I had to lie down after I read it. And yes, I read it. And it was mildly fascinating.
A big thanks to all the technical guys here who understand this stuff, and through no fault of their own, help us laymen to understand what the parts in our Volvos do.
Recently my fuel pump relay went bad. The first instinct was to jam a piece of thin cardboard between the poles on the point of the coil to keep it closed. This is essentially the same as putting a jumper.
After replacing the capacitors 100µF, 22µF I plugged it back in the car. To my surprise it kept cutting the coil off and on erratically.
So I took it back to the lab and started to decode the function of the PCB to figure out what exactly this little bugger does, and is it really necessary.
MVS Moderator Ozark Lee:
It also cuts off the fuel pump if the engine dies which is a desirable trait after you run into a tree and break a fuel line.