my 300d turbo diesel 84 has vac leak i have narrowed it down to a yellow plastic pipe with a blue line its at the firewall it rnters the cabin its way up near steering column anybody know where it goes im pretty sure it does not go to doors engine wont shut down because of leak im tired of pulling panels and not finding it id appreciate any help

This lovely schematic says it could be your reservoir:

https://www.google.com/search?q=w123+vacuum+schematic&rlz=1C1CHBF_enUS863US863&sxsrf=ALeKk00_q-nPfQzl_JBrOSwJyevGezFg_Q:1595987818704&tbm=isch&source=iu&ictx=1&fir=_STLt5cwJziHmM%252CKjFrDJrsK4jxWM%252C_&vet=1&usg=AI4_-kSw8fU-R4MaZa5TF0VknUOVu25ztg&sa=X&ved=2ahUKEwiVtP_3rfHqAhURVK0KHW-5BkMQ9QEwAHoECA0QIA&biw=1536&bih=722&dpr=2.5#imgrc=c3bWoi4ue2LxmM

Try plugging your door locking system completely and isolating it to see if it's the cause.

thank you for your help with vac leak you were right it was at reservoir where the plastic pipe enters res. i was taking cardboard to recycle and piece must have pushed pipe that caused leak next time i will start at res.and work forward thank again for your help