1987 Ferrari Mondial Coupe Gearbox question

You can top of by putting gearbox oil in this hole with plug 22 on this diagram =
https://www.eurospares.co.uk/Ferrari/Mondial/Mondial_3.2_QV_(1987)/PartDiagrams/028/Gearbox_Transmission
but first you have to remove the plug nr. 51 on this diagram =
https://www.eurospares.co.uk/Ferrari/Mondial/Mondial_3.2_QV_(1987)/PartDiagrams/029/Gearbox_-_Differential_HoUSing_and_Oil_Sump
as overflow. When enough oil in the gearbox, oil will starting coming out on the hole of plug 51.
You do not need a lift but the car has to be on horizontal level when topping of.
Please note that the control box where the light is on, cannot be trusted. These are very unreliable and essentially impossible to repair if defective.

 

The unreliability of this entire "warning" system is probably why the system was eliminated in 1988 models.
I'm not saying you might not have a problem, but to my knowledge low gear oil is a very rare occurrence unless you have a serious leak, which should be noticeable when you park the car.
Alden

 

The system with the Control Box and Electronic Unit for Check Control was assembled by an electronics engineer who is no longer with us. No one knows how it works, what the schematics are, or how to repair it. That person likely didn't pass on his information to his successors, and no one at Ferrari still knows how it works. Dealerships advise Mondial owners to disconnect the three colored connectors from the Control Box, which I did. This has no effect whatsoever on the car's operation.
This is the Electronic Unit of Check control hidden under the passenger footwell =
https://www.eurospares.co.uk/Ferrari/Mondial/Mondial_3.0_QV_(1984)/PartDiagrams/120/Electrical_Board part 22

 

To change/add to the gear oil, you need to remove the left rear wheel well to access the fill plug. The fill plug is an allen plug 12mm, so you need that type of socket. I get a funnel with a piece of 5/8 inch hose on it, and use the funnel in the engine bay area with the tube in the fill hole. You could do a quick "top it off" with a quarter of a quart, if it was actually already full this amount of overfill will be ok. But to properly fill and guage the level, you have the upper plug under the car opened, you need the car level, and it is full when the oil drips out that hole.

If the gearbox is indeed low on fluid, you probably have leaking differential seals, at the inner rear cv joints. Not usually a huge leak here, but will throw some gear oil on the exhaust headers and give you some smoke and smell so if you have that going on that is why. Or an internal shift shaft seal, where gear oil leaks into the oil sump. If your oil level is more than the high level, and the gearbox low, that would be the indicator of that problem, so give the oil level a check.

Otherwise, there is no where else the gear oil would typically leak from.

Or, and more likely, you just have a faulty warning light.