Gents, My O2 gave up last week.... It was only 2 months old! Thats what you get when you buy cheap ones! Anyway. I can get a new Bosch 4 wire sensor very cheap! Question is.... Will it work? Engine is Digifant and has a 3 wire O2 currently.
not absolutly sure but you will have to conect the heater and sensor -ve wires togeather (or just earth the heater -ve to the body work come to think of it), then it should work. they are usually heat proof wire and are an arse to solder tho!
PM pigbladder - he got genuine ones from Ebay for cheap, will be able to give you the blokes name. But yes, the extra wire is a ground. One white wire is a switched positive for the heater, one white is a ground for the heater, grey wire is sensor ground and black wire is sensor signal.
thanks for the replies guys.... Although I found a brand new Bosch 3 wire for 30 dollars shipped I will keep an eye for a cheap 4 wire one to hook up to the air/fuel gauge.