How many are using the factory amp meter

The ammeter in our cars, and pretty much all automobiles that use an ammeter does not measure total current draw. It indicates current flowing from Alternator (charging) or from Battery (discharging). Only when the alternator is not running, would the ammeter show total current flow since the Battery is powering everything.

Automotive voltmeters are usually set up to measure the total voltage difference in the system. Whether it is charging or discharging is then assumed based on typical, or compared against actual battery voltage.

With headlights wired on the alternator side, during low alternator output a portion of the current is supplied from the battery. This goes through the ammeter's shunt. Ammeter then shows discharge. Since the alternator provides the higher voltage under almost all circumstances, Dan Stern recommends wiring headlight's to draw on the alternator side when converting to relays. Of course that wiring must fused since both the fusible link and the circuit breaker have been bypassed. I initially was concerned about the ammeter being less informative, but Dan straightened me out and I have now proved it to myself.

For those that prefer to remove or alter the ammeter and wire in a voltmeter, go for it. I agree it is has potential for failure. However, the evidence is that there are other more likely problem spots in the electric system if one is concerned about failures.

Edit: Pete's idea is a good alternative for taking one of the high current draws off of the ammeter!