Temp and fuel gauge go up when lights turned on

[rjkoop]

Anyone ever seen this before? Here's a video...

https://youtu.be/iyctOxmaGGA

Everything was fine a few days ago. No changes to electrical system or car. Any idea what could cause this to happen?

Richard

[vandor]

The ground for the gauges is weak. I ran an extra ground wire to the gauges and that stopped it.

[spider2081]

Agree with the bad ground. I think the wire diagram for the dash lights is deceiving in that it shows a white /black wire as the gauge's light ground. I believe the light bulb actually makes its ground connection to the instruments metal case. The metal case of the instrument is also the grounding point for the instrument itself and the whit/black wire is connected to the metal case. This makes the light ground and the instruments ground a common wire. If that wire is not 100% grounded power to the light will affect the instruments accuracy.

[rjkoop]

So I took apart the dash and wasn't able exactly where the instrument ground is on my '81. I guess each gauge has a white/black wire that goes into the harness and is grounded somewhere? Wasn't sure what I needed to add where. Tried cleaning the connectors (sanding and electrical cleaner) on the fuel gauge just in case and no better. Here's a few pics.

Fuel gauge


Fuel gauge connection


Middle of instrument cluster


Right of instrument cluster

[vandor]

It does not matter where they ground. Just tie into the ground wire somewhere (I think the white/black wire) and run an extra wire to ground.

[davery]

It does not matter where they ground. Just tie into the ground wire somewhere (I think the white/black wire) and run an extra wire to ground.

It seems my go to ground under the dash is the heater fan ground which is to the left of the center console.

[rjkoop]

Yep. I just wanted to check the existing ground point 1st to ensure it's clean before adding a new ground.

[rjkoop]

A few more basic questions...

And if I add a new ground do I just strip an existing ground wire (ex. from the fuel gauge wiring connector), solder in a new ground and then connect it somewhere to the body behind the instrument cluster? Also what gauge wire should I use?

Richard

[rjkoop]

Turned out I didn't need an extra ground. Once I found the grounds (to the right of the steering column just under the dash) I cleaned them and problem solved.

Richard

[spider2081]

Good news on your repair.
There is a Fiat publication " Spider 2000 Electrical Diagnostic Manual 1980-1981" available on line that I find very helpful. I tells you the general area of all the connectors and the location of all the grounds.

[Fiatlanta]

Good news on your repair.
There is a Fiat publication " Spider 2000 Electrical Diagnostic Manual 1980-1981" available on line that I find very helpful. I tells you the general area of all the connectors and the location of all the grounds.

Is there one available for a 79? I don't have any electrical issues yet, but it would be nice to have that resource if/when it happens.