Capt Ken

I've been studying the wiring diagram trying to figure out why things aren't working.

The diagram shows both leads to the ammeter being fed off the 12 post on the horn relay. One side is a Black/white wire that runs directly to the 12 post, the other side a black wire joins a red wire that has a tee to the 12 post and terminates at the battery post on the starter.

I know ammeters must be wired in parallel, but this just doesn't seem correct.

fanmanbd

I believe amp meters need to be in series.

7t2vette

An amp meter is wired in series not parallel.

Capt Ken

The diagram still doesn't make sense even with a series connection. How does it read the current if both leads of the ammeter are coming from the same post? It would make sense if the black wire went straight to the battery post on the starter and did not have a tee off the the horn relay post. what am I missing?

fanmanbd

The amp meter has to break the circuit to work.

noonie

It is wired in series, but in a parallel signal circuit so the full amperage doesn't flow thru the meter.
First check to make sure that you have voltage past each fuse link on the small signal wires when the ammeter is disconnected.

LB66383

To my knowledge, those vintage of Corvette "ammeters" (C2-C3) are actually voltmeters. It's a voltmeter that is measuring the difference in voltage between the alternator and the battery. If the battery is low and the ammeter is charging it, the ammeter voltage is higher and the needle goes to the right. If the ammeter is not putting out enough voltage, the battery voltage is higher and the needle goes to the left.

7T1vette

Well, the meter is actually a millivoltmeter. It is calibrated in AMPS because the meter is measuring the voltage drop over a defined length of the wiring harness that carries the current through IT {not through the meter}. The length of wire used is terminated by the ends of the leads from the meter.

So, you have a millivolt meter using a current shunt (length of wire in the harness) being used to measure a voltage drop over that length of wire, but shown on a dial face that is calibrated in AMPS. Did you get all that?

Capt Ken

Thank you. That makes sense now. The wiring in the car is a mess, lots of crimps, new wires added that don't match the color etc. Going to be fun?

Lots of stuff doesn't work. Fuses look ok, from a quick visual. Thinking it might be a common ground that might be the culprit. Is there one that is usually the cause?

Also anybody have a picture of a fuse link?

Peterbuilt

Also anybody have a picture of a fuse link?[/QUOTE]


http://www.madelectrical.com/catalog/fusible-link.shtml

What year is your Vette?

At the starter.


Here's the way the ammeter is connected.

7T1vette

The length of harness wire between points "A" and "B" [in above drawing] is used as the shunt for the ammeter circuit. The wire leads running from the meter to the fuse panel and then on to those "A" and "B" points have no impact on the circuit, other than to transfer the voltage drop over that shunt line back to the millivolt-meter.

Rewire per that drawing above, making sure the fusible links in the circuit are still good. If your meter is good, it should work just fine.

[P.S. To see if the meter is operational, just quickly touch a 1.5v battery to the meter terminals (do not connect them, just touch and release the jumper wires while watching the meter). If the meter needle moves, the meter is likely to be OK.]

Capt Ken

Thanks,
I was away from the computer all weekend. Pictures aren't coming through will check again when I get home.

The car is a '73, 350 with AC.

From looking at the wiring diagram, it isn't clear that the ammeter goes through the fuse box. Interior lights, temp guage, cig lighter, dash lights aren't working either. After I check the fuse links, I think the fuse box will be the next step in troubleshooting.

7T1vette

With all that stuff not working, it's most likely that the ground wire for the instrument cluster is not connected (broken, missing). You can test this by getting a jumper wire (10 - 14 awg) and connecting one end to a 'known-good' ground point. Then touch the other end to the metal part of the instrument panel [with key in ON position and parking lights ON]. The lights and instruments should work, if grounding is the culprit.