What happens if you try to jumpstart a battery and incorrectly attach
the positive terminal to the negative, instead of positive-to-positive
and negative-to-negative? (Specifically, jumpstarting a midsized
motorcycle with a Camry)

Dear tobym-ga,

According to these sites, it can cause damage to the alternator and
other parts of the electrics, and possibly cause the battery to
explode.

This site is on Batteries and BMW Bikes.
?Never, never, NEVER, connect a battery the wrong way round.
Connecting a battery the wrong way round will not only short (and
perhaps destroy) the battery, but is likely to instantaneously destroy
every electronic component on the bike including the alternator, ABS,
fuel injection, clock, instrumentation, diagnostic components, radio
tape, CD, and indicators.?
http://www.bmwmotorrad.co.za/bikes/workshop/tech/articles/batteries.html

This discussion on this BMW motorcycle forum indicates that the same
thing happened to some of the contributors.
http://www.motobins.com/yabbse/index.php?board=2;action=display;threadid=491

These refer to car batteries, but I?m sure they apply equally to motorcycles.

Bottom of the page.
?Great care must be taken when connecting the donor battery, if it is
connected incorrectly explosions can occur at worst or electronic
components like the alternator destroyed. ?
http://www.mgb-stuff.org.uk/electricstext1.htm

?A fully charged battery, if shorted through jump leads, can discharge
at a rate well above 1000 amps causing violent arcing and very rapid
heating of the jump leads and terminals, and can even cause the
battery to explode.?
http://www.fordscorpio.co.uk/manual/h&s/SafeWorkshop.pdf


I hope this answers your question. If it does not, or the answer is
unclear, then please ask for clarification of this research before
rating the answer. I shall respond to the clarification request as
soon as I receive it.
Thank you
answerfinder


Search strategy
"jump leads" "wrong way round"
://www.google.co.uk/search?q=%22jump+leads%22+%22wrong+way+round%22&btnG=Search&hl=en

Prompt answer included several sources of reference.