Dan - If your old Corvette is a C1, then I have nothing to add. If it's a C2, it's BATT gauge carries only a very small current and is not as hazardous as gauges that carry the full output of the battery/alternator.

It is a battery gage but outside of the Corvette world I wasn’t sure many would understand the term. I wasn’t sure how much juice was sent through it. They have voltmeter conversions for them too, based on the same stories of dangers from the original gage - possibly overblown.

As I understand it, the C1 amp gauges actually carry a lot of current like the Cobra gauge you've been discussing. The C2 gauge connects to the wire between the alternator and the buss in the engine compartment at two different places. The very small voltage difference between those two points is what it senses and displays. It can be disconnected and everything else continues to work normally. . . My C2 is far from stock and I modified my instrument panel to include a voltmeter rather than the BATT gauge.

Patrick,

This one of your better suggestions.

I plan to wire it into 838 as part of the initial build.

John

Could anyone possibly make a schematic for this shunt I have an EM so my wiring is different, I already had to replace my amp gauge because it overheated, or should I just convert to volt gauge? I assume any ignition hot wire could be used for the volt gauge? Thanks

Take a nice picture, with a reasonably high resolution, of your engine compartment kind of from overhead, and I'll draw you the connections on it. I mostly want to see the alternator, the starter solenoid if you have one (and I mean the little four post FOMOCO solenoid that mounts to the firewall or fenderwell, not the starter motor) and the battery. The easiest, safest, and for surest method is to run a 10 or 12 gauge wire from the alternator to the battery connection at the starter solenoid.

Your ammeter has two main terminals. Each one has one (or more) heavy wires. All you do is add the shunt wire from one main terminal to the other, leaving all the other wires in place.

If you have male spade terminals on the gauge, each end of the shunt wire must "Y" and have a male and female so that the original connections can be retained.
https://erareplicas.com/427man/wirin...th_w_shunt.jpg

Correct. A key on 12v wire can be connected to the volt meter, and a good ground.

I've been perusing this thread as I have an ammeter issue similar to that noted by the OP and have a question about this shunt wire, which I'll eventually get to.

My SPF ammeter started a constant flickering on both sides of 0 last driving season with no correlation to electrical load. It was just a constant flicker from the time I started the car until the time I shut it off.

I noticed this behavior after having replaced my 11 year old battery, so began troubleshooting there. A load test on the battery says it is good. The battery reads ~14 volts after taking a drive. I have checked and changed battery terminals (they are marine brass) and am confident they are good. The battery ground is good, as is the engine to frame ground. I also added a 12 gauge ground between the VR and the engine block.

After all of the above there is a new symptom; the ammeter needle will occasionally flicker as initially noted, but then read more normal for a bit before taking a nose dive out of sight past 50- and then back to ~0 where it will read normal before starting the behavior all over again.

At present I am running 12 gauge wires from the battery to the cockpit so I can put an analyzer on it to see if there is any change to battery/charging that corresponds to the ammeter dips. Planning to do that test hopefully this weekend.

As to the shunt, am I correct in understanding this is simply a 12 gauge wire from the battery post on the solenoid to the battery post on the alternator? And doing so will route some current away from the ammeter to hopefully get a more normal reading from the gauge (assuming I have no other issues)?

I'm not much with electrical issues, so appreciate any assistance . . .

Chuck

Well, kind of.... Putting a wire from the solenoid to the alternator will bypass the ammeter, but it will bypass other stuff as well. If you look up at Bob P.'s post with the picture of the shunt wire he has it as just going from one post of the ammeter gauge to the other post of the ammeter gauge -- that's like a three inch wire. That's a true shunt wire. I prefer to run a wire from wherever the first convenient connection is on each side of the ammeter which, for me, happens to be a circuit breaker connection and a fuse box connection both on the engine side of the firewall. But that's on an ERA, every manufacturer is different. OTOH, if my ammeter was really, super-duper easy to get to, like being right out in front of my face, so that I didn't even have to bend my back, much less crawl under the dash like an eel, then all I would have done is exactly what Bob's image shows.:cool:

Ahh, okay. So it would seem that I mostly understand what is being done here but I, much the same as you just described, try to refrain from under-dash exploits as they generally end up causing more pain than it's worth. Appreciate the response Patrick, I'll have to give it all some thought after I do a road test with an analyzer to see what's really happening with my charging system.

Chuck

I see you ran an extra ground to the voltage regulator, which is good, and poor grounding is the #1 cause for a varying voltage which would make for a varying current which would cause your ammeter needle to waver. Just to be absolutely sure though, get a nice four foot long wire with alligator clips on both ends and put one on your voltage regulator case and the other on the negative post of your battery, then see if the wavering is still there. If so, confirm that your voltage at idle is really bouncing around and up in to the 15 volt range, which it shouldn't. Generally when that occurs it's because of poor grounding at the voltage regulator and I'm still suspicious of that.

Makes sense. One more item added to the weekend to-do list. Thanks!

Chuck

I had a few hours today, so did a little more testing.

I had previously run a ground wire from the VR to the engine block, but this time also ran a temp ground between the battery and VR. The ammeter kept up its' constant flickering even with the extra ground.

Being slightly impatient and better at the shotgun approach as opposed to logical troubleshooting, I replaced the VR with a new one and ran a single new, permanent 12awg ground from the VR to one of the bellhousing-to-block bolts. I then pulled, inspected, cleaned and re-installed the battery to frame and engine to frame ground cables (something I had already done last fall).

With my analyzer hooked up in the cockpit, I started the car to see what I had. For the first time in a long time, the ammeter needle was steady and, after some initial charging from the startup, hovering just to the right of center at a fast idle. The analyzer agreed with that. Going down the road I was getting a constant ~14.5v reading on the analyzer and the ammeter rock solid to the right of center. Running a load (headlights and heater fan) there was a brief dip, but then right back to right of center and ~14.5v.

This was a fantastic turn of events until 10 minutes into the drive, the ammeter dropped to 25- and my analyzer agreed, having dropped to ~12.5v and continuing to decrease in small increments. Things continued to head south for 1-2 minutes, when both ammeter and analyzer went back to right of center and ~14.5v respectively.

The same phenomena happened twice more while out driving. All is working well when things take a 1-2 minute dump before returning to normal.

Any thoughts come to mind with this one? I don't have a new alternator to shotgun into the car, but am thinking about pulling mine and having it tested.

Chuck

Yep, pull the alternator and have it tested under load for at least 20 minutes or until it fails, whichever comes first.

It took a while, but I now know my alternator was failing. I bought a new PowerMaster 7078 75-amp unit, installed my serpentine pulley, installed the alternator and tested the car.

No more flickering ammeter, the battery is in a constant state of charge when the car is running and the ammeter gauge will drop slightly when additional load is added. It's perfect!

Hopefully the really cool weather can hold off until I get a few miles on the thing yet this fall.

Appreciate the assistance Patrick . . .

As Mr. Mustang is fond of saying, "I am here to serve others.":cool:

Is this with or without the supplemental shunt wire installed?

I do not have a shunt wire installed, at least not yet. It's still on my list of potential winter projects though . . .

Chuck