Hi I’ve purchased the Thermo Pro 90 wiring harness 9030666a from you but don’t know how to wire it in? Any help would be greatful as to which colour wires go into positive / Negative. Thanks Matt

hello, is this for a new Webasto Thermo Pro 90 heater installation? do you have any existing wiring? Which controller do you have? Please review link to workshop manual below, circuit diagrams section 11, as a starting point and let me know what you think. A basic diagram with an ON/OFF please see attached

Battery negative is always Brown

Battery positive is generally Red

https://www.butlertechnik.com/downloads/cms/7431/webasto-thermo-pro-90-workshop-repair-service-manual.pdf