Get your alternator tested at autozone,its free,and check your battery too.
Check your ignition fuse,its in the fuse box,also,your fusible link could be burnt or melted,its connected to your positive battery cable,if burnt or melted,then its your problem.
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
check out ebay.
It is located on the right side below the gas cap.
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.
You might have loose connections or low cells on your battery. Check the cells on the battery and if they are low fill them with distilled water only. Also make sure your alternator is giving the battery a good charge.
get a webber 32 36 carb.