Re: [AMC-list] No more math before starting the car!

[Glen Hoag <hoag@xxxxxx>]

Dash illumination (including the speedometer) goes through the dash 
dimmer rheostat on the headlight switch.  I have replaced a headlight 
switch due to the rheostat being defective.  I don't remember whether 
it was a worn wiper or a broken resistance wire.  Either will cause 
the dash illumination to fail.

Here's a rough guide to how the circuit runs:

Battery+ >------ Red ------< <----Fuse block (dome fuse)----> >------ 
Red/trace ------< <--B2--Headlamp switch--I--> (continues below)

>----- Orange -----< <----Instrument cluster----> >----Ground 
through mounting screws to body

I'm *fairly* certain that the dash illumination goes through the dome 
fuse, but not positive.  It makes sense, because the headlamps run 
through a separate circuit on the headlamp switch that has a 20A 
circuit breaker.

There's a separate orange wire under the dash that connects to the 
radio (if equipped) so that the radio dial will dim with the 
instrument cluster.  That might be a convenient spot to do a voltage 
test.  If you don't get 12v there with the headlights on and the 
dimmer knob fully CCW, there is a problem in the headlamp switch (or 
the fuse, which you already know is good because the dome light 
works).  This is a pretty common switch; it fits basically all AMC 
1963-1981 and a ton of Mopar applications.  AutoZone sells it as 
Duralast SW151 for $13.99.

Note that a bad ground will also cause the dash illumination to fail.

--Glen


At 07:22 PM 5/23/2009, Bruce Griffis <bruce.griffis@xxxxxxxxx> wrote:
> I should have stated what works and what doesn't. Oil Pressure and
> Alternator lights work. High beam indicator works. Turn signals work.
> Dome light works. The dash light for the speedometer doesn't work. I
> replaced one light for dash illumination - but there may be more than
> one? I need to read the TSM again. Not sure if one fuse works for just
> the dash illumination. Time to ponder the wiring diagram again.
>
> But most lights work just fine. Just the dash illumination doesn't
> (and the back up lights, but I'll think about that later).
> _______________________________________________
> AMC-list mailing list
> AMC-list@xxxxxxxxxxxx
> http://list.amc-list.com/listinfo.cgi/amc-list-amc-list.com

_______________________________________________
AMC-list mailing list
AMC-list@xxxxxxxxxxxx
http://list.amc-list.com/listinfo.cgi/amc-list-amc-list.com