instrument problem

24th February 2015, 18:30

I've had my car in bits for a while now and I've finally got it running again but for some reason the rev counter now doesn't work!.I've looked in my Haynes manual and checked the wiring and the earth and power seem fine,checked the continuity of the signal wire to the ECU and that's fine.also found the signal wire has 12v going through it.is this right,re 12v on signal wire?,I've removed the original ignition switch,could this affect it somehow?.thanks,hopefully someone can help,I've not much hair left!!!!

18th March 2015, 20:08

Quote:

Originally Posted by charlie2

I've had my car in bits for a while now and I've finally got it running again but for some reason the rev counter now doesn't work!.I've looked in my Haynes manual and checked the wiring and the earth and power seem fine,checked the continuity of the signal wire to the ECU and that's fine.also found the signal wire has 12v going through it.is this right,re 12v on signal wire?,I've removed the original ignition switch,could this affect it somehow?.thanks,hopefully someone can help,I've not much hair left!!!!

Hi. I'm far from being an expert here but a couple of things occur to me. I was an electronics engineer for many years and whenever I needed to study some piece of equipment I always tried to get hold of the appropriate technical handbook or data/applications sheet. Haynes manuals are good but far from exhaustive. You need a lot more info than they normally supply. But you know all this. It's a waste of time asking Citroen or the dealer who originally sold the car. A signal from the crankshaft is not likely to be generated by a permanent magnet as a coil passes by so a small current flowing in a coil will do the same job, hence the 12V appears at the ECU terminal, maybe. But unless the chassis is the earth return it needs another wire for the signal. How many wires has it got? There should be no 12 volts on any second wire as the triggering device passes the pickup coil, but this will only last for a few milliseconds, during the signal. After that both wires could have the 12 volts on. To check this out you really need an oscilloscope. Bad news I know, but there it is, for what it's worth. Like I said I'm not an expert on this rev counter. I've only given you something to hopefully spark the grey matter.