Randy, I only have the one post and a couple of empty bays.
(other) Eric, do you share it with your radio?
I'll probably leave it for now and see what happens.

 

I just tapped into the wire that fed the radio. It really doesn't matter where you connect it as long as it has power only with the key on, it draws very little current.

 

What made you uncomfortable?

 

I'd run it out to the horn relay that will give you the most accurate reading. All the power goes through the horn relay that's where you should be reading it.

 

IMO, you should never hook anything to battery power than can short out. Can you say smoke & possible fire? You can piggy back on to any fuse on the block that is hot in Run. A voltmeter draws virtually no current at all. Be sure to tap on to the fused side.

 

Not sure, gut feeling. Something about the HEI being a high power output unit sharing it's input. But it was just a feeling not experience.

So I have to admit I don't know how to tap the fuse block. Is it tapping into the wire on the backside of the block?

 

Well stated
The current draw of a voltmeter is about zero, by definition...
if it passed much electricity it would be an ammeter.

 

Tap = hook to.

 

Yes, but to the back? Not putting a connector on the fuse holder in front, right?

 

Yes, from the front. Auto parts stores sell a little connector, kind of like a male spade connector, that is curved and will fit in to a fuse holder - it is called a fuse tap.
There are more styles out there, just pick the one you like.

 

The key with a volt meter is to decide what you want to monitor, ie: where you want to connect it.
As stated, the power stud on the horn relay is considered the "zero point" so to speak, of the power supply system, so it is a logical place to connect. The supply on the back of the alternator makes, sense, too.

You can connect to any of these, and to prevent the chance of a horrible short, just fuse the voltmeter supply wire.

And, Yes, by definition, volt meters draw so little current as to essentially not be drawing any.

- Eric

 

The horn relay stud is not a keyed source and no one I know connects one there as it will draw a battery down over time.

 

You are completely correct.

Duh.

What was I thinking?

They are good sources to connect to, but not without putting a relay between the post and the meter, controlled by the ignition.

The fuse block can have a fair amount of resistance from subtle corrosion, so may not be the best electrical connection point, but tapping off of it in the right place (IGN or ACC lug, for instance) will give you switched, fused power.

I've always prefered a source switched to the ACC side, as it leaves the gauge on if you are sitting in the car running the radio, and you can see if the battery is draining down before it's too late.

Also, either of these can be very useful for this:



- Eric

 

As always Eric(s), the info is appreciated.
Umm, dumb question maybe but how do you know which end of the fuse is fused (output)? I would assume it's the right-hand side but I have nothing to base that on.

 

Pull the fuse, check for voltage on each end - the end with the voltage is before the fuse.

- Eric

 

That brings up a point I was thinking when I first read this earlier today: exactly what would you want to monitor? The voltage that the alternator is putting out or the voltage that your accessories are actually seeing? They can be different. If you monitor the alternator you may not be seeing the reality on the other side of the firewall, but you'll know what your alternator is doing. Does this really help you? Depends upon what you want to know, right? Is my battery getting charged, or are my accessories getting full power? If you monitor inside the firewall and have full voltage, then you know everything is OK. If you don't have full voltage, then you know it and can fix what's wrong.

 

No matter where you tap into with the key on, it will be within a few millivolts of what the electrical system is seeing. The voltage will fluctuate between around 12.5v and 14.5v depending on whether the lights are on and the alternating is charging.

 

Dang, why don't I think of these things?

Sometimes you guys think way too hard about this stuff. But then again, school starts next week so I'd better get back in that mode

 

This qualifies as a quibble, but if you have a lot of corrosion in your fuse box connections, you could have a 1 volt difference between there and the battery or alternator.

In my car last month, I found that my battery wasn't charging - I had 14.5V at the alternator, but 13.25V at the battery.
Grounds were good, but there were losses in the wiring from the alternator to the horn relay, from the horn relay to the starter, and from the starter to the battery.
I cleaned and replaced wires and terminals and now there's less than 1/10th of a volt difference, but the same thing can happen throughout the electrical system, and especially at the fuse box, where those steel terminals love to corrode.

My point? You could be reading 13V at a fuse box tap, think you've got a problem, and the alternator can be feeding 14.5V to the battery.

You can connect the volt meter anywhere, but at least check to be sure that you know whether your readings reflect the actual voltages you are interested in monitoring.

- Eric

 

he horn relay stud is not a keyed source and no one I know connects one there as it will draw a battery down over time.
You are completely correct.

Duh.

You are correct I have to double DUH.

 

Well as it turns out, I was looking for a bad connection that wasn't. Yes I was concerned about sharing the power source but the meter was also acting odd. Working sometimes and not others. I'd check for juice at the meter and sometimes it would have it and other times it wouldn't. I picked up some spade doublers and taps and that ironed out the power issue but I also discovered the meter is bad. I have to tap on it firmly to get it to read (which only works some of the time). Now, since I bought the triple gauge set I assume I either uninstall the oil and water gauges in order to return it or purchase the single voltmeter. Kind of a no-brainer but still.....

 

I would install the water and oil gauges. They are much better than the idiot lights.