You could replace the capacitor with an ignition condenser as long as the microfarad value is the same. Might have to go through the various manufacturer condenser listings in the Mercotronic manual to find one that is .15 uF value and figure out a way to mount it where the original capacitor is or you could also mount it where the contact set is as long as the lead is connected to either the black or yellow wire and the case of the condenser connected to the other wire looking at the pictures you posted. Just a suggestion if you happen to have one on hand that is 0.15 uF value. Then you could just cut one of the leads on the original condenser and bend and tape one of the cut leads and just leave the old condenser where it is for a reference of the correct value in the future.
I would suggest purchasing a condenser from a reputable electronics component supplier rather than off of ebay – just my personal preference as you do not know whether the ones on ebay are ones that a manufacturer or supplier dumped because they were out of spec or?? and as a result the quality may or may not be what you desire for use in a test tool.
Here are a couple of links to a capacitor that should work to replace the one on the Mercotronic and these are only suggestions – you may have an electronics store or supplier close to you that can also supply a similar capacitor. The other thing to keep in mind is that replacing the capacitor may not fix the problem of the low meter reading. Having said that if the capacitor is original it would be wise to replace it from an age point of view the same as if a customer had an engine the same age as your Merctoronic and still had the original condenser you would probably recommend replacing the condenser because of the age of it as good preventive maintenance.
Don’t know if your still hanging around but
I ordered this Mosuer. Seem small to me
but as I don’t know anything, I could have
ordered the wrong thing and I can only relate
to this visual. Need some guidance.
Tubs
It’s correct, the newer capacitors are much more compact in size now.