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Yes, typically the headlight relay is in the underhood fusebox if one exists. I'm a bit surprised that a truck that old has one, though. It's not typical in early 80's Japanese makes. Honda started doing it in 1986 with the new Accord and in 1985 with the first EFI vehicles but I'm not as familiar with Toyota as I am with Honda.
Dig out your owner's manual; everything you need to know about fuses will be in there. If you don't have it anymore there's great coverage of your year truck in Chilton and Haynes (I've found Haynes is a bit more complete for Japanese makes).