Hi,

I have the late 1993 wiring book.
and it shows a yellow wire +12V to the Right brake light.
The yellow wire comes from Pin 11 of the Bulb out sensor.
Check that you don't have wires reversed on the right side.

It's possible that Pin 11 on the Bulb out sensor has gone open.
Easy to check and re-solder if its bad.

Find my review of the Auxito red 1157 LED brake light.
The standard 1157 draws 28 watts
The LED draws 6.8 watts. a little brighter and a lot less current to
toast the lamp socket and melt the bulb out sensor.
Dave Stevens found them cheapest at Aliexpress. (Chinese Ebay)

Use ACZP on the lamp and socket.
See here for a detailed write-up by Brickboarder Ron Qwas.

http://www.sw-em.com/anti_corrosive_paste.htm

Using ACZP can help prevent a lot of wiring problems in all old cars.
Hint: Get a bottle of Penetrox-A
I found a 8 oz bottle for about $19 at ebay

Bill