360 Spider - Dipped Beam Short

Hi all,

I recently discovered an issue with my 360. The rear right outer tail light won't turn on. The running tail light wont work, but the turn signals do. I replaced the bulbs anyway - no change.

I then checked the fuse in the frunk and found it blown. Replaced fuse, turned on lights, no change. Checked fuse again and it was blown.

I replaced the fuse again, and this time, I unplugged the right tail lights beforehand (at connector 12L below). Fuse blew again. I also disconnected the bulb in the front left corner (apparently there is a small bulb in the front left headlight on the same circuit) Fuse still blowing.

This led me to believe there was a short between the fuse box and the rear tail light connector. I studied the wiring diagrams, and eventually found that if I disconnect a connector behind the passenger seat, the fuse will no longer blow when I turn on the lights (see connector 13G below.)

Cool. So I know that there must be a short between this connector and the rear tail lights. The issue now is that I can't see a whole lot of this harness. I removed the cover on the right side of the engine bay. As much as I can see of that harness looks okay. The area I suspect the short to be is highlighted in red below:

Now, I need to find a way to inspect the rest of the harness. Does anybody know how I can get a better view of it? I tried removing the wheel liner - there's no wires behind it. Maybe I'll have to go in through the cabin hole for the timing belts?

If I can't find where the short is, how can I fix this?

This is my first time doing electrical work like this, and want to know if my logic is right with this. Thank you for the help!

 

Yes, your logic is fine. You only missed one step. Disconnecting connector 40L to see if the short is in the lampholder for the right hand rectangular side marker light.

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Bulb shorts are not so common, but it's worth trying to remove the bulb. The Owners Manual suggests seeing a Ferrari dealer rather than changing that bulb yourself, so I would proceed with caution. Looking at online pics, the lamp may be removed from the rear. The lens may be glued in place?

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Unfortunately, generally, shorts to earth are be difficult to find. I don't know if wire trackers* work with short circuits unless the wire has broken completely and only one end of the break is touching earth. i.e. testing the wire from the non-shorted end. Even if the tracker did work, you still have the problem of getting access to the harness.

Is there a rubber grommet on the hole where the harness goes through the firewall? If grommets are displaced, the wires can rub on the metal. As far as you know, are there no other systems affected?

You would think that a harness hidden so well would not have issues from accidental damage. Have you had any work done on anything else recently?

*Wire trackers:

https://www.amazon.com.au/Tracker-Network-Ethernet-Collation-Telephone/dp/B06Y5K1W2B

 

P.S. Just wondering why you called this topic "dipped beam"? Dipped beam refers to headlights. Your lighting problem is a "side marker/parking/position" lighting problem.

 

Yeah I thought that was strange too, but the workshop manual refers to the blown fuse #24 as LH front and RH rear dipped beam. The bulbs that are affected are the tiny orange light in the front left headlight (all other bulbs in the headlight are working fine) and the running taillights in the rear right outer tail light.
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Now that you mention it, I recall being confused by this before. It looks like the WSM has improperly translated the original Italian “luci positione” (which Google translates as “position lights”)

 

Manual translations are generally done by language school students (they work cheap) I pretty routinely go to the italian for better accuracy.

The good news is the book shows the cable routing but converting 2d to 3d can present challenges. Harness routing and pinching is fairly common on 360. Disconnect every connector on that circuit and go from there. Try to find which section of harness short resides and go from there. No other real short cuts. Having an ohm meter connected to wire and a second set of hands reading meter while you shake, pull or wiggle harness at various places can be a help.

 

In the absence of a second pair of hands, your multimeter may have buzzer function (on the resistance setting). Keep wiggling the accessible wires until the annoying noise goes away. Of course, you'll still have the access problem. Usually the harness runs above the wheel arches, but if you've already removed the liners and found nothing, I don't know where the harness runs.

As Brian says, isolate as much as you can (including the section I mentioned).

 

From the looks of it, the only way to reach the part of the harness that I suspect the short to be is through the bottom of the car. It’s possible that it’s accessible through underneath the storage compartment for the convertible top too. I’ll see how easy it is to get in through there, but I may end up having to lift it and remove the panel underneath today.


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Ugh...

How accessible is the wiring for the rectangular side light? I have heard of damaged wiring in the rear quarter.

 

Turns out that little rectangular side marker had a wire that got pinched somewhere along the line. I repaired the wire and everything works now.

That little side marker wire is easily accessible when you remove the wheel and remove the rear small fender line panel. Thanks for the help!

 

Excellent! Thanks for the feedback.

 

New guy here, just wanted to say I appreciate this thread. I am having near enough identical issue on a 2000 360 Modena. I'll be doing some more diving with this information. Thanks a bunch!

 

This thread was a great lead to help solve my issue. Turns out it was a misconnection and mis-matched fuses(?) The workshop manual shows 21 / 24 having 5 AMP fuses, I found one 10AMP and a 5AMP, I swapped them and the lights work with a 10AMP fuse. Is that correct? Or is it just a case of mismatched amps throwing the car in a tizz and I should just match both with 5 AMPs? I will try out both combos and report back. Oh... and now I notice the LH Light in the RH headlight assembly is dead... ugh!

 

As per the diagram in post #24, fuse 21 should be 7.5, fuse 24 should be 5 amps.

These two fuses have different functions. Did you mean 21 and 24?

What kind of light? Sidelight, turn or low/high beam headlight?

 

Oppsie - I meant 23 and 24, both should be 5 AMP, however the errant light came on when I swapped a 10AMP in. I am wondering if mixing the amperage would cause such an issue.

As far as the light in the headlight assembly, I mean the sidelight I guess. The small one at the top.

 

I doubt it. Just coincidence.

So your front, side (rectangular) light is ok... and your LEFT HAND rear sidelights?

 

With regards to the tail lights and fuses, it's just weird they came on when I plugged in the 10AMP fuse. I'll replace both, and test 10AMP and 5 AMP fuses and see what happens.

The Right Rectangular light works, the Left one doesn't. The other one I am describing (and probably badly) is the parking light inside the headlight housing. The teeny one at the top

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Yes, it's hard to find a common term that everyone understands. This light can be referred to a marker light, a sidelight (non-rectangular), a parking light and, for some unknown reason, Ferrari refers to these as dipped beams (which sounds too much like headlight low beam).

Sounds like your light problems are multiplying as we speak

 

Shhh! Retract your jinx! LOL! Ferraris are very, very Italian