Hey guys I’m finishing the wiring on my 1990 civic with b18C engine and ran into a little confusion I have this empty plug on my thermostat and I have no more plugs.
after cross referencing to my already bswapped 1990 civic with b16 in it I noticed this plug is not there at all.

my question is can I leave this plug empty or am I going to run into problems?

Brown plug on thermostat housing

 

That's your fan switch. You need that! Also make sure the ground coming off the harness to that housing is clean and tight. Its for your ecu..

 

i found a sub harness with a relay that runs from the brown plug on thermostat to the fuse box and rad fans both ends have a ground, one on the thermostat housing and one on the fan end that goes to the clutch cable bracket with the negative terminal ground but my fans never turned on. Even when overwritten with Hondata.

my other EF has rad fans that work and the plugs wired into the main chassis harness coming out by the passenger headlight. I found the same wires (cut) on this EF . I was going to try to wire those into the rad fans hope that works.

 

Stock 1990 Civics' fan switch is at the rear of the engine block. Some other model Hondas and later Civics had the fan switch at the thermostat housing.

 

i only have the single engine oil pressure switch plug on the rear of this engine and my attempts to run the fan to the wires connected to the chassis harness failed, fans didn’t kick on. Going to try the overwrite in hondada on next attempt if that doesn’t work I have no clue what else to try. I really don’t want to resort to a manual switch