Oh, I wasn't aware of that story.
When two batteries with opposite polarity are connected, the one with
most power will "win" with some amount. I assume that Chucks battery
was the weak one, and that some negative voltage has been applied to
the car then. The zener diode in the OVP then acts as a normal diode,
which effectively would limit the negative voltage to the computer
circuits to approxemately 0,7 volts and then blow the OVP fuse. The
fuse blew indeed and served its purpose (and maybe the diode broke
The computer (and sensors around it which are in fact supplied with
power by the computer) apparently survived, and according to Chucks
description it functioned well for some months afterwards. It is
possible that something was harmed and finally broke down after that
long period, but that would be very rare. So, I suggest to see the
problem separately from the story.
I will certainly not rule out the OVP relay as the source of the
problem. I just can't see how it would give symptoms as described (but
sometimes the explanation is first found, when the prove appears),
unless poor connections in the OVP relay (which have been seen before)
cause a drop in the voltage supplied to the computer, which could then
cause the computer to function incorrectly.
So Chuck: You can check the voltage output of the relay (pin 2...
circuit 87E), or just try to replace it.
And by the way, the "Check engine" light came on. This i driven by the
computer, so the computer must work in general.