Volt Gauge reads Low

Author Message   Tom Gruenauer Member Username: luckyenough Post Number: 15 Registered: 05-2009 Posted on Friday, September 11, 2009 - 09:16 am:    1989 351 PCM. Voltage at battery 12.66 turn key on, gauge on dash reads 11.5 V Start engine volatge at battery 13.5 on dash gauge is 12.5 V. With key on I removed the pink ign wire from the volt gauge and the gauge read correctly, to bad the engine won't start. I ran a seperate 10 G ground wire from battery to the dash no help. Does the altenator have a voltage draw? I even disconnected the electric choke, still reads low?   makomark Senior Member Username: makomark Post Number: 1436 Registered: 09-2008 Posted on Friday, September 11, 2009 - 02:32 pm:    Dash gauges are pretty well known for not being highly accurate. You can isolate the root of the issue by removing the gauge and testing the gauge at the battery directly. Having a noticable voltage drop on a key switch that's seen several seasons is also pretty common. If you have a long set of decent test leads with a digital meter, you can probe both + & - paths looking for voltage drops. Regarding the alternator, current is drawn, not voltage. The field excitation point requires current to "turn on" the alternator. Usually less than 10 amps but varies with load the alternator sees.   Tom Gruenauer Member Username: luckyenough Post Number: 16 Registered: 05-2009 Posted on Friday, September 11, 2009 - 02:53 pm:    I'm sure the gauge is ok (test with pink ign wire off reads battery Voltage) I wil test voltage in and out of the key switch(20 years old) looking for drop. Also to the same with the kill switch. Thank you for you help.   makomark Senior Member Username: makomark Post Number: 1443 Registered: 09-2008 Posted on Friday, September 11, 2009 - 03:35 pm:    make sure the jumper from the gauge to the new ground wire is good (no voltage drop) too. Checking the kill switch would be prudent, too. Most manufacturers will specify less than 0.1VDC drop across a connection, assuming adequate wire sizing for the load. For gauge wires, it should be much less. If the switch has more than 0.1V drop, I'd be inclined to change it.

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