ECU issue

Start checking and running grounds . Battery to block, Block to firewall/Heater fan, Control box to heater fan, Also Ballast or Harness may have gone bad.

I pulled my hair out on a couple one was a ground others were wiring gone bad from heat. Space the control box off the firewall so it can cool behind it same for the regulator.

There is a factory adapter used on some models depending on where it is located. Behind the engine above the firewall is not a good place to protect it from heat. The biggest long term destroyer of electronics and wiring is heat.