Noody Posted November 14, 2016 Share Posted November 14, 2016 My fog lights stopped working and I'm fairly certain as a result of corrosion at junction points. One was working but clearly struggling for volts and current. I started by undoing every cable connector I could find because I knew they would all display corrosion that needed dealing with, the problem I have is I'm working without a diagram and even though I have the Fiat book somewhere I can't find it. Not yet. I took the covers off the fuse stations but they were little use other than I systematically go through the fuses, the reason I think it may be a fuse or rely is one of the H3 halogen bulbs had gone so maybe it took a fuse with it. The rear fog switch seems to operate a relay that sounds as if its built into the switch, the front fog switch doesn't make the sound of a relay but the indicator lights comes on. I don't know what else to tell you but in the hope someone has dealt with this on 2004 2.8jtd. Link to comment Share on other sites More sharing options...
euroserv Posted November 14, 2016 Share Posted November 14, 2016 The fog light fuse is in the engine compartment fuse box. I have not got one here to look at right now but if you consider the bank of maxi fuses to be at the top, there are two rows of mini fuses, one down each side. The last but one on the right is fuse 9 and should be 15A. This is the one and only fuse for the front fog lamps. It is not uncommon to find corrosion on the terminals that attach to the bulb. Link to comment Share on other sites More sharing options...
Noody Posted November 15, 2016 Author Share Posted November 15, 2016 Thanks for that and I'm still looking for my Fiat user manual that has this information. I wonder, do you know where the relay is for the fog lamps and do the parking lights have left and right fuses because my drivers side parking light circuit is also down. Regarding corrosion, no corrosion at the parking light bulbs and fittings but all the plug-socket joining devices so far show corrosion. There had been a little corrosion on the H3 bulb plate, I live on coast so we have a salty amosphere. That H3 fitting and bulb plate looked like an aluminium alloy. Once again I really appreciate your help. I have done some online research for fog light problems but all the entries are about retro-fitting and the problems of finding fuses and a relay. One entry that coincides with yours that have yet to check because of and late darkness is engine bay fuse FO9 15 amps and relay T 17. Another entry says T17 is washers. When I get all this fixed I'm looking for LED bulbs for the fogs. Mending and fixing on a 12 years old van are like I imagine painting the Forth Bridge. Always something needs doing to keep the vehicle nice. I love this motorhome. Link to comment Share on other sites More sharing options...
euroserv Posted November 15, 2016 Share Posted November 15, 2016 The inside of the fuse box cover has a key for which relay does what. The side lights are on separate fuses for right and left. They are F12 and F13 located in the fuse box on the right hand side of the dashboard. The unit where the hazard light switch is located is also a can-bus 'node' where all lighting functions are controlled. If you have more than one lighting fault; it is often due to a failure with this node. The complete assembly with whatever option switches are installed has to be replaced (not that often though) and it has to be the same part number as the original. IE. If yours does not have a switch for heated rear windows, you can't use one that has. Because yours does have front fog lamps, this will make it a little more difficult to find a second hand one. Link to comment Share on other sites More sharing options...
Noody Posted November 15, 2016 Author Share Posted November 15, 2016 Thank you, and once again very helpful. I have moved forward slightly, one of the parking light circuits has a short-circuit on the basis of the f13 fuse had blown. Are these 5 amp fuses up to the supply of current for all those marker lights connected to the circuit ? It's over 20'watts each side. I'm working on it and will report any progress. A clue is that I have been working on the van and I had a new Stainless Steel exhaust fitted. Maybe one of us buggered something. I'm checking my work right now by slowly isolating sections. Link to comment Share on other sites More sharing options...
Brian Kirby Posted November 15, 2016 Share Posted November 15, 2016 Noody - 2016-11-15 4:04 PM.................... Are these 5 amp fuses up to the supply of current for all those marker lights connected to the circuit ? It's over 20'watts each side..................... Volts x Amps = Watts, so a 5 amp fuse @ 12V should be good for 60W. Don't be confused about fuse ratings. The fuse is there to protect the wiring from overheating under excess load, not to protect the actual load. Fuses are invariably rated below the actual load on the circuit, because the wiring must be suitable for whatever load is likely to be connected. If the load were more or less equal to the wiring capacity, the wiring would run hot, so the fuse will be rated lower to provide an added safety factor by ensuring it fails before the wiring heats significantly. Link to comment Share on other sites More sharing options...
Noody Posted November 16, 2016 Author Share Posted November 16, 2016 Thanks Brian, I was scratching my head to remember how to work out it the load suited the fuse. The fog lights being a problem I'm assuming is a red-herring, the cause is a fault in the parking light circuit and I may be responsible for that fault. So far I checked two out of three possible places I may have damaged the wires, they were fine. Third place is where I had to drill holes alongside lighting wires, I was aware and very careful so will be surprised if I caused the fault but it's all I have to go on at the moment. The lighting is down on the left side, it was the left side I've been working on. Far to much of coincidence. Presumably the fog light relay needs power from the lighting circuit to switch the relay ? Link to comment Share on other sites More sharing options...
colin Posted November 16, 2016 Share Posted November 16, 2016 Brian Kirby - 2016-11-15 5:01 PM Don't be confused about fuse ratings. The fuse is there to protect the wiring from overheating under excess load, not to protect the actual load. Fuses are invariably rated below the actual load on the circuit, because the wiring must be suitable for whatever load is likely to be connected. If the load were more or less equal to the wiring capacity, the wiring would run hot, so the fuse will be rated lower to provide an added safety factor by ensuring it fails before the wiring heats significantly. I've read this several times and either i'm having a bad morning or you where on the sherry early yesterday. The fuse will be rated below the capacity of the circuit wiring, if it where rated below the actual load it will blow every time. Link to comment Share on other sites More sharing options...
Noody Posted November 17, 2016 Author Share Posted November 17, 2016 (smile) Ok-ok, a fuse is there to protect the wiring from melting in the case of an overload. What Brian is pointing out is that fuse ratings are to deal with the expected load. Each and every conductor size will have a safe working load, the fuse rating will be somewhere between that and the expected load though I think if you do the maths you'll find as in the case of my lighting circuit the added marker lights were accounted for when Fiat did the fuse ratings. One thing that worries me is that if the fuse is very small and the circuits have enough corrosion, that corrosion will represent a short circuit. Particularly at 12 volts. Link to comment Share on other sites More sharing options...
Noody Posted November 17, 2016 Author Share Posted November 17, 2016 Further to my previous post, the comment about high-resistance emulating a short circuit if that resistance is high enough. I'm now wondering if this has been the case with my fault. Here is what's happened, I disconnected the left hand marker light circuit and proved it ok, but, at one point at spade connections the conductors were heavily oxidized within the spade connectors. With that circuit disabled I plugged the fuse back in and everything is working yet that marker light circuit doesn't show any resistance using an ordinary digital multimeter. Any thoughts ? Link to comment Share on other sites More sharing options...
Alanb Posted November 17, 2016 Share Posted November 17, 2016 Hi Richard, I refer to your latest post on this subject. You state that a high resistance could become a short circuit if it was high enough. I am sorry but you seem to have got this the wrong way round. A short circuit is a very low resistance. You also query the you cannot measure any resistance when testing your marker lights circuit. Do not worry this is to be expected. A 20W bulb operating at 12V would be expected to show a resistance of about 7.2 Ohms. Resistance is roughly proportional to absolute temperature, and ambient temperatue will be about 300K (273K = 0Centigrade). The operating temperature of the tungsten filament will be in the region of 5000K. This means that the cold resistance of the bulb(s), will be about 1/16 of the operating resistance. Divide 7.2 by 16, and you get 0.45 Ohms. Not much too measure! Alan Link to comment Share on other sites More sharing options...
Noody Posted November 17, 2016 Author Share Posted November 17, 2016 Err ???? Its been a long time, my electronics are amateur radio from 40 years ago and maybe its my vocabulary rather than understanding. Ill let you correct me. Two parallel conductors not connected (open circuit) will produce a 0 resistance reading, if you short those two conductors you get a short circuit which amounts to a 0 resistance as you say , if you place a bulb of (Say 5watts) across those conductors you will see a resistance of around 3 ohms (Its what I'm seeing, sometimes over 4 ohms) depending on any connection resistance. If you take the bulb away its an open circuit, if you place a conductor across those parallel conductors you get a short circuit ? Where am i going wrong ? And I do appreciate the help. Link to comment Share on other sites More sharing options...
Mick Bajcar Posted November 17, 2016 Share Posted November 17, 2016 Noody Your terminology is wrong. In your example, two parallel wires unconnected will show an (almost) infinite resistance, not a zero resistance. A bulb connected will show a few ohms Mick Bajcar Link to comment Share on other sites More sharing options...
Noody Posted November 17, 2016 Author Share Posted November 17, 2016 Back to school eh Mike, thanks. How do I describe what I read on a meter when you short those parallel conductors ? Link to comment Share on other sites More sharing options...
Mick Bajcar Posted November 17, 2016 Share Posted November 17, 2016 Noody That will be a very low resistance. How low will depend on the thickness of the cable and its length. but pretty close to zero I would imagine on a digital meter. Do your issues make it a motor ohm ? Perhaps even an ohm from ohm :-D Mick Bajcar Link to comment Share on other sites More sharing options...
George Collings Posted November 17, 2016 Share Posted November 17, 2016 Poor earthing is a the root of many an automotive electrical problem. Suggest you establish a good earth point and run a duplicate earth lead from the bulb holder to it. Ideally if this improves or cures the problem find the corrosion in the earthing but sometimes its expedient to just run jury rigged permanently Link to comment Share on other sites More sharing options...
Noody Posted November 17, 2016 Author Share Posted November 17, 2016 (Smile) Thanks Mike, I'm sure I understand though conveying my thoughts can be a problem. George. Right now the problem has disappeared after isolating and testing sections that showed no fault other than corrosion and oxidized conductors though I figure as you suggest that this is to do with not only corrosion at connectors but mostly earthing and installing multiple earth points rather than relying on whatever has been provided could be a solution? First I suppose I need to find out how far above the battery negative various circuits are so I made a long lead though I'm not entirely sure if all negative paths are direct or switched. At the moment everything is good and I do appreciate all the comments. Link to comment Share on other sites More sharing options...
Noody Posted November 27, 2016 Author Share Posted November 27, 2016 Time has come for me to share results, and what an endless session of one problem after another. Whilst I'm sorting the electrics my key got stuck in the lock barrel. I'll make that another thread. Yes fuses were blown but you have to find a culprit, this time it isn't Fiat I'm bitching about but Burstner and maybe Hymer group. The Hella fog lamps have a plastic rear end that melted from the heat produced by the halogen bulbs. That is why the fuse blew though I still don't understand why the parking light circuit fuse came out in sympathy. I'm not replacing those fog lights and although fitting LED bulbs will solve the heat problem those Hella lamps are £50 each and quite frankly they are a piece-of-poo. So I'm repairing them. It took six hours to get three corroded screws out so I could remove the light body. I thought you would like to know. Link to comment Share on other sites More sharing options...
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