72 Swinger Harness Replacement

This exact problem is common and often has to do with the poor connection in the bulkhead connector. The IVR does not connect to the ammeter. Since I always want a mechanical Oil pressure gauge under the dash, and still want an ammeter for diagnostics, I've taken to running those wires to an aftermarket ammeter paired with my oil pressure gauge, at least then the wires are not in the bundle with everything else if something goes wrong. Then you can rig your factory ammeter in the dash to function as a voltmeter. Between the two you have an excellent finger on the pulse of your electrical system.