Hello all I just got a 05 mcs in a trade deal. Car runs great but has a list of problems. Break lights stay on after its shut off. I've checked the harness near bc1 for the diode and can't find it. I have no Speedo or tachometer both are dead. Aside from one time that the millage,cel,and outside temp came on for a few seconds but the needles never moved. No dash lights at night. dome light dims down then flickers after the door is shut. I've tried 4 scan tools and none will connect. Any help would be great I've called the dealership and was told if I can't get my scanner to connect they won't be able to either. I've read that the Speedo is something of a super computer that tells bc1 what to-do.

 

Oof. Can't wait to hear what you traded away for this sweet project.

1. Battery health. Make sure you have a good one and it holds 12.6V resting, car off. These cars absolutely HATE low voltage.
2. Charging voltage at idle. Should be in the low to mid 14s with accessories off, no lower than high 12s with them on (headlights, AC, blower, radio etc). >15V at any engine speed = bad voltage regulator (integrated with alternator).
3. Fuses & relays. There are more than one panel.
4. Ground connections, starting at the battery terminals. There are seven of them around the car. Make sure they're clean, bright and tight. Especially the one on the upper engine mount.
6. Look for moisture. Lots of places it collects and messes with connectors, wires, leads etc. Don't forget to look for leaking coolant, which can also mess with the electrical it touches.
6. Tach and speedo clusters do go bad. Plenty of threads on here about them. I just replaced my tach; was having intermittent and erratic operation issues, would run fine for the first few miles then die, then come back to life, rinse and repeat. Also, CEL, e-brake and turn signal light would stay on when they shouldn't, sometimes even for a time after the key was removed.
7. On the brake lights, assume you mean the ones on the rear of the car and not the dash (you mentioned the speedo and tach modules were dead anyway). If that's the case after sorting the above check the brake pedal switch.

Others can weigh in as well. You'll get there.

 

It has a new battery and alternator charges at 14.5. My next step is to gut the inside and check all grounds. There was some moisture under the carpet on the passenger side. I read about the plug at the fuse box so that's one of my next stops. Just going to get a 55gal drum of dielectric grease and clean and grease ever connection I can find..

Traded a old sport bike for the mini, a new drivers door, and $600 cash. Once I get her fixed up I might keep it I find it super fun..

 

Nice score!

 

The brain box in the right footwell can have a lot of corrosion on the connectors. I think rain water comes in from the windshield seal or a sun roof drain. If your carpet was wet, I’d pull the panel off and look at that box and its connectors. Curiously, mine had corrosion and a dozen splices in the wiring that looked like a dealer repair. But mine was dry as a bone. I still redid all of those splices but to no avail.

My problems were different but were fixed by unplugging the tachometer. A certainly odd repair.

Good luck,
Peter

 

Get a bucket-full of electronic switch cleaner too.

 

The floor on the passenger side was damp but bc1 was dry and no corrosion. Still greased up all the connections. I did find a few people who found corrosion on the fuse block plug that's my next stop. It's been 85+ and 30000% humidity out as of late so I'll get to digging in to it more in the coming weeks.

 

Pulled the car into my shop the other night and started pulling the gut out. When i pulled the drivers side kick panel off I found a plug that had what looked like rust dripping from it. Unplugged it and found 4pins rotted off and nasty green crap. I then popped the other side of the plug from the bracket it was on and 4 wires fell out of there homes.

after a quick search for a new plug I came up with the all or nothing answer. Looked at a few part-outs around me all had the same issues and the plugs were just as bad or worse. So I said shrinkable connectors it is. So 38 wires and 3hrs later I have no more problems (aside from the foam under the carpet being wet).

And yes I do know that the electrical system in our cars is somewhat sensitive to resistance. I unplanned one of the few good pins from the plug and found I was removing around 1/8" - 1/4" at most and after a few calculations that comes out to around 0.0005 Ω witch I don't see causing any problems.
next step is to pull the carpet up and let it dry out. Then find someone with all black interior who likes the tan to swap with or maybe skin the plastics with carbon fiber and recover my seats..

 

That must be quite a fun bundle - but hey, good job persevering! Oh, and you need to change your oil - 40K ago.

 

Sounds like a ground issue.