Kean Maygib sprung plunger pickups?
That round receptacle by your feet, to the right?
Yes, put them in there. Put something else on top of them, and never think of trying them again.
*Nobody* seems capable of getting them to work properly. Probably not in the last thirty years, As you’ve found, there are problems constructing them. And then, even if you’ve built and installed them, the spring pressure is either too light to work and collect current, or too strong and your locomotive has the equivalent of driving with the brakes on. They seem to work well in 7mm and larger, but for 4mm there are too many challenges.
If I ever find I have a set on my hands (usually because they have been included in an Alan Gibson kit, I usually find someone who doesn’t know better will give me a couple of quid for them via a well-known auction site.
You will find a set of coiled phosphor bronze wire pickups to be much easier and reliable to make and to use. Or try split chassis collection. I’ve moved to that recently, and certainly won’t be going back.