bouncing gauges

Both sound like they are from a bad voltage regulator. If the ammeter needle matches your revs, the VR in the alternator is shorting to ground (or otherwise shot). The fuel gauge on *most* cars has a seperate VR from the alternator however...I have NO idea on your Ferrari...but that's the first place to look.

One other thing: do you have an electric fuel pump as an aftermarket add on? If so, it's likely connected to the coil/tach + and that can cause the tach to bounce, and maybe other dials as well. But this would not affect the ammeter I don't think.

Ken

 

I would vote for two seperate problems. I would investigate both seperately.

On the fuel gauge side I would pull the sender from the tank. It is very common for the windings on the rheostat that is connected to the float to deteriote. I had this happen on a Boxer whose fuel sending unit I replaced last year.

On the bouncing ammeter, I had this problem with a Daytona when I first purchased it. A number of people said it was typical of some cars. The gauge would swing widely about a 1/4 way to the - and then about 1/4 to the +. Drove me crazy.

I finally went through the car cleaning the majority of electrical ground connections especially for the tail lights and dash. Improved things 95%. I get a little bobble but close enough to rock steady that it doesn't bother me any more.

Hope this helps.

Drew

 

This is true; my ammeter bounces a little with the blinker but it's no big deal. That would be a bad ground more likely than not. That's why I asked if it acts like a tach with the motor. Many/most alternators hold the VR in with two insulated screws (and one that's not), and as the years go by this insulation can deteriorate and short it to ground. Fixing it can be as easy as replacing these two screws. But if it's bouncing on it's own with no rhyme or reason, check the grounds. You might also remove it and see if the inside is corroded. Mine was a nice shade of green crud when I checked. You can clean this out if replacement is an issue. Be careful though; remember you have full + battery power there so disconnect the battery first before you dig around behind the dash!

I also agree that you're looking at two seperate problems.

Ken

 

Ammeters aren't grounded, they show current flow through the circuit and not to ground. If you ground either side of an ammeter it will short the circuit directly to ground.