[DeTomaso] Temp Gauge Rise

[boyd casey]

I wrote a post in the not to distant past where I also recommended upgrading
mas many ground points as you can. I never have expierienced a car with such
a marginal ground system. In my post I mentioned that I had added a direct
ground to my starter, an additional ground strap from my ZF to the chassis .
I also mentionedthat everything in the guage panel goes to the small ground
post on the Aipillar and tht you could find an additional shorter path the
screw holes on the shift gate by removing the rectangular cover and
rattaching a 12 guage wire to a closed loop connector and placing it below
the shift gate so it is hidden from view and running the wire under the
covers to the area behind the guage panel. Another place where you can
observe immeadiate improvement is by regrounding the fan blower moter for
the heater fan. It may add to the confusion of a future owner but when I was
installing my new fuse bow and Pantera electronics headlight controller I
took a multimeter and serached for opportunities to improve many of the
poorly grounded components. It will probably add to the confusion of some
future owner who is trying to understand the already cryptic wiring and the
variance between many Panteras actual wiring and the published schematics.
But C'est le vie!
Boyd







On Tue, Apr 27, 2010 at 10:31 AM, Dave McManus <dave at damardirect.com> wrote:

> Will, I noticed the same problem last year. Here is what SOBill has to say
> about the problem: (I sent the attachment to you directly)
>
> >From 2-23-09
> Dave,
>
> 12V is applied to the temp gauge. The temp gauge divides this voltage and
> sends part of it to the temp sender in the engine. The temp sender is a
> resistor connected to chassis ground. Inside the gauge the divider circuit
> and a light bulb are both connected to a terminal on the gauge case. The
> terminal on the gauge case is connected to a like terminal on all the other
> gauge cases ("daisy chained") and eventually connected to chassis ground.
>
> When you turn on the headlight, you also turn on the lights in all the
> gauges. The current drawn by all the light bulbs in the gauges will cause
> the ground terminal on each gauge to be at a slightly higher voltage than
> the ground terminal at the sender for that gauge. This difference in
> voltage
> between the two ground points for the temperature gauge will cause the
> temperature needle to move up scale.
>
> See
> http://www.panteraplace.com/Electrical/SOBill%20Veglia%20Temp%20Fig%203.jpg
> for the details of the gauge circuitry. Just imagine that the ground
> connection on  the right hand coil in the gauge (which is the ground
> terminal on the gauge case) and the ground connection from the sensor
> (which
> is on the engine, via the ground strap at the ZF) are at different voltage
> levels. Elementary, my dear Watson.
>
> So there you have it.
>
> To solve this problem, connect a wire directly from the ground terminal on
> the temp gauge to a solid chassis ground. The factory connected the gauge
> grounds in a "daisy chain" because it was simple and easy. Each gauge
> should
> have a direct connection to ground. In fact,  the lighting circuit should
> have a separate power and ground from the sensing circuit ..... sort of
> like
> the space shuttle does it.
>
> Mike Drew suggests adding a second ground connection to the daisy chain at
> which ever gauge has a single black wire on it's ground terminal. That fix
> might work, can't hurt to try.
>
> Attached are pictures of a test I did with my temp gauge and a one ohm
> resistor.
>
> Have fun,
>
> SOBill Taylor
> sobill at aol.com
>
>
>
>
>
> -----Original Message-----
> From: Will Demelo [mailto:wdemelo at cogeco.ca]
> Sent: Tuesday, April 27, 2010 6:31 AM
> To: detomaso at realbig.com
> Subject: [DeTomaso] Temp Gauge Rise
>
> Another fellow on the PI board has reminded me of a similar problem I'm
> having. My temp gauge rises considerably ( 15-20 deg) when I raise my
> headlights. I was thinking it was induction in the wiring, but I beleive
> the
> headlight switch only carries the current of the relay coil, which is
> minimal.
> Any suggestions?
> Will
>
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