Jim,
with the key on check that there is voltage on one of the two wires
going to the back up light switch.
it's located on the left side of the trans on manual trans vanagons.
Switch with 2 wires on it.

one of them should be getting power from the dash/fuse box area when the
key is on.
If there's power on one wire,
put it in reverse,
power should come out of the other side of the swtich, on its way to the
back up light bulbs.

they do fail , though very rare.
Another possibility ...usually only when installing a switch or trans
newly ..
Depending on the thickness of the sealing washer ..
the switch can be in too far and BU lights are always on,
or not far enough and they never come on.

the tail light housings and all exterior lights..
poor contact, corrosion and water are easily as common as burnt out bulbs.
( the front turn signalhousings need to be removed every year or so for
vanagons that live where it rains ..
those can fill right up with water - have seen it a hundred times.
Tail light housings seldom do ..
but those circuit boards need to come out of there once in a while
....get checked for rust and corrosion ..
treated with something etc.

be sure to check fuses too..though if one side is working, you know the
fuse for that circuit is ok and making contact,re BU lights.
I believe both BU bulbs are on one fuse..
though things like tail lights and head lights have a fuse for each
side, for safety reasons. You can't loose both tail lights due to a fuse
problem that way, forexample.

got a 12 volt test light ?
that can be used to look for both power and ground ?

On 9/27/2013 8:01 AM, Jim Felder wrote:
> Neither of the backup lights on my 83 five-speed 2wd is working. I had a
> chance to pull the bulb out of the drivers side tail light and it tested
> good.
>
> Do these switches ever fail? I will get a chance sunday to check out the
> wiring, but worrying in advance about a thing I have never even thought
> about before, which is how the backup light switch works.
>
> Jim
>