Citroen XM Forum

Hi guys,

I thought I would post this before I dig deeper myself, but when my indicator/hazard lights are on, there are small power dips whenever the indicator lights are on, causing the taillights as well as the interior lighting to fluctuate in brightness. On the taillights this is an MOT failure, so I'm looking to fix it.

I first suspected the grounds on the taillights themselves, but as the interior lights display the same problem I don't think this could be the issue.

Does anyone know what the most likely culprits here could be? I heard that sometimes the grounds in the engine bay corrode and that this could be the issue.

Thanks!

EDIT: Citroen XM Y4 break btw

All Xm do have some voltage drop through the wiring, but if it's particularly noticeable through the whole car it could be a battery clamp/lead, or Gnd issue.
The crimp on lead battery clamps do suffer corrosion at the cable crimp. Replace them with clamp on ones.
It may also be worth checking the battery to fuse-box feeds.

You really need to load test the wiring, whilst monitoring battery voltage. to be sure.
Have you metered the battery voltage when the engine is running? It may be low, which will cause more current to be drawn.

The rear lamps wiring is a bit messy, passing through three connectors down the length of the car and the Gnd going in the reverse direction all the way to under the steering column, though as your issue is over the complete car, it's not a rear lights issue, as such.

I too can see voltage drop when load is applied, such as pressing the brakes, though I haven't noticed the indicators/hazards showing the effect.

The MOT tester is only interested in interference between lamp units, normally caused by the tail lamp Gnds being poor. They will allow for some voltage drop causing slight dimming: as long as no lamp causes another to partially illuminate, or dim severely, they should be satisfied.
Do the lamps stay properly illuminated when all are switched on?

One doesn't normally see this effect now as most cars have LED lamps, so much lower current consumption. Multiplex wiring also helps as a few thicker cables carry the high current round the car and signal wires not only being very low current, but irrelevant to the actual lamp power.