ATF temp light comes on every time I break

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Hi forum, just bought a lovelly 1994 kzn130 which needs some love and I have just changed the engine oil, filter and air filter for starters. Weirdly since I did that the atf temp warning light now comes on every time I break. I probably do need to flush it as it's pretty black, but I think this is an electrical problem with the temp sensor. It literally goes on and off with the brake lights. Has anyone ever had this issue before, and where is the atf temp sensor anyway?