any manual for the 98-01 is the same chassis code is E1

 

there should be 2 relay boxes under the front seat, the one with the red connector is the fuel pump relay, the other one, i believe, is the lighting relay. been a while since i had to mess with one, but i believe its a (roughly) inch and a half by 2 inch by maybe a half inch black box .

next time it happens check and see if you lose the tail lights too. if you do, it's not the relay b/c it only controls the headlight if i remember right.

 

i do not loose tail lights. only headlights.

 

find that relay and check the electrical connection on it. you might try tapping it with a screwdriver handle too and see if your light go out, or flicker, or anything they shouldn't do. if the contacts internally in it are worn, that could be the problem.

intermitant electrical problems are the most pain in the ass things to diagnose. good luck.