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Fiat Ducato light fuse blowing

Keith Brown

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Hello there, I wonder if someone can give me some advice?

I own an 02 2.8 turbo diesel Swift Gazelle and am having trouble with a fuse blowing. The fuse is F6, in the glove box area, which is a 7.5A fuse and controls LH rear side light, LH rear high level light, RH Front side light and cigar lighter surround light. The fuse seems to blow when the lights are switched on and the engine gets above 3000 rpm. If lights are off, or revs are below that then fuse stays intact?

When fuse is replaced and lights switched on then all bulbs work fine, there are no failures. I have cleaned all terminals and connectors that I can and still not solved it - I have now bought every 7.5 Amp my car spares shop has!!!!

Any advice or guidance really appreciated.

Thanks a lot, Keith

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Dunno - personally, I'd try replacing the 7.5A fuse with a 10A one. I would not expect this to effect a miraculous cure, but the experiment should not be harmful and it might prove something.


Currently, all you know is that, if you switch on the vehicle's lights and rev the motor to over 3000rpm, this particular fuse WILL blow, so (unless you can guarantee not to exceed 3000rpm) there's only limited benefit in carrying lots of 7.5A fuses.


If the 10A fuse also blows (which is what one might logically anticipate) then at least you'll only have wasted a few pence and you'll have established that 'over fusing' the circuit has no effect on the problem.

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I totally agree with Derek and I was about to say the same thing yesterday when after consideration I decided against as I did not want to start another round of confrontation from the Mr Perfect branch of the forum who only do things by the book!
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One possibility could be vibration causing a chaffed wire to blow the fuse. With the engine off, and the lights switched on, have you tried moving wiring around to see if that blows the fuse. Could be anywhere, engine compartment, dashboard, chassis, lights, etc.

Brian B.

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Hi Keith,


Here are some suggestions for things to try in no particular order...

(You'll need a reasonable DVM something like this if you don't have one... Maplin DVM).


1. Measure engine battery voltage with engine running and slowly rev to over 3,000 rpm.


2. Repeat 1 with headlights, blower fan and other electrical loads turned on.


3. Measure the voltage at the fuse (with the fuse fitted - there is normally a hole in the top for this purpose) with the lights off then on and then rev the engine to over 3,000 rpm.


4. Remove one bulb at a time (from this circuit) and repeat test 3.


5. Measure the voltage across every bulb holder with the bulbs fitted and rev engine to over 3,000 rpm.


6. Get a current tester that plugs in place of the fuse(Fuse meter lead or Fuse current tester) and turn lights on and rev engine to over 3,000 rpm.


7. Remove one bulb at a time and repeat test 6.


8. Follow all visible wiring to the affected lights and disconnect and reconnect every connection then follow all earth wires to their earthing point and again remove, clean and replace every one.


9. Check engine to chassis earth. If accessible remove, clean and replace. If not use a voltmeter between battery negative and a good earth point on the engine and rev the engine over 3,000 rpm and note voltage. Anything over, say, 1 volt may signify a bad earth.


You asked for suggestions so get your teeth stuck into that lot... . :D


Post the results and we'll take it from there.



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Thanks for the extensive test schedule, which I have had a go at. The only tests I haven't done are the one's which require a fuse tester. I haven't access to one oif these, but if you hink it will help then I shall shuffle off and buy one. Right, results below:-


Test 1. Engine idling - 14.4v, engine at 3,000 - 14.29v


Test 2 Idling with lights on - 14.1v, at 3,000 with lights, radio, blower etc - 14.1v.


Test 3 Voltage at fuse - Idling no lights 0.03v, lights on, idling 13.62v, at 3,000 reached 13.62v then blew so might have gone higher?


Test 4 High rear light bub out - measured -0.02 at fuse on idle and 3,000? Same reading for real tail cluster lights.

Can't really access front sidelight bulb with probes easily.


Test 5 Current across bulb holder - High level light at idle 12.36v, but getting towards 3,000 revs fluctuated loads between 12.3 - 12.89 then fuse blew.

Rear light cluster (two bulbs) at idle 12.4 and 12.89 and the same reading at 3.000 revs.


Test 6 & 7 no tester.


8. Checked all connections as far as possible. Do you know how many wires there are behind the dash!!!!!!!! Anyway, rear high level light had a corroded terminal, but light works ok. Cleaned it anyway,


9. Checked battery earth cable, showed signs of corrosion arounf eat=rthing point, but limited viewing. Managed to undo cable and get it cleaned (shiny) and put back together. Reverted to anglo saxon phrases a few times in the process.

Didn't check voltage on earth as I have only just read that and I am also out of fuses.


Still blowing fuses only on that circuit and due to stock problems I did use 10A fuses as suggested by other people but it blows those as well!


Thanks again for all the help, hope this is of some use, or do you need fuse tester results as well?


Took a while to do the tests as it requires two people as I can't reach the accelerator whilst balancing on a dodgy step ladder holding a tester, probs and bulbs!!!! (lol)





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Hi again,


Thanks for the results above, whilst not appearing to prove any reason for the fuse blowing they do rule out a lot of things such as alternator over-voltage, etc.


I'm pretty sure now that your problem is as others are saying and that is a chafed wire which is shorting when the engine is revved. So now with the aid of an accomplice slowly rev the engine and watch for any movement around the engine (a good torch will help), movement of throttle linkages (if any), flexing of wiring harnesses, movement of hoses, exhaust sytem and hanging wires, etc, etc.

And don't forget to check for wires fouling on the accelerator pedal itself. In fact have you tried pressing the pedal with the engine off but lights on?


Finally do you get much vibration through the body at 3,000 rpm? Could a wire be vibrating and shorting? Can you disconnect the wiring to each light after the fuse or at any junction or splitter to try and narrow down the search?




PS Have you read 'KevandAli's recent thread on wiring problems with a Ducato? Link It's a rather long thread but shows the way some problems can result in the most unusual happenings.

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