Electrical issue

As some of you know, I'm plane sitting for a friend. It is a 1983
172RG. Over the past couple of weeks, it seems to have picked up an
electrical issue. Occasionally, the "low voltage" light will flicker.
So far, I've seen this happen 3 times in about 5 weeks. Once, I
happened to be looking at the engine instrument panel when it happened
and both of the fuel gauges pegged to empty and then recovered during
the event. It happens so fast, if you are not looking at the panel when
it happens, you would miss it. So, I'm not sure how many times this has
happened without me knowing it.

Has anyone seen a similar problem and can point me in the right direction?

I already talked to a mechanic. His first thought was to continue
flying until the problem occurs and doesn't clear. (Basically wait
until it totally breaks.) I told him my concern about what this may be
doing to the avionics. (If the voltage is spiking low it could also be
spiking high.) After I explained this to him, he changed his tack and
said probably the first thing to do is to pull the cowling and check for
loose connectors, bad grounds, etc.

I'm just not sure how much I trust this guy.