In my memory of FIATs fitted with 'check control' features, it was the Tipo that introduced the idea of the pad wear sensor on one side only.
To be honest, it makes good sense since it cuts in half the risk of false warnings, which are common due to negligence in maintenance. Sometimes the wires simply fall off the pad, other times the wire gets trapped/cut by other bits (as mentioned by BBS) - very often it's not hooked up at all which gives no warning anyway.
The earliest systems (e.g. on the Croma/Lancia Thema) had a wire loop in the pad - two wires back to the car - thus giving a two-stage warning; stage one being when the wire earthed, stage two being when the loop was broken. Of course, if the wire was left off, the system gave a warning as well. I like this, it encourages us to get everything working properly
However the cars were soon modified with a jumper across the two-pin plug and a single wire to the pad. I suspect this was due to an exceedingly-high number of false alarms (with two wires, double the chance of breakage...) and anyway, the single wire gives a two-stage warning of sorts, since if only just worn enough, the wire contacts the disc only when braking. But it does mean that if there wire isn't hooked up properly, there won't be a warning.
I don't remember a single case where the wear indicator actually came on to indicate wear... and I do remember a case where the pads wore right down to the metal on a Thema, and of course the sensor wire wasn't connected... and being the modified system, there was no warning...
In other words, thought I've spent many happy hours making adaptor leads to connect-up pad sensor wires, I've never seen one actually work when needed
-Alex
