Technical Faulty Lights and Wiring Upgrade

[Pete145]

Hi everyone,

I, like a lot of us here in the UK, keep my car running through the winter as much as possible. However it's not often that I drive in the dark. I did so recently (for the first time in ages) and I've noticed a fault with the rear lights/brake lights.

When the lights are off, the brake lights operate as they should. No problem. However when the lights are on when I apply the brakes the rear lights seem to switch off as brake lights come on, and then return to normal when I stop braking.

I assume that this is a pretty simple issue to fix, and that the lights might just be wired up incorrectly?

Over the last few months my horn has stopped working (no obvious visual issue) and the dashboard light (it's a Lusso model prior to Abarth 595 style of conversion) has not worked since I've owned the car, despite the bulb being changed, and the interior light switch has also been missing since I've had the car.

So, a few electrical gremlins to fix before the next MoT, specifically the rear lights/brake lights and the horn.

Thinking bigger picture for a minute, when I stop and think about it the car's now 46 years old and, as far as I can tell, it still has the original wiring. I've had an alternator fitted, and I know that wiring looms can be replaced (albeit a time consuming exercise), but has anyone ever gone the whole nine yards and completely modified the electrics on a 500 with a modern, more reliable set-up (not just replacing like for like)?

 

[Ricambi Fiat 500]

Hi
After 46 years I am sure there has been a few modification with the electrical which is normal. I would suggest calling an electrician to take a look at your 500 before going to MOT. For the Horn issue it could just be that it does not receive contact with the negative. If you need a new wiring loom let me know I sell used & new spare parts. If you need anything email me [email protected]. What Model Fiat 500 do you have?

 

[the hobbler]

Morning Peter;
Had a similar problem with my 500, in that Ann told me 1 day that my rear lights (side and brake) seemed funny. It turned out to be the total crap 'pattern' modern rear lights. In the original, factory, lights the bulbs are held in place in METAL bulb holders which have proper locating slots for the bulbs. In the 'pattern' lights the bulbs are held in by luck, spit and friction. On my lights, the bulb-holding/locating parts of the rear lights were only plastic with a securing slot on only one side of the bulb holder. The bulb on one side had therefore moved to a point that the incorrect terminals were making contact. Although they don't look as smart, I have reverted to using my original 'factory' rear light units whilst my contacts in Italy try and find me another pair of originals. I looked at trying to fit original 'innards' to modern 'outers', but they don't match!!! Even the rubber light-to-body seals are slightly different. As I could see that I ran the risk of buggering up my only set of 'originals', I immediately stopped
trying that adaption. The only simple 'cure' to this problem that I can come up with is to wrap the bulb with tape so that it is a secure fit in the bulb-holder.

 

[Pete145]

Hi
What Model Fiat 500 do you have?

It's a 1971 Lusso base, which has been modified to pretty much exactly match a 595ss specification (top and bottom of engine, carb, suspension etc).

A close neighbour runs an 'auto-electrical' business. I've never used him or even spoken to him about the Fiat, but he might be a sensible first port of call.

Hobbler, interesting and useful response. I'll take a look at the rear lights and see if I may be facing similar challenges.

 

[AndrewHarvey]

the rear light units use twin filament lamps - one for tail light - one for stop light
There is no reason to loose feed to tail light when the brake is pressed.

Two screws remove the entire rear light and a multi-meter or lamp with flying leads will tell you whether your loosing feed or not......2 mins max...

 

[fiat500]

the rear light units use twin filament lamps - one for tail light - one for stop light
There is no reason to loose feed to tail light when the brake is pressed.

True that.
On my trailer, which has a terrible design of rear light unit, I have had the same problem due to a bad earth when one circuit was tracking back through the secondary filament and using it as an earth.
I have to clean up and lubricate the outside of the bulb and its socket in the lamp to improve the earth connection.
Mind you, I know what Tom means too. Ypou can even get the wrong filament illuminating in those circumstances.

 

[Bleeding Knuckles]

Hi Peter, not withstanding what everyone has said check for a good earth and positive contacts on all lights and see what resistance you get on the main feed it could indicate a bad earth.

Ian.