My 1990 Civic Si has an electrical problem that causes the idiot light for the brakes to flicker on and off . I have looked at the diagrams and there are three things that should cause the brake light to come on; Handbrake, Low Brake Fluid, Bulb test.

I checked the fluid level it is fine.

Has anyone run into this before?

 

Unplug the connectors at the brake fluid reservoir and see what happens.

 

I tried that and the light still flickered I now have the hand brake wire disconnected instead and at least so far it has not done it again but it is intermittent problem so I need to give it a few days.

 

its usually the e brake connector.

just clean the contact and ground.

 

I replaced the ICU and it solved the brake light issue but it created an issue where the right front side marker stays on all the time so I swapped it back because the side marker issue is worse than the brake light issue. I would say that this is pretty convincing proof that the problem is in the ICU. Now I just need to find a good ICU.

 

@edgeman61 I was looking at the picture you posted and comparing it to the same page in my 1990 Civic service manual and I see a difference that I was wondering if you could comment on. In the B connector your manual seems to indicate a connection at B5 where mine does not. Looking at all the pictures posted here and all the ECUs I have ever seen I have never seen a connection at B5 before. What manual is that page from? My guess is that it is an error in the manual. Do you have reason to believe it is accurate? BTW I found a working ICU so my original problem has been resolved.