Re: 91 spider gauges inaccurate

[Scott Fisher <sfisher71@domain.elided>]

Tony,

Diagnostic question for you: do the gauge needles
change their position when you turn the headlights on
and off?

I had a strange symptom on my '67 GT Junior: when I
turned on the headlights, I thought my car got hotter.
 Then I noticed that my oil pressure went up AND I had
more gas.  Turning the lights off made the gauges drop
back.

It's been 5 or 6 years, but I seem to recall that the
dash lights on the Junior were grounded in series --
that is, light in gauge A had + from the fuseblock and
its - went to the + of the light for gauge B, whose -
went to the + of the light for gauge C, etc., till the
last gauge light went to the firewall.  When that
screw came loose, the lights grounded through the
gauge bodies, causing them to read high when the
lights were on.  My suspicion is that something like
this may be going on; check the wiring diagram for
your '91 Spider and see if there's a common ground for
the gauges (they're in a non-conductive plastic panel
on the '91, yes?), and then look to see whether
there's a good connection at that ground.

BTW -- my after-the-fact speculation on why Alfa has
such... interesting ground configurations (A grounds
to B grounds to C grounds to D grounds to the chassis,
rather than A, B, C and D each grounding individually
to the chassis) is that since time immemorial, Alfa
chassis have been sent to coachbuilders, who would use
a range of materials, some more conductive than
others, for the bodywork.  I'm thinking in particular
of the Superleggera style of bodywork used by Touring,
in which a (usually) aluminum body was supported on a
framework of steel tubes, with small folded linen pads
separating the two different metals to avoid
electrolysis.  Obviously, under such an arrangement,
sticking a screw into the rear fender would not
guarantee a good ground path back to the battery, so
Alfas were engineered with the grounds in series so
that the final ground could be placed where they would
effectively close the circuit.

At least that's the only explanation I've come up with
for why, when a brake-light ground goes out, the
windshield wipers stop working...

--Scott Fisher
  Tualatin, Oregon

--- Wiskas42@domain.elided wrote:
> Hello Digesters,
> The volt,fuel,oil pressure and Temp gauges on my
> Spider are not accurate, Is 
> this common? I checked the voltage at the battery
> when the car is running, I 
> got 14 volts. The dash gauge reads 13 volts. I
> filled the tank with gas and 
> the fuel gauge reads 3/4 full? The temperature gauge
> reads 156 and the heat 
> blows hot and the cooling fans come on? Oil pressure
> is 45 when cruising down 
> the road. Any idea's? Bad ground bad gauges?
> Thanks, Tony
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