Green’s Dictionary of Slang

(N.Z.) mad, insane.

1950		H. Beattie Far Famed Fiordland 85: Old ‘Arawata Bill’, like so many men who spend many years in solitude, went quite ‘wampy’ in the end [DNZE].
1975		K. Smithyman 11 Jan. postcard DNZE (1998) 888/2: He must have been wampy (or wampo) [i.e. mad] .