Right, going through the pre-MOT checks for the beast (Mk1) and the rear fogs aren't working. No light on dash, neither fog illuminates. The front LH dip beam is ok so fuse should be ok (shared). My guess is the switch is at fault since both are not working. Haven't had a chance to check much yet as it was dark.

What things should I check - will obviously check bulbs first.

If there was one thing that has me stumped it electrics. Sure that they are pretty basic, just need to get my head around how it/they work!

work back from the bulb.
so check bulb
then check power to the bulb holder
if no power check the connections are clean
you can then check continuity from the fuse to the bulb socket etc

hade a mare once with a mk3 cav that burnt the rear fog wiring out inside the loom

thepottleflump said:

Right, going through the pre-MOT checks for the beast (Mk1) and the rear fogs aren't working. No light on dash, neither fog illuminates. The front LH dip beam is ok so fuse should be ok (shared). My guess is the switch is at fault since both are not working. Haven't had a chance to check much yet as it was dark.

What things should I check - will obviously check bulbs first.

If there was one thing that has me stumped it electrics. Sure that they are pretty basic, just need to get my head around how it/they work!

Click to expand...

I'm no expert either, but if both rear fogs aren't working, together with switch not illuminating, I would be looking at the switch/connections to switch. As you say, quick check of both bulbs and fuse are in order first, but to me, switch could be main suspect!

my fogs, brakes, reverse and indicators all had loose bulb holders, all needed to be bent in slightly, and the bottom contact bent up to get a decent connection

Also check the obvious, like make sure the switch itself is actually working. Do the fogs have a relay? That would be worth checking as well if it does (I can't remember, but I know the front fogs when fitted have a seperate relay).

Other than that, go through the obvious. Make sure the bulbs aren't burnt out, and as Turboned says check the connections. The rear lights on Unos are notorious for their connections working loose.

Check that the connecting block going into the back of the light is clean and fitted correctly. Would be a good excuse to give the connectors a clean and smear some silicone grease into them to prevent future corrosion.

Good luck with the MOT!

You're right about the electrics being 'basic'. There's no CAN-bus in the Uno, so it is literally just the switch, the wires, and the bulb-holder to worry about.

Looking in the Uno handbook (an excellent publication compared with that for the Stilo) there isn't a mention of the relays after all but on my Uno Turbo at least, there is no relay (I just checked and there isn't a 'click' even though the rear fog lights do come on).

custard boy is right, the most logical way is to start at the bulb holder and work backwards.

My contribution would be: don't assume that there isn't more than one fault, i.e. it is perfectly possible that your warning light is loose/blown AND both your tail light cluster connections are dodgy

Also, when testing a switch with a multimeter, remember that the multimeter presents a tiny current loading compared with the 2x 21W bulbs, so a switch that tests fine with a multimeter may still not allow the full current to pass (this particularly applies to electric window switches!)

-Alex

almost forgot, while you're in there, bit of tin foil, works well for a little more reflection of light out of the lens

Cheers guys, good idea on the foil, will get out there and try and fix this!

alexGS said:

You're right about the electrics being 'basic'.

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prehistoric......

Right problem sorted. I feel I got lucky. Took the switch panel out and found a wire hanging loose, pluged in a voila, all working now.

While trying to test for voltage at the light cluster I worked out I haven't got a clue how to really use my multimeter, only used it once before. I'm presuming that to measure voltage the car runs on DC. I've got a digital multimeter which I believe I need to set for measuring upto 20v DC. I'd then place the red postive lead on the springy bit in the bulb holder which presses against the base of the bulb and the black negative lead against the body of the bulb holder which hooks into the bulb surround. Sorry for the description, does that sound right? Anyone got any tips on this sort of thing!

Yep, that's the way... it doesn't even matter if you get things the wrong way around, since the multimeter will simply read a negative voltage!

Most of the time you will use either voltage measurement (as you describe) or continuity measurement. For the latter, you select the lowest ohms (rhymes with 'roams', not with 'bombs' ) range, which often has a 'sound waves' icon to indicate that the multimeter will beep. Touch the probes together to test. Then apply to the item, your two switch terminals for instance, and operate the switch. The multimeter will display a low number, being the number of ohms resistance in the switch. Typically anything over 1 ohm is cause for concern!

Multimeters can also measure current (the 'volume' of electrons flowing, voltage is like the 'pressure').

To measure current, you usually connect the red lead to a different terminal on the multimeter (marked 10A) and then the leads go in SERIES with the circuit. For example, if measuring the current draw from the battery (with the engine switched off), you would disconnect one battery terminal and place one multimeter lead on the terminal, the other on the battery itself. The multimeter then becomes part of the circuit and on the DC A range, it will show you how much current is flowing (should be almost nothing in the engine-off case). If you open a door etc. you would see the current draw. This technique is occasionally useful for discovering the source of repeated flat batteries, if you remove fuses one by one until the current draw disappears, you find the faulty circuit.

One more novel way to measure voltage drop, e.g. at the headlights. With the multimeter set up to measure voltage, put one lead on the battery positive terminal, and the other lead on the headlight bulb pin (grey or green wire). Because neither lead is grounded, the multimeter reads the voltage difference between the two points. This should be as little as possible, but frequently in the case of the Uno you lose up to two volts through the headlight switch and wiring, which may convince you of the merit of fitting relays to the headlights That two volts diminishes the light output by a frightening 30%. See http://www.madelectrical.com/electricaltech/brighter-headlights.shtml for a quick summary.

-Alex

I wish the fix for my rear fog lights not working was as easy as a wire off.

The dash fog light warning light does work on mine but nothing is happening at the rear. My bulbs are fine, checked and they work. But to complicate matters it happens my mulitmeter has just decided it won't work now, and my test light is 600 kms away! Dip lights work and all fuses are fine. I have been studying the wiring diagram with the help of a magnifying glass!! and it looks simple enough. I wonder what it can be? any other suggestions other than what is above.

Bloody hell this thread brings back memories, forgot about this one, check the earths for the light clusters maybe.

Memories - Memories ah well, a well there you go. Funny thing all the other lights are perfect, so would the earth still be the problem. Get my new multi meter this afternoon and have another look at the out wires from the fuse block.

thepottleflump said:

Bloody hell this thread brings back memories, forgot about this one, check the earths for the light clusters maybe.

Click to expand...

...brings back memories for me, too!
I wonder if you've used your multimeter much since, thepottleflump?

Most of the time, Uno light faults seem to be rear clusters (bulb holders), and the connection to rear clusters (poor earthing as said). Or, wires could be loose on the back of the fusebox.

I usually start with a wiggle of the bulbs and end up by repainting the black plastic in silver, soldering all bulb holders to the baseboard (use Duzall flux), and adding an earth wire.

-Alex

I've done the wiggle thing, pulled the connector from the fuse block, sprayed contact spray around, still no joy yet. But without a multimeter to check where the voltage end it is a bit of guess so I will save my frustrations till I get the mmeter. If all else fails there is always new wiring! And I am going to do the relay thing on the headlights as well especially high beam.

And it is 6 months till the next wof, he let me through this time.

Aha, rear fogs working again! You guys were right, my wiggle test was not good enough. Multimeter said there was voltage there, tabs needed tightened, 1 bulb thrown out, ok sometimes - sometimes not, then bulb turned in the base. Just goes to show, simple stuff first AGAIN. Thanks.

rawill said:

Aha, rear fogs working again! You guys were right, my wiggle test was not good enough. Multimeter said there was voltage there, tabs needed tightened, 1 bulb thrown out, ok sometimes - sometimes not, then bulb turned in the base. Just goes to show, simple stuff first AGAIN. Thanks.

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Good stuff. Don'tcha hate it when the glass bit turns in the metal cap - the bulb's usually history after that. I've had that happen so many times!

The good thing is that there's only two types of bulb in the Uno rear light - 21W and the small 5W sidelights, so it's worth having some spares on hand just for times like this. As you know, but just for the benefit of anyone else

I know what you were thinking before though; it's always suspicious when both lights stop working, yet it can happen when one bulb is faulty and the other is loose - concurrent faults happen quite often on 25-year-old cars

Reminds me of the non-working reverse lights on a FIAT Croma. One bulb was missing and the other one blown. I put in two new bulbs, but no joy. Checked the fuse - blown. Replaced the fuse - still no light. It turned out the reverse light wires had been connected to the automatic transmission temperature switch, not to the reverse light switch. You just have to persevere in jobs like that. I think someone must have 'borrowed' the bulbs after the connection mistake was made...

-Alex