1990 F150 Custom / 4x4 / 4.9 liter I6 300 / Manual Transmission

Water is coming into the cab near the ECU / computer and I'm wondering if anyone else has had this issue or knows how to fix it.

To be specific: If you are facing the pedals / front of the truck (from the inside of the cab), the ECU is mounted horizontally and there is a metal mount / access plate of sorts that mounts to the left side of the wall of the cab to the left of the ECU, just above the 45 degree angle of the floor. I don't think that it's the windshield leaking since water would be all over the place, but anything is possible. I opened the hood and noticed that water runs down the inner firewall of the engine well, right around where the ECU plugs into the wiring chassis. Also, water flows down "somewhere to the right of where the ECU is.

Any ideas?!

Thanks,
Nabor J