0 or 5k ohm Plug extenders?

[TV8]

following on from Dave COG post about lead resistance, I thought I would check my plug extenders as sometimes the car doesn't feel it is running 100%.

Sure enough, most of them were around 5k ohms which was printed on the casing but one of them appeared to be open circuit or no measurable resistance. I had some spare from the last car and looking through those, there was a slightly different part number and no 5k ohm stamp on them.

I have changed what I assume is the dodgy extender and the car is running a lot smoother but I now have seven 5k ohms and one 0 ohms extender.

It is probably worth changing all of them but why the difference and which one is correct please? My current car has Red Magnacors put on by the last owner if that makes any difference?

Thanks in advance

[TV8]

Thanks everyone. How do I tell if the plugs are resistive or not please?