Bulb failure warning light - Fiat Ducato 2010....SOLVED!

[namwaldog]

I have had a niggling problem for a couple of months with the Bulb failure warning light on our 2010 Fiat Ducato based MH.

I have repeatedly checked all the lights were working but the warning light persisted.

This morning I thought I would have another look at the lights and because the back of the MH was in the shade, I noticed that the N/S brake light, although working, was not as bright as the O/S.

Took the light cluster cover off, removed the brake light bulb, noted the type of bulb, found a new like for like replacement in my stache and noticed the original bulb was a little darker...

Then I thought, why does a brake light bulb need a double filament?

Removed the O/S light cluster, checked the brake light bulb and found that it was a single filament/single contact bulb. Found a new identical single filament bulb in my stache, fitted it to the N/S, restarted engine and lo & behold, warning light was off!

In my 4 yrs of ownership I have never been inside either of the light clusters so I can't have put the wrong bulb in!
The warning light has only been on for a couple of months so what has caused it to come on I have no idea?

A couple of things I have learned .....

Don't just look for a bulb that doesn't work.... consider the brightness!

When troubleshooting this problem, restart the engine after each change/modification as the warning light didn't go out until the engine was restarted!

 

[chaser]

It's a known fact that brake lights are one of the main reason for spurious warning lights.

 

[SpeedyDux]

When that day arrives, I am not looking forward to trying to access the fixings for the Ducato rear light cluster. PVC converters obviously haven't given this access issue much thought.

Next time you are on the dealer's stand at a show ask the salesman to demonstrate replacing a brake light bulb ...

 

[pappajohn]

I can't imagine how a single center contact bulb holder can accept a twin contact bulb.
Plus a stop/tail bulb has offset side pins whereas a single contact has equally spaced pins.
The bulb must have been forced into the holder enough to overcome the pins and contact both contact points

 

[namwaldog]

I can't imagine how a single center contact bulb holder can accept a twin contact bulb.
Plus a stop/tail bulb has offset side pins whereas a single contact has equally spaced pins.
The bulb must have been forced into the holder enough to overcome the pins and contact both contact points

That was my thought too!

I can only think that the double contact/offset pin bulb had been wedged in somehow.

Looking at the bulbholder with a magnifying glass reveals some extra scratches in a position where the offset pin would have connected. I have binned the offending bulb so cannot see if the offset pin has been altered.

Perhaps whoever fitted it had adjusted the bulb pins for some reason, but one thing I can confirm is that only one filament of the twin filament bulbs was lit.

The twin filament bulb I replaced (and now binned) was the one on the right of the picture above. There is only one of the offset pins showing so the mystery remains?

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[pappajohn]

It is possible one of the pins could have been removed, or missed during manufacture, to make it fit but held with just one pin.
I have had a new bulb like that.

Gets even more confusing when Volvo rear lights have an offset pin circumferally around the base rather than the usual along the base aspect.
That had me stumped for a few minutes until I looked at the old bulb....never seen that before.