Burning battery light

[Turbofiat124]

1980 Spider:

This being a common thing that is mentioned from time to time.

With every circuit turned on, the battery indicator light in the tach get's brighter. This should mean that when the headlamps, wipers and heater fan are running that those circuits are pulling more power than the alternator is producing.

However I have never had a discharged battery from operating all there circuits at once for an extended period of time.

The wire that turns the light on should be the connected to the same wire that "excites the fields" going to the alternator. If I remember correctly. There is a diode somewhere in the system (perhaps built into the tachometer) that when current flows backwards (discharges) it allows the light to burn.

This leads me to wonder if the diode in the tachometer is leaking causing this to happen and an easy fix is to just wire in a second diode in line going to the tach.

Or in fact the three circuits that pull the most power (headlights, heater fan and wipers) are truely pulling more current than the alternator is producing.

If so then why am I not having any electrical issues otherwise?

[azruss]

you can do a quick test by puting a voltmeter across the battery terminals when you are pulling full juice. If the alternator is not keeping pace, your meter will read in the low 12s or even lower. If you battery is staying charged, then i would expect the meter to be reading above 12v, at least.

[Turbofiat124]

you can do a quick test by puting a voltmeter across the battery terminals when you are pulling full juice. If the alternator is not keeping pace, your meter will read in the low 12s or even lower. If you battery is staying charged, then i would expect the meter to be reading above 12v, at least.

I've got a voltmeter in the dash connected to the ignition switch. It will drop depending upon how many circuits I have. It will even move back and fourth if the signal lights are flashing.

It's a VDO from a Volvo and reads from 10 to 16 volts but no numbers in between. But there is a red zone from 10 volts to probably 12 or 13 volts, I'm assuming. I've never seen it go that low with the headlamps, wipers and heater fan all going at once.