As Reyedy’s commented, there is no real rule outside author’s preference.

You can write:

1. Mettez le bouton Marche-Arrêt sur la position Arrêt. (imperative)

2. Mettre le bouton Marche-Arrêt sur la position Arrêt. (active voice)

3. Le bouton Marche-Arrêt doit être sur la position Arrêt. (passive voice)

Once you select to use either 1. or 2., you should stick to it in the same documentation while 3. can be mixed with both.

The target readers might influence the choice. If the document is directed to young kids, the imperative is to be preferred as it would be more easily recognized by them.

I     In that domain, French is not astrained to explicit rules, as German is, nor to a single rule, and the choice of the voice in directives of a technical nature is yours but there are trends. Nevertheles, you might have to conform to the policy of the particular firm you work for.

The trend is to use the active voice, the imperative mood and infinitival sentences.

Use of the infinitive with value of an imperative mood

 - Visser la partie A sur la partie B (assemblage du module)
 - Construire le support du module
 - Fixer le support du module au cadre au moyen des boulons dans la pochette X

The use of the imperative is also common.

 - Vissez la partie A sur la partie B (assemblage du module)
 - Construisez le support du module
 - Fixez le support du module au cadre au moyen des boulons dans la pochette X

The passive voice is also found but rarely except in the captions of technical drawings. Avoiding when possible to use the passive voice is a directive from grammarians to keep in mind but not all cases are ruled by hard and fast rules.

 - La partie A est vissée sur la partie B (assemblage du module)
 - Construction du support du module
 - Le support du module est fixé au cadre au moyen des boulons dans la pochette X

II     The translation of "Ensure that the switch is set to the ‘off’ position" could very well be along the line of the original.

• S’assurer que l’interrupteur est en position « éteint »

Nevertheless, this can be changed.

• Faire bien attention de mettre l’interrupteur en position « éteint ».

Not a native speaker of French. In my scientific field (mechanics, mathematics) usage of passive voice is made to a certain degree but not in the same amount as in English. Bear in mind that there are in French other passive structures (with the personal pronoun on or with a pronominal verb).

When imperative is used in English, this can by conveyed by either the infinitive or the imperative mood in French.

Concerning the attitude towards passive voice by French native speakers see my question in FSE

La voix passive

I’ve asked a similar question here

https://www.question-orthographe.fr/question/emploi-de-la-voix-passive/

See the responses therein.