1967 Firebird charging gauge
 

My 67 Firebird has not had the gauges properly hooked up in many years. The printed circuit board has been removed and the individual lights/gauges have been wired individually. My question now, I am rewiring the whole car with a kit from Painless .. this is not a restoration type build, it's a street strip build, more strip. But was wondering how to wire the Gen Gauge. 2 post on the back. Is it Positive and negative? I hooked up a jumper just to test and it sparks pretty good and the needle goes al the way to charge just using a 12v battery. The screw driver in the 2nd pic indicates the 2 post associated with the Gen Gauge
Thanks for the help.

Real ammeters (I think this is one, but I can't find a '67 Firebird wiring diagram online) require a shunt. The shunt attaches to the two posts on the back of the meter and passes MOST of the current. The meter movement itself passes a slight amount of current, much less than 1 amp, usually in the milliamp range. Because of the small size of the posts on the back of your meter I'm guessing that the shunt is external to your ammeter and buried somewhere under the dash or even under the hood.

Neither of the 2 posts on the back of the ammeter should be connected to ground.

Maybe someone on the forum has a 67 Firebird wiring diagram that they could add to this thread.

I have a copy of the wiring diagrams, I followed the wires and don't see any indication of a shunt. But maybe I didn't read it right. Looking at the circuit sheet, there is a common wire for the oil press, water temp and charging gauges. I assume that would be the power side. Doesn't the ground wires run through the water and oil sending units? Looking at the pic, the yellow arrows are the water temp, orange is the oil press, and green is the charging gauge.

Wiring diagrams...Also, it's the ground that runs to the fuel tank sending unit too right?

The diagrams are likely for a '69 , not a '67. Saying that because of the file names of the two diagrams, 69wir1.jpg and 69wir2.jpg. Also, these diagrams do not show an ammeter. They do show a "gen" or "alt" idiot light.

Good point, I have never noticed that about the file name being "69". And the light instead of gauge makes sense. Now I'm wondering if the circuit sheet is intended for a charging light as well

In the Chevy trucks of the era, the shunt duty was handled in the factory harness by running a 12 gauge wire straight from the main charging junction direct to the battery 12 volt junction (red in the attached link) and an 18 gauge wire that was essentially the same but additionally routed through the ammeter (charging gauge, black/white at the main charging junction and black at the battery 12 volt junction in the attached link). The gauge is protected by a 1 amp inline fuse right at those junctions. The shunt effect is handled by virtue of the differing wire sizes.

I'd be willing to bet your factory wiring was extremely similar if not exactly the same.

Ammeters do not have any real internal resistance, so if you hook a battery directly across the posts it's basically a dead short to ground. Hopefully you didn't fry the gauge when you tested it.

https://farm4.static.flickr.com/3645...c2a8064d_o.jpg

The optional rally gauges in both 1967 and 1968 Firebirds are wired based on the way that chevrolet (Camaro) did their car's underhood wiring. Your amp gauge is a full flow gauge in that one side of it is wired to the "+" terminal of the car's battery and the other post is wired to the 12 volt output lug on that back of the alternator. Every bit of current that the car uses flows thru that gauge. There is no shunt as on other Pontiac 1967 and 1968 amp gauges (the full size cars). The problem is the wiring for the 67 & 68 Firebird amp gauge runs thru the printed circuit. The copper pathways are thinner on the aftermarket reproduction (new) printed circuit boards as would have been on the original GM made board. As the cost of copper has gone way up since the late 1960s.

Thanks for the answers guys. Looks like I will pass on hooking up the ammeter. But am I right about the other gauges? It's the negative side that runs to the senders?

In general, yes. 12v will attach to the + terminal, ground will be supplied by the mounting for the gauge and the - terminal on the gauge will attach to the sending unit.