Ok here we go... I bought my 1990 IROC almost a year ago, and it's completely stock. The. Volt meter pegs out in the red zone at 18 volts, and it will move back and forth when the blinkers are being used. What's is causing my voltage to be this high. I never really cared before, but I'm gonna start running out of town a lot and do not want to get stranded. And yes it's been running like this the whole year I'm been driving it, and it's my everyday driver. Bad stock volt gauge? I would I test the alternator?

 

Get a volt meter a measure across the battery while it is running and see if it really is 18 volts. If the volt meter reads 14 then the gauge is bad. If it truly is 18v then the alternator is bad. If you leave it that way many bad things can happen.

 

So I put it the voltmeter leads on the negative and positive on the battery.

 

I just did this, voltmeter showed 25.5!!! Is this even possible?

 

I've never seen a car go that high, but you better stop driving it until you can replace the alternator. Peak operational voltage for car electronics is somewhere around 14-16 volts I think? Correct me if I'm wrong, but, even if I am, that's an absurd amount of voltage

 

Change your alternator. The internal regulator is most likely shot of it it doing that. I'm truly surprised you haven't fried every electronic in the car. I'm sure you headlights are very bright at that voltage! And our right most 12v systems peak out at 16V.

 

So is any wiring of the car out of the question? So this is a inside the alternator deal?

 

Correct. Since around 73 all GM delco alternators are internally regulated.

 

if the voltmeter you used to check battery voltage is a
battery operated"multimeter"make sure the battery is
not weak in the multimeter-many of those give false
reading if battery weak...An actual 25.5 volts should
have boiled the battery dry,burnt out any light bulbs
that were on,burnt out the fuel pump,and fried most
electronics...Bulbs ,motors,electronics will withstand
18v for a while.

 

Glad you said that, checked my voltmeter a small icon of a battery is on the screen. I'll replace and see what's going on then. I figured that 25 volts was a far fetched. While I'm here, let me ask... I have never messed with a sepertine belt, I was in the process of removing my alternator. The pulley on the belt tensioner is what you push forward with a wrench to remove belt correct? Well, the bolt you grip on to, to do this is just coming unscrewed. What's up with this?

 

Ok here is an update. Finally got the alternator off, took to autozone they said it was a good alternator. Wrenched up the alternator again, started my car, volt gauge was at 13 or 14 volts! Went to close the hood, notice I didn't plug up the 2 wires in male lead to the connection on the alternator, when I plug male end up, the voltage jumps back to 18 volts! So what's up with those 2 wires?

 

actually sounds like everything might be ok except
instrument panel voltmeter might be reading a little
high-with the wires off the alternator,the alternator was
not putting out any voltage and gauge was showing
battery voltage;normally 12.5-13v,once you reconnected
the wires to the alternator it was working again.
If you measure over 15v at the battery with a known
accurate voltmeter,your alternator is putting out too
much voltage.