Greeting Russell. My understanding of the Mercury Mark 25E is that it was only a 2 year production for that model offering electric start, 1955 and 1956. The 1955 model had a unique “swing away electric starter”, and was positive ground, the 1956 had a Bosch electric starter and was negative ground. The control box with the wiring harness that was used on the Mark 25E also fit the Mercury Mark 30E.