Citroen DS Instrument Cluster Lighting

Recently during a night drive I discovered my Citroen DS instrument cluster lighting had failed.    In Sydney, where I live, this is a huge problem as the city is bristling with speed cameras.     So many that I could lose my entire licence in about 10 minutes driving near my house doing only 10 km/h over the speed limit.     I regularly drive at night, so I needed to find a solution.

My first assumption was the rheostat had failed.   The rheostat is the dimmer that lets the driver control the brightness of the instrument cluster lights.   Over time, these can develop dirty connections.    On the DS, the rheostat is actually not part of the cluster, but under the steering wheel.   This made it easy to test.   Once I had removed the instrument cluster I could use a multi-meter to check that I was getting 12v to the pin for instrument lighting.    I was.

Next step was to check the cluster itself.   It is simple to remove on the DS – four screws, three electrical connectors and the speedo cable.   Another four screws opens up the cluster.

At first glance, there did not appear to be anything wrong with it.   I didn’t think it would be a blown bulb because there are two of them and both were working before it failed.   In any case both bulbs looked good.

Readers who are familiar with the DS will immediately spot that my instrument cluster is not correct for a 1970 model car.     It is either a 1973 model or has been pieced together from multiple models years.    How do I know?   For 1970 and 1971 the instrument clusters had long needles for the speedometer and tachometer, and the braking distance was a ring set above the speedometer needle.    Specific to 1970 models was markings on the speedometer for the shift points.    In 1973 the clusters went to long needles and some time in 1973 the indicator lights flash together on the dash rather than separately.

When I purchased the car it had this cluster with a different MPH speedometer with a short needle.   Later, I changed the speedometer for a KM/H unit and the front cover for a nicer one.   I don’t know if the entire cluster or just the speedometer was changed in the past.   I keep an eye out for the right 1970 cluster with shift points for a DS21 but so far I have only ever seen the D Special/D Super unit.

After doing more testing I found that the cluster could light up, but it was extremely sensitive.   It would stay lit up if the cluster was dismantled and not in the dash properly, but if i bumped it or re-assembled it the lights would no longer work.

I also noticed that one of the bulb holders was cracked so I changed that one.   That change seemed to make it a bit less sensitive, but now knowing the root cause I’m not sure that was actually the case.  I would get it back in the car and it would work until pushed back into the dash properly.

At this point I was really stumped.   I got out my spare parts instrument cluster and dismantled it to see if I could spot any differences.     Perhaps there was a bad connection in the cluster somewhere?  I removed the circut board on the parts cluster which is the simplest circuit board I have ever seen.   There are almost no electrical components, just copper channels to direct power to the various bulbs.    The board is so simple I couldn’t see how a bad connection would even occur.

I went back to the good instrument cluster and removed the circuit board to compare.   This immediately showed up the problem.   There is a crack in the board!  The place it is cracked has two functions only – power and ground for the cluster lights.   The crack was not noticeable until the board was removed which was why it was so intermittent and why the cluster was not working pushed back in the dash with more pressure against it.

Now I know the problem it should be a fairly simple repair.   The board is so simple even that thick section has only two tracks.     I’m not sure if the crack has been there a while and it just got worse removing the cluster for the fan light, or if it somehow cracked during that modification.