A 1983 Nissan 4-cylinder pickup truck would not have 8 spark plugs. Four-cylinder engines have four spark plugs, one for each cylinder. There's likely a misunderstanding or a problem with the engine. You might have a miscount of the plugs, or there's a more serious issue.
To find the correct firing order, you need to check your owner's manual or a reliable Nissan repair manual specific to that year and model. The firing order isn't standardized across all 4-cylinder engines.
