On Jun 11, 7:59*pm, JeffM wrote:
Cleo Frank wrote:
[...]bought [a] battery[...] *I did accidentally install it backwards

As has been said: high probability electronic items are smoked.

[...]the battery is now securely connected.
[...]no power whatever, clock dead, nothing.

I start with the lights, then try lights+horn.

A voltmeter is a pretty lousy tool for troubleshooting this
(well, after an initial check of the battery).
The light-bulb probes they sell in auto parts departments
are better for this--or you can make your own with any auto bulb.

Unlike a voltmeter, because these PULL SOME CURRENT,
they are really good at sorting out a YES from a NO from a MAYBE.
You can also tell Pass/Fail out of the corner of your eye.

Clip the lead hanging out the end to a part of the body
and start probing with the point.
When you stop seeing it light up, back up.
If you can't get anything from the body to the + post of the battery,
the ground connection from the battery is open.

Start out by seeing if the headlights light, that will tell you if
there is at least some connection between the battery and the rest of
the system