I have a 1992 civic hatch manual tranny. The reverse lights weren't working so I replaced the reverse light switch but after replacing the switch the reverse lights were staying on all the time not just when backing up.

Why after replacing the reverse light switch are my reverse lights staying on in reverse, drive and park?

Despite this I must continue my day and as I am driving to work, I suddenly cannot downshift from 5th gear. I can shift perfectly through all other gears up and down but once in 5th it sticks and takes some time and persuasion to come out.
I took the new reverse light switch off and put my old one back on and now it shifts perfectly through all the gears again. Why?

Why was 5th gear sticking with the new switch in and not when I put the old one back on?

 

Who'd you get the switch from? I'd take it back and ask for the right one.

 

got the switch new from autozone. so you think it just wasn't the right one for my car?
do you know how I can figure out which one is the right one for my car since they don't seem to know?

 

take the original one with you to compare the length that goes down into the trans.

And yes, I've had many problems with AZ parts,(and other places too, but them most of all) you just have to double check them.

 

I have read in the past where wiring near the hatch area grounds and lights stay on..

Might want to search for that as well before buying switches all over town.

 

It does sound like a grounding issue.
If worst comes to the worst, you could always run a cable through the body paneling and into the light cluster at the back (I think the feed goes to the right hand cluster then is daisy chained from that).

The reverse light on my partner's civic wouldn't work at all, which turned out to be a problem in the loom.

The downshift sounds like the synchromesh is having issues.
Can you shift down from 5th if you double declutch?