Why is my volatage so high?

[UR2H]

I just finished installing my new Auto Meter gauges (speedometer, tachometer, water temp, voltmeter, fuel and oil pressure). On my initial start up I noticed my voltage got really high, up around 17 volts. After it warmed up a bit it dropped down to 14/15 volts. I took my car for a spin and the volts got up to 18 volts maybe even over 18 as 18 volts is the max read. Even reads that high with the lights on. At idle it sits around 12/ 13 volts. I remember replacing the voltage regulator awhile back when I replaced the alternator. Maybe 3 or 4 years ago. Car is a completely stock 77 280z besides the upgraded exhaust system. No other electrical components upgrades are running through the system except for a alarm. Don't even have the radio hooked up, not even speakers. The previous voltmeter was faulty so I don't know if it was running this high prior to the install but the car was practically a daily driver for the past 2/3 years without problems...nothing electrical anyways. What gives? All my other gauges seem to be running fine. Can anyone point me in the correct direction in trying to figure this out?

[beermanpete]

High voltage can only be caused by a bad voltage regulator (or a wiring fault in external regulator systems).

If the new voltmeter is in question check the voltage at the battery with a known good meter and compare the reading to the Autometer gauge.

[SteveJ]

There are several possible issues:

1. The gauge is not accurate. Measure with a multimeter at the battery.

2. Bad voltage regulator

3. You got the wrong ammeter and installed one that is internally regulated.

[240260280z]

Hmmm I recall writing about an L signal that went through one of the gauges and was part of the reference signal for an alterntor to sense and lock to. 1 sec.

[SteveJ]

Hmmm I recall writing about an L signal that went through one of the gauges and was part of the reference signal for an alterntor to sense and lock to. 1 sec.

Dang, I forgot about loss of sensing.

[240260280z]

Check the yellow "S" (sense) wire and all connections between the battery and the alternator. This wire is what locks your alternator's voltage. Any poor contacts or lose parts or higher resistance fusible links/crimp connections will cause it to work incorrectly.

The "L" (Lamp) wire I mentioned above is for initial excitation of windings in alternator when cranking. It does go through the battery warning light in the Voltage Gauge but it should not be an issue. I think I remember chasing it an putting a diode in it for a friends 260z that would not turn off in a past life... so long ago.

Edited July 28, 2011 by Blue

[FastWoman]

^^^ What they said!

I'll only add one thing, in case it's not obvious: Running with that high a voltage can burn out the various components in your car. If my running voltage were 18V, I'd leave the car parked until I could fix the problem.

[UR2H]

^^^ What they said!

I'll only add one thing, in case it's not obvious: Running with that high a voltage can burn out the various components in your car. If my running voltage were 18V, I'd leave the car parked until I could fix the problem.

Yeah its sitting, I'm definitely not driving it until I figure this out. But the thing is I have been using the car as a daily driver for the past 2 to 3 years and I haven't had any issues...that I know of anyways. I'm sure had I been driving around with 17 to 18 volts even for the past month or so I would have seen something fail right, let alone the last 2 to 3 years? Maybe my install is wrong?

So I feel my speedometer and tach is fine. Both seem to work and I hooked up these gauges to their respective harnesses.

So that leaves my the oil pressure, water temp, fuel and voltmeter.

Here's what I did...

Each of these gauges has a post to wire up for a ground, ignition switch and to the sender. Each gauge also needs to be wired for power to the lights.

I have each gauge individually grounded to the car.

The oil pressure and water temp are hooked up directly wired to the oil pressure sender and water temp sender.

I wired the fuel gauge from the sending unit wire in the harness.

I'm confident I did these fine.

The clock harness from the ladle didn't have an ignition switch, neither did the voltage harness. I only found an ignition switch on the oil/temp and fuel harness so I wired up two auto meters per one ignition switch. I'm wondering if this may be causing my high voltage. Thing is I didn't know where else I could've wired the ignition switches?

I'll have to buy a multimeter and check the voltage at the battery to rule out a faulty gauge.

Edited July 28, 2011 by UR2H

[Darrel]

continuous high voltage will also overcharge the battery and run it dry if a wet cell.

Check voltage at idle and at high rpm.

[UR2H]

I checked my voltage using a multimeter at the battery and it reads the same as the voltmeter gauge. I also checked all my connections via Blue's advice and everything checks out okay, no corrosion or loose ends.

Edited July 29, 2011 by UR2H

[SteveJ]

So, this is the tricky part. You need to figure out if you have a bad voltage regulator or if you have an internally regulated alternator and didn't know it. If you can rig up jumpers like the tech tip for converting to an internally regulated alternator, that can give you a quick answer. You can find details in Blue's tech tips. (Does anybody else find it ironic that Phil/Blue doesn't have a signature link to the tech tips collection? )

If the voltage behaves with the jumpers, you know that's the issue. If not, you can start suspecting the voltage regulator.

Don't forget to review the FSM for more info on diagnosing this circuit. Look in the EE section.

[Zed Head]

You should find the yellow S wire as Blue suggested and see if it also reads battery voltage. If it doesn't see the loads on the system including the battery, the alternator will just crank out as much voltage as it can. If you still have the external regulator I think that you can just unplug it and measure from the yellow wire connection in the plug to ground. If you have an internally regulated, you'll need to measure at the "T" plug.

And as FastWoman suggested, the over-voltage might damage some components. I am fairly certain that my alternator took out my ignition module when it went bad.