How to wire my ammeter?

Actually, thats only half correct.

The portion of the wire that runs from the alternator to the ammeter is eliminated.

The other half, the portion from the ammeter to the battery, is still there as it's what you use to power your vehicle.

 

Yes, you're right.

I think one reason that some of us are prejudiced against ammeters, is because we see such creative wiring, like the SW add on ammeter I saw in a 55 Tbird that was wired with lamp cord. Better safe than sorry, so the shotgun approach is to say NO to ammeters.

 

I second that! If your new to wiring forget ammeters period. If you know what your doing then the feed is already protected for short circuits and should not be a problem.

 

My amp meter does not show oil pressure

 

The loads are connected to the system BEFORE the ammeter. A full-fileded alternator will dump it's current through the ignition switch, light switch, fuse box and anything else like power seat and window relays if they're enabled, BEFORE it hits the ammeter.

the battery, being 12 volts above ground potential, will draw less current than a radio, heater, a-c compressor, light bulb, etc. The ammeter will be the last thing to go south when an alternator full-fields.

It's only after the alternator has toasted everything else that the battery (through the ammeter) looks like the best path to ground.

 

Depending on where you have your volt meter tied into teh system, you can be as much as 1.5 volts below what's actually "in" your system.

Another consideration is what kind of battery do you have? Lead acid, low maintenance, maintenance-free, Gel, Hybid? Each one requires a different charging voltage. 14 volts on a lead acid battery means heavy gassing and explosion possibility. 14 volts on an Optima battery is barely enough.

Current, on the other hand, is a constant when it comes to monitoring an automotive charging system. One or two amps charge is all you want once teh starte drain is replenished. Anything else points to a problem. It's a simple as that. Regardless of the battery type, if it's more or less than 2 amps charge, you have a problem.

 

What I was getting at, is that alternators do not generate current, they generate voltage. You can't force current into a load! you can only force voltage into a load, and the current the load draws depends on how much resistance it has.

Sorry, my engineering background might be getting in the way of this discussion.

 

But a full-fielded alternator is capable of putting out nearly 20 volts, some hotted up ones will even go higher than that. Given that the resistance doesn't change, what happens to the device when too much voltage is applied?

 

That depends on the device, doesn't it. Some will short out and draw a lot of current, others will blow out and draw none, others will keep working and draw a bit more current.

 

Yup. The wipers will burn out. The headlights will burn out. The stereo will burn out. The cruise control will burn out. The heater will burn out. The MSD may or may not burn out, probably will last for a little while but you never know with those things. Same goes for a stock HEI.

Your engine management computer will go south and your engine will quit. If you're not running a computerized engine the battery, probably the only thing besides the coil that isn't an open circuit, will swell up so big you won't be able to get it out of the battery box if it doesn't explode first.

For the most part, if you don't catch a full fielding alternator right away, especially if you're on the interstate with the alternator spinning at a good clip, your electrical system will be toast.

If you've opted for a high-current affair to power that massive electric fan to keep your Mallory distributor-equipped SBC cool while you tool around the fairgrounds with the a-c and tunes on, you're looking at a pretty quick demise.

If, on the other hand, you have the vacuum advance set up right and your engine runs cool enough that you don't need that fan all the time, you can get away with a 35 amp generator and not have all these issues.

 

On big machines the way is to place a buss link between the battery and everything else, a buss link with known resistance.
Across this buss link a little DC builds and is polarized by current direction.
Buss links "shunts" aren't free, I don't know how to get one free, it probably wouldn't help with the old meter