multiple light failure warnings but rear connectors OK

Apologies for what appears to be a common question but I too am getting the multiple bulb failures warnings and I have checked the rear lamp connections and all are good, clean, no sign of burning etc. I checked all the bulbs and seatings too and all look as new.

Any ideas on how to fix this then? Do we know if the overloading of the wiring on the rear clusters that is mentioned as the cause for this applies to other bulbs/connectors as well?

Or any way of (temporarily) disabling the fault warning system? I know this is a sillyish thing to do but I am going on a long journey and will be driven insane by the constant warning beeps! The fuse diagram in the manual bears no resemblance to the under bonnet fuse box but it does mention a fuse for "warning".If I can find this and pull it will I disable the warning system (or do you think it refers to the hazard warning lights?

Any ideas appreciated!

Hi reg

I don't think there is a separate fuse for the warning system or a way to disable.

My suggestion would be to establish whether your problem is the lights or the monitoring system. Only then can you look at a solution.

With there been more than one light causing an error message I would look at things which are common to the rear lights, the obvious one being the earth/chassis wire. If you can't find the rear earth point, an easy way to check is to measure the voltage from the earthed end of the bulb to a good earth point on the bodywork, eg a metal fixing or bracket. With the bulb on you should get virtually zero volts.

Not quite as scientific but do the bulbs which are supposed to be faulty look OK, are they as bright as they should be?

If you have a meter that measures current, measure the current in one of the light circuits. To do this, the meter needs to be in series with the circuit, connectors are usually a good place to break into a circuit. You can calculate a rough value for expected current using the formula I=P/V where P is Power (the wattage of the bulb eg 5W for a sidelight, 21W for brake lamp), V is voltage (nominally 12 volts, although check this is the case, if it is too low it might be a cause of your problem) and I is the current which you will be measuring.

As an example, for a 5W bulb:- I=5/12 = approx 400mA.

Bulb failure circuits work by measuring the current, if its too low they will show a warning.

If the bulbs are working correctly then the next place to look is the circuit which does the monitoring.

One final thought, do you have LED bulbs? These can upset bulb failure monitor circuits.

Thanks for the comprehensive advice - much appreciated.

The thing that puzzles me is that the alleged failures are all over the car - indicators, reversing lamps, brake lights, fog lamps, side lights. So not just the rear light clusters.

Normal bulbs, not LED.

I will have a look to see if they are as bright as expected, and dig out the multimeter and do some testing. It looks like I need to be testing many of the lighting connectors/bulbs, and the ones at the front are a pig to get at (I have big fingers!).

My money is on a systems fault rather than the lighting bulbs circuits so I wouldn't go too far testing circuits. If you can establish that a couple of circuits are working as they should then it's all pointing to the monitoring system. Do check the battery voltage though, cars with computers can do all sorts of strange things if they don't have a good supply. Also have a look at the battery terminals and the battery earth strap. Any poor or corroded connections can cause problems.

Thanks. It does sound like a module or power issue, that makes more sense.

If I disconnect the battery and clean up the poles I assume that I will need radio code (not sure if I have that). are there any other pitfalls associated with disconnecting the battery? (My last two cars (Merc and Jag) were a nightmare if you lost battery power).

reg091 wrote:f I disconnect the battery and clean up the poles I assume that I will need radio code (not sure if I have that). are there any other pitfalls associated with disconnecting the battery? (My last two cars (Merc and Jag) were a nightmare if you lost battery power).

You won't need a radio code if its the factory fitted stereo system, some battery removal/disconnecting tips are Here.