Originally Posted By: HerrStig
An oil pressure gauge or amp meter might just tell the owner something, a tach with an automatic transmission is just a decoration.
Don't tow with a truck in the mountains, do you?
A tach is useful, if you know how to use it. So are all the others you mentioned- I vastly perfer ammeters over voltmeters because they instantly tell you whether the alternator is keeping up with the electrical loads, falling behind the load causing current to be pulled from the battery and discharging it, or actively pushing charge into a battery. When I used to drive my '66 Polara (ammeter in dash) every day and occasionally had to jump-start someone else, I could hook up the jumper cables and watch my car's ammeter to tell them when their battery was getting full enough to go ahead and crank their car. I could also tell them pretty reliably if their battery was bad, because the charging current would drop MUCH quicker than if it was good but discharged.
But in practice it is harder to make an ammeter reliable. Old Mopars all have ammeters, but it means passing the entire battery current (except for the starter) through the ammeter or through a high-power / low ohm shunt resistor and through a parallel voltmeter to make an ammeter. Either method inserts losses or high-current contacts in the system which are prone to fail over time. At a car show, look how many old Mopars have the alternator and battery wires through the dashboard bulkhead bypassed because the original spade connectors eventuallly got a little corrosion, which causes half an ohm of resistance, which at a mere 10A charge current creates 50 watts of heat in the connector and melts it. Don't ask me how I know this.......
Ammeters also move around a LOT just during normal operation, so like real oil pressure gauges they tend to confuse and scare uneducated operators.
An oil pressure gauge or amp meter might just tell the owner something, a tach with an automatic transmission is just a decoration.
Don't tow with a truck in the mountains, do you?
A tach is useful, if you know how to use it. So are all the others you mentioned- I vastly perfer ammeters over voltmeters because they instantly tell you whether the alternator is keeping up with the electrical loads, falling behind the load causing current to be pulled from the battery and discharging it, or actively pushing charge into a battery. When I used to drive my '66 Polara (ammeter in dash) every day and occasionally had to jump-start someone else, I could hook up the jumper cables and watch my car's ammeter to tell them when their battery was getting full enough to go ahead and crank their car. I could also tell them pretty reliably if their battery was bad, because the charging current would drop MUCH quicker than if it was good but discharged.
But in practice it is harder to make an ammeter reliable. Old Mopars all have ammeters, but it means passing the entire battery current (except for the starter) through the ammeter or through a high-power / low ohm shunt resistor and through a parallel voltmeter to make an ammeter. Either method inserts losses or high-current contacts in the system which are prone to fail over time. At a car show, look how many old Mopars have the alternator and battery wires through the dashboard bulkhead bypassed because the original spade connectors eventuallly got a little corrosion, which causes half an ohm of resistance, which at a mere 10A charge current creates 50 watts of heat in the connector and melts it. Don't ask me how I know this.......
Ammeters also move around a LOT just during normal operation, so like real oil pressure gauges they tend to confuse and scare uneducated operators.