If you install an EasyCap with the old condenser still connected, the two will
be connected in parallel. If the old condenser failed totally open circuit, then
you may be OK for the time being. However, an ignition condenser rarely fails
open circuit, and you can't be sure it will stay that way. More likely, the old
condenser has gone leaky, in which case having the two in parallel will give you
the leak and too much capacitance.
We therefore recommend that the old condenser is removed or disconnected, as
described in detail in the 'condensectomy'
pages on this website.
Of course, if you're stuck at the side of the road and have an EasyCap handy, it
might be worth a try fitting it ... it only takes a couple of minutes ... and
you may strike lucky, but probably not. If you do, we would recommend performing
a condensectomy on the old condenser at the earliest opportunity.