Technical Wiring Harness Replacement

[JumpJet]

Gents,

Troubleshooting some electrical gremlins (horn intermittent, brake lights and turn signals stopped working) on Martina are starting to drive me bonkers. I've been shooting wires for awhile now, but everytime I get under the bonnet, it becomes a mess. It seems that she's got a bodge job 500L-based loom with a solid mix of south-Italian wiring splices, tape jobs, connectors, etc... See pics for details.

I'm about at my wits end and seriously considering replacing her whole harness with a new one from MrFiat. I'm thinking of starting from scratch, and integrating some nice WeatherPack connectors for some of the larger portions (ie. engine bay harness & dash).

Does anyone have experience with these new, repro harnesses? Are they complete? I don't see fuse blocks on them, so I was just wondering. Can you swap them out in sections - in the diagrams and on the car I don't see any connectors between the major areas of the car, but I was trying to avoid ripping it all out at once - like I said, I'd like to section it off, but do it well. Eventually, Martina will get a complete resto, so I'd like to future-proof this too.

I'm just looking for some thoughts on the kits and my intended course of action from those with experience in this. Thanks in advance.

-Matt

 

[AndrewHarvey]

I bought the expensive version that is completely labelled - and it was the most straightforward thing. I needed to add a few extra cores for my enhancements and then I wrapped it in a coraplast wiring loom tape - it's a better solution than the fabric tape as it doesn't break down over time
Highly recommend a replacement

 

[Franko500]

Hi Matt,
Looking at your images I cant see anything really wrong in terms of the loom.
Someone has clearly fitted a hazard warning light relay into the indicator system but apart from that the white connector blocks are standard and to be honest the black tape wrapped around every 6 inches or so was also pretty standard. Well it was on my 500L when I got it and it clearly hadn't been tampered with.
If I was you I would stick with the one you got otherwise you could end up with more problems.
The wiring loom is a one piece loom. And compared with modern car looms there is not much to it.
If you can list the actual problems then later today I should be able to tell you what coloured wire go where.

 

[JumpJet]

Sean,

I have all the wiring schematics and I've been looking all over for commonality between the issues I've been having - intermittent horn, no turn signals, and now no brake lights. The horn tends to work sometimes when I mess with the jumble of wires behind the fuse block, leading me to think there's a short or loose connection in there somewhere. The brake lights are stumping me. The switch works, as with the pedal down, I've got connectivity, but current to the left rear light is intermittent (short?).

The turn signals... I have no idea. Maybe it's just a bad relay, but in my experience they usually just fail on where the light just doesn't blink.

Everything was working great when I shipped the car over here and one by one, these little gremlins have been popping up. I don't know if there's some internal corrosion thanks to the trip over or what.

It's driving me mad and I was debating getting a new harness, and splicing in Deutsch or Weatherpack connectors for the aft portion of it. I'm not too keen on trying to tackle that under bonnet disaster right now.

Thanks.

 

[Bambino]

Electrical gremlins on Italian cars are something of a running joke. I have a number of old Italian cars and over the years have sorted the electrics so that they are now reliable. One recurring problem is the earthing points, so I'd check all of them next before you ditch the whole harness.
Chris

 

[Franko500]

If everything was working fine and slowly things have stopped working then that means your wiring is correct. What you will find that causes things to stop working is poor earthing as Chris mentioned and also poor connections. The bullet connections on the wires coming from the steering column are a main culprit. These are all the wires to do with your lights, indicators & horn. Check they are all clean and connected properly.
Also fuse box connectors, the terminals on the fuse box can corrode, maybe a new fuse box or clean the terminals?

 

[fiat500]

I have found all of the above to be true. Some of the original spade connectors on mine looked OK but had lost their grip and are easily replaced.
Some of the connections, such as the ones at the horn and brake-light switch, are in a dire location if the car is used in all weathers and will quickly corrode, based on my experience.
Whether you clean up the connectors or replace the loom, use something like this to coat all contact areas at joins and switches etc.,before and after you connect them up.
http://www.shopwurthusa.com/wurthst...ease/Dielectric-Grease-3-Oz-Tube/p/0893844100

 

[JumpJet]

Fellas,
I think I've chased the light issues to a bad flasher (and possibly bad ground related to it) but, while replacing the flasher has fixed some of the light woes, it has presented another perplexing issue.

For now, swapping in a new relay got the turn signals working (outside), but the inside indicator won't work unless I switch the purple and blue/white wire on the flasher. Pictured is the config of the flasher with the outside indicators working, but the internal indicator does not work. Did I get the wrong flasher?

Now, obviously based on the wire coloring and slightly modified indicator light (positive only pin replaced with +/- wiring), this wiring has been fiddled with quite a bit since '66, but it appears I mostly have a 500L harness.

I'm not super relay savvy, so this is perplexing. :bang: Ideas?

 

[Nick Striker]

Where did you get your wiring harness? Is it for a 500 F or a 500 L?