F355 5.2 motronic Electrical problem

There should be a wiring diagram for your car available to download on this forum. It’s very hard to diagnose an electrical problem without a diagram.

 

I don't think you are explaining the problem properly. The dash does not need power (other than for background lighting and warning light power). Dash background lighting and warning light power is mostly provided by a green/white wire. There is a yellow/black wire on the ignition lock which provides ignition accessory power to the battery warning light and the ABS warning light on the dash... and to the ABS system itself via 3 amp or 10 amp fuse in the luggage compartment (Teves ABS system/Bosch ABS system respectively)

Teves diagram:

https://www.dropbox.com/t/lxoz65iH97GaCdM7

Bosch diagram:

https://www.dropbox.com/t/vipx14zhuIuG3Acz

Do you have an F1 car or a gated car?

Normal ignition power (2nd key position from OFF) goes to the fusebox on two blue wires (plugs A and C). Note that there is a wire colour change on the blue wire going to plug A (to blue/red).

The blue/red wire on plug A mostly goes straight through the fusebox (no relays) and supplies power to things like the alternator, Immobiliser and LH engine coilpack on a yellow wire ... and to the RH engine coilpack on a yellow/black wire. i.e. the fusebox has two outputs. The red/blue wire also powers some HVAC components. The blue wire on plug C goes mostly to the relays inside the fusebox.

https://www.dropbox.com/t/lxoz65iH97GaCdM7

Assuming you shorted the yellow wire coming from plug "I" on the fusebox (see diagram)... This yellow wire has no fuses! If something is not working after the short was removed, then perhaps you have melted wiring. There is a 9 pin plug near the Motronic ECU behind the passenger seat which can cause issues. Check that for signs of melting/burnt pins. Disconnect the plug and look for ignition volts on pins 2 & 3 (yellow and yellow/black wires)

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What systems are working on your car at the moment? If that plug is faulty, it shouldn't affect things like ABS. Is your ABS light illuminating when you turn the key to the first position?

 

Sorry, I got my links messed up...

Teves: https://www.dropbox.com/t/VkNfzTHcObc7rmdU

Bosch: https://www.dropbox.com/t/0Zyq7iKWjdEBXvqm

Ignition system: https://www.dropbox.com/t/NAyeCmhbASurxtUJ

 

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Correct.

Why not just pull a relay or fuse to check for ignition volts at the relay panel?

e.g. fuse 24 should have ignition power .

Or just backprobe the connector on the steering column. Look for 12 volts on the blue wire with the key on.

 

If you have no lights, look for power (with the sidelight switch on) at fuses 12, 13 and 14 in the luggage compartment.

 

Sorry, made an edit to my last message.

 

That means you have a short circuit somewhere. Are you sure it was a ground and not a low resistance (like a relay coil)?

 

Sorry, I'm not sure how you are checking the wiring. Did you find a ground on the blue wire with the battery cutoff switch OFF? I wouldn't want to be looking for resistance to ground with power on the circuit.

 

I'm just reading the wiring diagrams that I redrew in colour (because the original Ferrari ones were so bad). Also, I have had many problems with my own F355 (5.2)

I had to re analyse the circuit. I see the ignition also powers some of the immobiliser circuitry. I'm not sure what resistance to expect on the blue wire.

If you have a short on the blue wire circuit, it will be very difficult to isolate the problem. Perhaps adding a fuse is a good idea, but I don't know how you would insert it into the circuit (unless, as you suggested earlier, run battery volts to the blue wire (and insert a fuse).

Alternatively....

The blue wire powers fuse 24, relay O and relay L. It also powers engine management circuits and sends power to the immobiliser system. Perhaps you could disconnect the 9 pin plug near the ECU (to remove the engine wiring from the circuit), and pull fuse 24, then turn the battery back on. I don't think it is likely that you have a short in the immobiliser wiring. Now see if you have 12 volts at the fuseholder for fuse 24 or your lights now work.

 

Ignition power doesn't go directly to the forward luggage compartment fusebox. Only if you, for example, turn on the lights, can ignition power go to the luggage compartment relay panel. Note, however, fuse 24 does power HVAC components in the luggage compartment.

Did you check fuse 24 to see if it had blown? That powers a lot of things on the car (HVAC, instruments, etc). Also check fuse 12 in the luggage compartment. That powers instrument lights.