Citroen SM wiring - Faine 453

By: Jon Faine

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citroen sm wiring 5 citroen sm wiring 5

Jon gets to grips with the monster that sent Citroen to the wall

The Citroen SM is back on the road. I have given up waiting for the Prime Minister to visit so that he could put his hands on the bonnet and heal the various woes and afflictions. And I was starting to think it would take a miracle to fix all the hydraulic leaks that bedevilled my magnificent French tourer.

The SM was a 1970s Citroen folly, a technical tour de force but a commercial tour de farce. Not often does one discrete product line send a major company broke, but the SM pretty much did that to the established and proud company founded by Andre Citroen so many years before. But when this Grand Routiere is running properly, there is something magical about it. It is no coincidence that the SM is regularly voted as one of the all-time great cars.


I was fed up with my futile amateur attempts at fixing the frequent suspension leaks and decided it was time to consult someone who actually knew what they were doing. I topped up the reservoir for the LHM, the green mineral fluid that energises the hydraulics that make the car work, and drove it slowly and carefully to a garagiste extraordinaire who had experience with these exotic hybrids of French suspension and Italian propulsion.

A few days later, I rang for a progress report. Roberto assured me that he was well into the job, but lamented in his thickly Italian accented English "Your car is a liquor factory" which sounded suitably Gallic, exciting and lucrative, offering a sideline that might offset the cost of some of the repairs. But what he meant was "a leak factory". My instructions in response were clear and unwavering – he was to keep exploring the inner bowels of the beast until every source of green puddles were found and plugged. The car was going to be returned to good working order and I was determined to get it on the road again.


This turned out to require first of all a very thorough steam clean in order to even see clearly what was happening, followed by the simple unbolting and removal of most of the front valances and covers. Thankfully the headlights did not need to come out, access was good enough without going that extra step. Then followed the dismemberment of the front brakes, suspension, hydraulic pump, clutch master cylinder, the accumulator sphere and various suspension piping unions and joints. All were given a severe talking to, along with some other maintenance issues plus making the horns and the air con work again. My delight at the result was tempered by the magnificence of his invoice, but since I had not spent a zac on the SM for many years, it was actually very reasonable. I hope Roberto does not read Unique Cars.


Back behind the wheel, and on the road again, I soon discovered a short list of annoying gremlins, things that I could attend to in my own time. First on the list was to get the radio aerial going up and down again which meant exploring the simplest explanation first – the probable failure of the switch. It is on the dashboard and is an ovoid but simple ‘centre off’affair that sits in a gang of four switches adjoining the gauges. A few screws undone and ‘bingo’ the problem is revealed. It is not electrical at all – but mechanical. The switch has dropped in its housing resulting in there not being enough space for the lateral movement to engage the contacts. The lugs that secure the switch into the holder have popped out of their housing, simple as that. A few minutes fiddling with a long slim screwdriver and they are re-housed, the switch re-installed and it all works.

Next to attend to are a few screws and cup washers missing from loose trim – tick; and then an examination of the mystery of the instrument lights no longer working. Roberto had asked his sparky to re-connect the two-tone air horns that adorn the SM, and ever since the dash lights have vanished.


Many French cars of the 70s have two tone horns – a little squeaky "beep beep here I am and I hope you will hear me" horn called ‘town’ and a magnificent terrifying "get out of my way you insignificant little 2CV travelling at 70k on the autoroute" type ‘country’ horn. The SM powers them with a small compressor tucked in under the front passenger’s side headlight assembly and the wiring on mine had been disconnected, even though the unit worked. It simply needed a new relay, a feed of oil, some new cables to be connected to the loom and now I can cruise the highway and blast away and terrify 2CVs in two tones to my hearts content. Sacre bleu.


From Unique Cars #453, May 2021

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