Weird electrical problem

[Olde English 5]

Here's an interesting one for you:

Whenever I turn on the rear defrost, the overhead dome lights turn on and the red "door open" indicator also turns on. It does this while all the doors are closed. Defrost works, and with the defrost off when I open a door the dome lights and indicator turn on as normal. All other electrical in the car seems to be fine.

A few months ago I had a Viper remote start installed and it was some time after that I noticed this problem. I didn't get to take the car back to the place that installed the remote start until this weekend. Supposedly the remote start is not the cause, since they said they disconnected it and the issue is still there. I have a hard time believing something like this is a coincidence after getting the remote start but I guess it's possible.

I'll have to first check to see what kind of shape my battery is in. It's the original so it's about 5 years with over 60,000 miles on it, and a bad battery can cause all kinds of electrical weirdness (it seems to crank pretty strong though).

But it seems there may be a short in the harness somewhere between the defrost circuit and one of the door switch circuits. I'm not sure when I'll have time to work on this but I was thinking of checking the door switch pins on the BCM to see which one(s) change between 0 and 12V when the defrost is turned on. Maybe that will reveal which door or harness has the issue and I'll go from there.

Of course my car is out of warranty so I should have some fun with this one (detect). Until then, any thoughts or comments?

 

[mazdadude]

I would have to agree that it sounds as if it is related to the VIPER install. It also sounds like you are on the right track to discovering the problem.

Your notion that it could be the original battery is well founded. You did not mention if the car was running when you were turning the defrost on/off ?

 

[ukulele]

That is a funny problem. Based on what you've said (and with no schems to go by) I would say it's definitely the either the VIPER unit or person that installed it in the first place might need a lesson in "cut the red wire, not the blue wire". I highly doubt it's a battery problem, especially if your car cranks up, that means it's retaining enough charge to otherwise operate normally. Sounds like 2 leads that were not meant to go together are touching. That sucks man, you get a VIPER remote start put in and next thing you know your wasting your Sunday morning checking pins and schematics instead of heading to the beach or, in my case, hitting the cycle trails. Good luck, and please post the name of the business and address of where you got this installed so we can know where not to go.

 

[Olde English 5]

I knew before I even called the place that installed the remote start that this was something they wouldn't want to be bothered with. They couldn't have spent much time on it, since they called me back not long after I dropped off the car to tell me that disconnecting the remote start didn't fix the problem.

I can't directly accuse them of screwing up the car since I don't have any proof, although conventional wisdom says they did. I could take it to a dealer or some other place and let them figure it out, but then I'd be stuck paying for it (probably a few hundred dollars) - I can't count on the remote start installer to pay for it. I'm guessing the dealer wouldn't touch the remote start anyway since it's after market.

So I guess that means I have to figure this out. I have wiring diagrams for the car which I hope are accurate, but nothing really too in depth about the Viper unit. Fortunately this is really just a minor annoyance, but I won't be satisfied as long as I know it's there.