Tach

When I took delivery of my 1986 Prugna coupe just about every light on the console lighted up. Including brake failure, check engine etc. But the car was running fine. I did a lot of good braking, and just ignored the rest. Eight thousand miles later none of the lights come on most of the time, and some of the lights come on some of the time.

I have an unorthodox philosophy. If the car starts, runs, shifts and stops just fine I keep starting it, running it, shifting it and stopping it. It has worked for me the last 8,000 miles bit thats just me. But I am entirely sympatico with the anxiety of such things.

As for underdash sounds I have lost track of mine. One was a defunct anti theft device from a previous owner. Some clickings from the right side seem to be heater solinoids. From time to time, especially after a car wash, one of the auxilliary belts screams at me for short periods. But you have come to the right spot but I am not the right person. We have all sorts or experienced guys who might have advice. I suggest you consider their advice. If all else fails just drive the car.

PS: I thing I have read someplace a bad alternator diode can lead to under dash noise. One possibility is that could run down your battery when parked. Mine always ran down after a few days because of the defunct anti theft device. Until I actually figured it out when changing out the battery I just turned the battery off every day.

 

I saw this happen on a mondial i recently inspected.


For example, if i held the revs at 2500rpm, the tacho needle would bounce up and down freely, but engine made no changes in engine speed, so it appears to be the actual tacho needle contraption itself?

 

Could be a possible grounding problem? If possible check thru the circuit wiring paying particular attention to the ground/return paths and connections.

 

Elecrical problems can be irritating. For instance, when replacing my clutch master cylinder I broke the brake light switch. Itsy bitsy springs and other parts flew in all directions. The replacement I got from Ebay only had two wire connectors whereas the broken one had four.

The two wire version turned on the brake lights just fine. And if I recall correctly I did some ohm meter tests on the other two wires and I think I simply used one piece of the old four wire version to simply wire them together.

Somehow or other mixing both brake and turn signal lights lets you know if a tail light is out. I think the indication of such a situation is the turn signal will go on but not blink. I now have a four pole switch not installed, but everything is working last time I checked out back.

I am actually affraid to use the new switch because I do not clearly know which of the four wires goes to which of the four terminals. I worry if I get it wrong something else will blow. I can live with two separate systems.

 

If all of these things happened at the same time, I would follow 308mon's advice. I'll add that a faulty ground can create a lot of strange problems as sometimes circuits that lose their direct ground connection will obtain poor grounding through other circuits.

Do you have a copy of the wiring diagrams for your car? You can then look through those, starting with the affected pieces, and see what they have in common. They might share connectors or ground points. If you don't have the wiring diagrams, a search on F-chat should turn up the place where a pdf can be had.

A far less satisfactory approach might be to remove and reinsert connectors, tighten ground screws, and so forth in the hope of just happening upon the problem.

 

I just took a look at the Mondial QV and Mondial 3.2 wiring diagrams as I was curious. Odd thing is that the QV diagram show the switch with four connections, while this has been reduced to a simple spst switch in the 3.2 diagram. Maybe yours was a transitional car? (We saw all sorts of strange stuff at Mondipalooza with the cars that were made during a model change.) Anyway, It's item 28 in Figure 7 of the QV wiring diagrams and item 28 in figure 10 of the 3.2 version. I didn't try to go through it in any detail, but it's all there if you need it.

 

On my QV it was due to a faulty flywheel sensor.

 

But it will not permit the check control ecu to detect a broken stop light bulb.

That is incorrect. With ignition on:

1) The non-depressed brake pedal switch connects the green wire (from fuse 24) to the red/black wire and feeds 12V to the check control ecu. It knows the brake lights are not in use when it receives a signal from that source.

2) The depressed pedal connects the green wire (same 12V source, fuse 24) to the stop lights via the red wire and check control ecu. The check control unit knows that the brake lights are in use as the signal from the red/black wire is 0. It will measure the current in the red wire and in case of a lower value than necessary to power the 4 bulbs it will light up the "STOP LIGHTS" warning light on the check control display.

The turn signal is not be on when you press the brake pedal.

So, to wire up your 4-pole switch:

green and red/black wires are connected when the pedal is up
green and red wires are connected then the pedal is down.

And both green ends are interchangeable as they are just split from fuse 24.

 

The Tach might just be bad too (that was my case) - I took it to Palo Alto Speedometer and they verified - fixed it for like $200 - works perfectly now.

 

Paul, do you know what caused the issue in your tach?

 

Wife's Mondial T Tach jumps around at idle only when the lights are on. We have had it 9 years and it has done it since we owned it.

 

Hi Robert,

I believe it was a fried circuit or something like that.

They are fantastic - here is a post where I talk about it.

Here is a post.

Fixed Tach and Gas Gauge | Ferrari Mondial t

Basically the tach was acting like it was possessed by some demon jumping around all crazy. BTW, at idle my speedometer and tach still slightly 'bounce' but it's not a big deal to me...

Cheers