911 Porsche World - - Practical Porsche -

Take a good, hard look at the largest of the half-dozen pic­tures be­low. It shows, fairly ob­vi­ously, just a small sec­tion of a ve­hi­cle wiring loom, the sev­eral twisted pairs of wires that I hope you can see fur­ther in­di­cat­ing that it is from a mod­ern car with a so­phis­ti­cated CANBUS-BASED elec­tri­cal sys­tem. Look more closely still and you will spot, I hope, that a num­ber of the con­ven­tional ca­bles have on them the short lengths of sub­se­quently fit­ted heat- shrink tub­ing that usu­ally sug­gest, well, who knows what hor­rors be­neath.

Let me now tell you that this morass of plas­tic and in some places ex­posed and elec­tri­cally live cop­per wire is the group of ca­bles pass­ing from the cabin into the front com­part­ment of a late-model 911, and thus – you would rea­son­ably sup­pose – fairly sig­nif­i­cant to the safe and re­li­able op­er­a­tion of the car’s many sys­tems. (Yes, I know this col­umn has had a bit of an elec­tri­cal theme this month, but I trust you will agree that it has been both in­for­ma­tive and use­ful.)

And not just any late-model 911. In fact, it’s none other than a 2014 991 Turbo, even on a bad day still worth per­haps £100,000. It had been brought to Sid Ma­lik’s Porsche-torque work­shop in Uxbridge, Middlesex, with the PSM warn­ing light on, and it hadn’t taken Sid long to find out why. At least two of the wires – to the PSM’S nearby ac­cel­er­a­tion sen­sor – had been trans­posed, de­spite their clear colour-cod­ing, and once that fun­da­men­tal er­ror had been put right the warn­ing light went out.

Even so, it took Sid many more hours of painstak­ing work gen­tly to sep­a­rate and minutely ex­am­ine the per­haps 100 or more ca­bles for any other dam­age, mak­ing good any sus­pect con­nec­tions in­side the heat-shrink tub­ing, and most cer­tainly re­pair­ing the ca­ble whose in­ner strands had ef­fec­tively been blow­ing around in the breeze. Pre­cisely why some­one had been in there be­fore him, cre­at­ing such may­hem, es­pe­cially in a car of this huge per­for­mance and sub­stan­tial value, re­mains un­clear, but ei­ther way the fi­nal bill – for two days’ work, some of which in­volved Sid lay­ing on his back in the driver’s footwell, try­ing to see what was go­ing on deep in­side the fas­cia – was surely the bar­gain of the year.

991 Turbo ar­rived at Porsche-torque with its PSM ac­cel­er­a­tion sen­sor show­ing con­ti­nu­ity is­sues, so Sid Ma­lik started fol­low­ing the ca­bles back into the car’s main loom. It was soon all too ob­vi­ous that some­one had been in­side that be­fore, where it passes from the cor­ner of the front com­part­ment back down into the cabin. Peel­ing away the clearly dam­aged outer sheath­ing re­vealed this frankly hor­ri­fy­ing sight (top) and, teas­ing the in­di­vid­ual ca­bles apart, that many had been cut and then re­con­nected. At least the joints had been sol­dered (al­though that method can gen­er­ate a high re­sis­tance that might cause prob­lems in fu­ture) and cov­ered in heat-shrink tub­ing, but in at least one area there were ex­posed live ca­ble strands. The orig­i­nal PSM prob­lem was traced to two wires be­ing trans­posed, de­spite their clear colour-cod­ing (solid green, and green with a blue trace). Ide­ally the re­pair would re­quire a new grom­met, too (above, far right), but since that would it­self have to be cut in or­der to pass it round the mass of ca­bles Sid prag­mat­i­cally re­tained the orig­i­nal, mak­ing sure that it was pushed cor­rectly into po­si­tion, and thus seal­ing cor­rectly. Dis­as­ter averted. But it was a close call

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