first check your bulbs to see if they are loose or you might have some rust and its not getting agood connection,and check your fusible link,its tied into your positive battery cable.
check out ebay.
no 84 and 85 swap out.
where is dash light and tail light relay on 1984 nissan pickup truck
85 and some 86
185R14
no 84 and 85 change out.
85 720
It is located on the right side below the gas cap.
Get your alternator tested at autozone,its free,and check your battery too.
get a webber 32 36 carb.
screw into end of transmission.
look on eBay for service manual.