Last week I attempted to install a brighter LED bulb in my dome light housing .. ended up blowing a fuse in the passenger side fuse box. I replaced it and noticed that all my gauge cluster/climate controls/stereo lights refused to come on once the sun set and I turned my headlights on. Fearing I somehow blew my Multiplex Control Unit, I had it diagnosed at a shop in town - MCU was somehow fried. Anyways, I found one at a junk yard and installed - problem solved, however my dome light now stays on constantly when in the "door" position. I can turn it off and on manually but when in "door" mode, it refuses to dim and turn off as its supposed to. Anyone else have this happen to them or have a solution?

 

Well, it must not be a 1984 Accord because those don't have MICUs... just kidding. So what kind of car?

Any warning lights for "door open"? Typically, the door switches will ground the wire when the door is open. So a wire that's pinched or rubbed bare & shorting to ground would do that to the interior lighting. But it should show the door-open warning also.

 

..forgot to mention the year haha, 1998 EX sedan.
Door switches work perfectly, indicated the door is open when open on the dash, doors courtesy light come on and go off as they should but for some reason that damn dome light won’t respond. It’s worth mentioning that it’s quite dim even though it’s constantly lit. When I switch it to ‘on’ it’s very bright. Just seems to be having trouble in ‘door’ mode.

I grabbed a switch from a 98 EX in the junk yard and will be trying it out when I’m off work here in an hour but I doubt that will correct anything as it’s nothing more than a copper connection (no physical damage to my current one) but we’ll see!

 

To rule out an issue with the door switches, you can just disconnect them individually.

If it is not due to the door switches, the cause may be due to a faulty passenger side multiplex control unit or a short to ground that was caused during the initial install of the LED bulb. Since it sounds like you already replaced the drivers side MCU, that probably is not the cause.

The following is some info. from a different thread I previously responded to.

EX is slightly different than DX and LX trim.

The ceiling light (aka dome light) have dual functionality; (1) turns on if manually switched to ON, or (2) turns on if door opened. Because the ceiling light have "dual functionality" there are two separate ground sources involved in the circuit. (1) When ceiling light is switched to ON, the light switch get its ground source from the base of the unit. (2) If a door is opened, the light switch gets the ground source from the door switches via wiring that goes through the Passenger side MultiplexControl Unit (MCU) located at the passenger side fuse/relay box and onward to the ceiling light. – All the individual doors switches (at each door) are wired into the passenger MCU.

LX and DX trim levels: All the individual doors switches (at each door) are wired directly into passenger MCU.

EX trim level: Driver's door switch and left rear door switch are wired into driver side MCU (located in driver side dash fuse/relay box), then run through a pink communications wire between the driver and passenger MCUs. However, the ground will still then be running from the passenger side MCU to the ceiling light. Passenger front and right rear door switchesare wired directly into passenger MCU.