Piston Slap: Ground wires, brown wires in the Spider’s web?

Jeff writes:

I’m going nuts! Maybe you can help me? I’m restoring a 1977 Fiat Spider, and the brake lights, turn signals, and backup lights don’t work. Also none of the gauges work (except the speedometer). Do you have any ideas?

Sajeev answers:

Usually problems that bad (in other words, they make you go nuts) are due to the most basic of electrical issues: failing power or ground wires. So, start by cleaning and inspecting all chassis grounds (perhaps the rear lights share a common ground), and add a dab of dielectric grease at the grounding points to ensure they remain healthy.

If the problem isn’t resolved—perhaps even if it is—performing the brown wire fix is the next major weak point on these Fiats. Inspecting/replacing weathered or corroded battery cables is always a good idea, too. Lastly, while not germane to this issue, the Fiat forums suggest relieving electrical system stress via adding relays (or just buying a complete kit) to the headlight wiring harness, which also benefits light output for your evening cruises.

What if all this fails?  Get a multimeter with really long leads, and check for continuity on all affected circuits to see which one(s) failed. Getting a wiring diagram is also a good idea. But if the wiring looks brittle, exposed, cruddy, or generally unservicable, remove the whole thing and send it to someone who can rebuild it. The latter is possibly your best bet for a 1970s Fiat, especially if it’s been stored outside and exposed to the elements.

Here’s to hoping this is an easy fix. Best of luck!

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