Re: [BaadAssGremlins] Alt light

[Todd Tomason <jayscore@xxxxxxxxxxxxx>]

Dave,

I know I'm jumping in a little late on this one, but it sounds like the 
problem is most likely the 12v feed into the instrument cluster.  The 
alternator light is a very simple design that works backwards to what you 
would think.  

Under normal operation the light has 12v on one side that comes from the 
instrument cluster, and 12v on the other side that comes from the alternator.  
Since the voltage is the same on both sides there is no current flow and the 
light is off.  

Here's how the light is supposed to work.  Let's say something is wrong with 
the alternator and it's only putting out 8v.  This puts 12v on one side of 
the light and 8v on the other side.  That's a difference of 4v and current 
will flow, lighting up the light.  This also explains why the light will 
sometimes glow or flicker.  If there is a slight change in voltage then that 
small amount of current will light up the light just a bit.

But it can also go wrong from the instrument cluster side.  If you're not 
getting 12v to the instrument cluster for some reason, then you have 12v on 
one side of the light and 0v on the other side.  Current will flow and light 
up the light.  In my case it was a bad fuse holder for the instrument 
cluster.  I squeezed the holder a little tighter and put in a new fuse and 
that took care of the problem.  Since you've also lost the fuel and temp 
gauge, it sounds like you have a problem in the 12v feed to the instrument 
cluster.  It could be a bad fuse, loose wire, etc.  It's probably not the 5v 
regulator because that wouldn't affect the alternator light.

Hope this helps,

Todd

On Monday 26 September 2005 09:30, David Kaunisto wrote:
> What was once only a bright alternator light has turned into a bigger
> problem.  Now the fuel and temperature gauges don't work.  I didn't have
> time yesterday to check the fuse, but its always something.  Any other
> ideas?  And Doc, I don't have A/C in the car yet, but that's how this whole
> thing got started - I changed out the heater box for an AC/heater box with
> the intention of adding AC at some point.  So I may be a Motorola man for
> awhile.
>
> Dave
> 72 Gremlin X 304
>


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