I am Not a Lawyer...
But the way I read the Wi statutes you would need to either "operate" the firearm or "goes armed with a firearm", both of which seem to be specific terms or types of possesion.
Having it locked in your trunk should be all-cool as long as you do not handle it while drinking, or drugged.
941.20 Endangering safety by use of dangerous weapon.
(1) Whoever does any of the following is guilty of a Class A misdemeanor:
(a) Endangers another's safety by the negligent operation or handling of a dangerous weapon; or
941.20(1)(b) (b) Operates or goes armed with a firearm while he or she is under the influence of an intoxicant; or
(bm) Operates or goes armed with a firearm while he or she has a detectable amount of a restricted controlled substance in his or her blood. A defendant has a defense to any action under this paragraph that is based on the defendant allegedly having a detectable amount of methamphetamine, gamma-hydroxybutyric acid, or delta-9-tetrahydrocannabinol in his or her blood, if he or she proves by a preponderance of the evidence that at the time of the incident or occurrence he or she had a valid prescription for methamphetamine or one of its metabolic precursors, gamma-hydroxybutyric acid, or delta-9-tetrahydrocannabinol.
(c) Except as provided in sub. (1m), intentionally points a firearm at or toward another.
(d) While on the lands of another discharges a firearm within 100 yards of any building devoted to human occupancy situated on and attached to the lands of another without the express permission of the owner or occupant of the building. "Building" as used in this paragraph does not include any tent, bus, truck, vehicle or similar portable unit.
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Here is a link to current WI State Statutes-
https://docs.legis.wisconsin.gov/statutes/prefaces/toc. Sombody more powerful than I might want to make this link a stickypost. Criminal code starts at 900, with most firearms laws at 941.
The most important thing for you to remember is that the first thing you lose when drinking is your judgement, after that you can lose all sort of important tangible and intangible what-nots.:uhoh:
edit:Man! E6cheveron beat me to it! If this was a duel, I would be dead right now!