I am told that only one side lights work when reversing. Is this true?

all fuses good, and not loose.
no car told
no year told
no engine size told and that tells me what transmission is there
no country told some car in some countries have 10 engine choices
is it stick shift manual trans or automatic-trans.>>>
Lights both. not just one,
some electronics fail hot,
good ,bad, intermittent and thermally sensitive.
the 4 states, or 5 if it is vibration sensitive,
this is what I do ,as at tech fix all those bad ways doing tests.
no car told gee 100 years of cars, must I post them all>?
in the olden days for 80 years the transmissions PRNDL switch on the side of the automatic box, ,the R pin goes to both reverse lights and loves to fail or gee the connector to is lose. super simple this,.
and 1 meter test and bin
then about 2000 , year they were not happy with 1 computer(ECU)
then needed more, lots more even 10, and now car makers make more money fixing them than selling them.

so NOW they havea TCM , transmission brain and the transmission tells the TCM brain what gear you are in, then it tells the BCM body puter to turn the reverse lights on and does,. (fuse reverse not blown)
now you are and expert and no car told yet,.
history is super important to any tech for sure EVOLUTION of it.
it will only get worse,
whats next a computer in the heated seat>?
on the 2000 cars we MUST scan the PCM to see why if fuses good.
and worse, some cars mine has no fused seen, it is a regulator in the BCM that shuts down at any short.but auto resets when I cure the shorts. if the car has trailer hitch many are wired buy GOONS
with DT's
and short.
or previous rear collisions not cured fully.
no car told so text too long but now you know.

NO YEAR CAR TOLD OR COUNTRY 1997 to present, not told

is this a UK car RHD right hand drive,, drive on right side?
called also in UK Hyundai H-1 a VAN.
NO LAMP TOLD! (guess right side car and guess right side park dead not right side blinkers, correct? not told

CARS HAVE A BUNCH OF LAMPS.
THE CARS USERS GUIDE COVER THIS. GLOVE BOX, LOST?
front lamps, rear lamps
or side park lamps
reverse lamps, parks, turns, blinks, brakes or side of lamp park lamps.
sorry I cannot guess them all all 4 sides,ends are all different
or say RIGHT park lamps dead. (or 1 of 2 there) if true.

the manual is by year not told so showing it to you is impossible

The backup light switch is on the left side of the transmission. It should be hex shaped with 2 wires coming out of it.

you got a bad sycronizer in the tranny......

You are being told correctly
Something in the valve body is not installed corectly

i have a 1993 t bird auto zone is rite

On the side of your transmission will be a switch with several wires coming out of it. This is your reverse switch that turns on your reverse lights and most likely needs to be replaced

not a plug , though kinda looks like one , but a neutral safety switch at the transmission (follow the wire to side of trans case)

Yeah it's definitely the switch. Basically doesn't sense that the car's in reverse so won't turn the lights on. As far as where it's at...that I can't help you with. Volvo's tend to be a little odd...