"How to: dash lights", finally

We suspect an issue with the ground. Below is an excerpt from the schematic. You need to increase the magnifications.

Light numbers 54, 55, and 50 are, respectively, Parking Brake warning light, High Beam warning light, and the Brake Failure warning lights..

None of these work. But they do work when I take the tachometer out and apply voltage to the connector that feeds them.

The schematic seems to indicate that these lights, along with the two back-light bulbs (indicated by empty circle with an "X" inside) share the same ground. But the schematic indicates a switch. I tried my best to follow the wires that come to the switch. One wire goes all the way to the electronic ignition system, which generates the tachometer signal..

But we are lost as to what that switch does, where it resides, and whether it is interfering with the function of the three lights that are not coming on.

Also, two of the lights (parking brake indicator and brake failure) share the same ground.

the other light (high beam indicator) has a separate ground.

So we are quite confused.


- Sam in Saratogaa




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Hey Sam,

I'm taking a quick shot, which may/may not resolve your issue. But are you sure the LED polarity isn't reversed? You can double-check by rotating the bulb 180 degrees in the housing.

 

It now sounds like a connector issue since it works on the bench. Check the pins in the male and female big white connectors . Specifically the ground wire/pins. I actually ran a separate ground from chassis to the instrument brackets.


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That is exactly the problem. The three lights I mentioned are wired in reverse. You can kind of see that by looking at the schematic, but we figured it out by following the ground wires on the tachometer. I think that is what Crowndog meant:

Wiring lights in reverse polarity is not a big deal when using incandescent bulbs. But, of course, this does not work with LEDs.

You cannot rotate the bulbs 180 degrees. They are not wedge lights, they are bayonets.

I will look online to see if I can find the proper size bayonet LED bulbs that are either polarity neutral or reverse polarity. I will keep you posted.

- Sam in Saratoga

 

Also the high beam light only works if the stalk switch is on or flashed.

 

and if we simply place convertisseur boost to increase the voltage to 15 or 16 v........?

 

I had the same problem with the screws but I remember from my tool and die days you take a round punch in this case about 4-5 mm in dia and hit the center of the flat head hard a few times this will loosen the screw then take a gods sharp Allen (grind the front flat)key and knock it all the way in that should work

 

Great info in here. I'll use it soon, thanks all.

 

There is nothing to fix to do this, you can drive with the fog or parking lights any time it is in the manual

 

I know what I'm doing this weekend to my 328.

13 years later after this post, options for LEDs are vastly greater and probably dimmable so the rheostat might remain functional.

I've already changed all exterior bulbs (sans headlamps) to LED with fantastic results.

 

https://www.aliexpress.com/item/32879133118.html?spm=a2g0s.9042311.0.0.35894c4dCm4c11

 

oops no longer available. check ''find similar parts''
They are out there and cheap

 

My rheostat is still functional in my 84.

 

https://www.ferrarichat.com/forum/threads/how-to-convert-instrument-cluster-lights-to-leds-with-factory-blue-green-tint.678683