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Looking for some advice on some electrical issues in my 2001 Civic EX:

As a preface, I've gone through all my fuses and checked each one. None are blown.

1. The interior lights do not come on when any door is open. Bulb in dome lights are good as I can manually turn them on. (simple checks done like making sure the dome light switch is in the middle position. Opening doors one at a time to see if the djs are bad. I'm assuming all 4 are not bad, but could be wrong) Checked voltage to the door jam switch plugs and getting 12 volts. I also do not have the reminder dinger going off as the key is in or if the headlights are left on.

2. The main door lock switch doesn't actuate any of the door locks. Checked voltage to the switch and that's good. Is there anyway to jump the switch to try and make them actuate? I haven't taken any door panels off yet to test the lock actuators, but that's probably my next move if I can't force actuate them from jumping the switch. (I do not have a remote fob to test otherwise)

3. My third brake light doesn't work, but honestly, I haven't even checked the bulb yet to see if it's blown. Plan to do that tomorrow, but adding just in case it's tied to some of the other issues.

Any help appreciated!

**Update/fix:

Replaced the multiplex unit (under dash fuse box) and it fixed the issues. Third brake light was a bad bulb and not related.

Symptoms:

• Main door lock switch did not work even though the actuators in the doors were good.
• Brake light on instrument cluster stayed on even when e-brake was lowered fully.
• Interior lights would not come on when the doors were open.
• No chime when key is left in ignition.
• No chime when headlights left on.

 
Rep Power: 244

You checked in car and under hood fuses? With a meter or visual?

 
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Thanks for the reply!

I have checked both under the hood and in-dash fuses. I have only visually inspected them, though. Are there specific fuses I should check continuity on that would relate to the multiple issues? I can go through everyone of them, but if you know specific ones to look at first, that'd be appreciated.

One further note, if it matters, the previous owner swapped computers on the car, so not sure if that would have an effect. I wouldn't think it would, but just further info in case it matters.

 
Rep Power: 367

computer should not affect any of the issues you are having

 
Rep Power: 222

Door locks are most likely either broken wires or bad actuators.

 
Rep Power: 367

the driver door usually presents damaged wires at the door hinge due to stress from opening/closing
open the door, pull the boot and check

 
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I'll pull the door panel today and check the actuator. I'm getting voltage to the main door lock switch. I thought I could jump the plug to get all locks to actuate, but that didn't seem to work. I didn't hear any of the locks try to actuate. I probably didn't jump it correctly. Either that or all actuators are dead. I'll comment again once I checked out the actuator.

 
Rep Power: 222

Since all 4 aren't working broken wires in the door jamb are more likely. Unless the previous owner ignored the actuators failing one by one

 
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Evening update: Needed to replace the window regulator/motor in the rear driver's side door. While I had it apart, I put voltage to the door lock actuator. It functioned. Also tested the rear passenger side and then the driver's door. All three actuators that I tested functioned. I pulled the boot back in the door jam and didn't see any obvious signs of breakage. While testing the lock actuator on the drivers door (Which is a PITA to get to by the way) I also attempted to test the plug above it on the actuator. I'm not entirely sure what it is for, but I couldn't get it to do anything by applying voltage. So, since 3 out of 3 actuators I tested worked, I'm assuming it's either a wire or fuse. Can anyone point me to a diagram or tell me the fuse/wires I should test? Thanks for all the help thus far.

Edit: Possible there still is a bad wire somewhere in the door jam. I couldn't get the boot back all that far to look thoroughly. From what I could see, they all looked clean and not stripped or crimped. I might end up just taking the whole door off to really get a good look.

 
Rep Power: 222

Yeah unfortunately you need to pull the door harness to examine it properly. And its harder to get at the fronts. Either pull the door or the fender.

 
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Evening update: Took the door off completely. Inspected all door jam wires and they looked good. Ohmed out every single wire from plug end to plug end with no issues. I even wiggled each wire at the jam area just in case it was an intermittent break. Nothing. Took the meter and ohmed every single fuse under the dash and under the hood. All good. At this point, the only thing I can think of is the multiplex unit is shot. Would yall recommend doing that next? (At least I'm ruling stuff out and not chasing my tail here)

Side note: I'm getting pretty good at taking door panels off on civics.

 
Rep Power: 222

Potentially it's bad, there should be a troubleshooting guide in the manual you can download here: https://www.civicforums.com/forums/1...l-updated.html go to the most recent link

 
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the multiplex is a recall item, though it is about overheating

 
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Update: It was the multiplex unit. Went to the junk yard this morning to get a few miscellaneous parts. Grabbed a multiplex unit out of an exact match vehicle. Installed and now everything is working like it should. Not bad for $30 bucks. Appreciate every one of you who helped me along the way. I'll edit my first post for an update in case someone else runs into a similar issue in the future. Thanks!

 
Rep Power: 367

glad you found the cause!

interior lights, door locks and brake light going out because of the multiplex is weird, though...

 
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Agreed. I happen to run across a random car-help post last night while googling that had the exact same symptoms and they recommended a multiplex unit as well. That person even said their A/C no longer worked, but I can't imagine that part was related.

 
Rep Power: 222

Well done