So the symptoms of my car are the tail lights specifically the three brake lights are stuck on unless I pull the relay. Once the car is started and still in park the instrument cluster and dashlights will not turn on until the car is put into drive. Well still in park the starter motor is still trying to start the car and is whining. Once I go from Park to drive and it passes through neutral the car shuts off and turns back on on its own but once in drive all the symptoms besides the brake lights being on are gone. I do not do electrical and I hate trying to diagnose it and probably the reason why these symptoms came about. I put a bigger horn in the car onto the stock wires took out the stock horns and I started blowing the 10 amp fuse so I thought hey I'll just put a 20 amp fuse in it and call it a day. I've had it in there for about two years but I would only honk the horn for a second or two. The other day I blew the horn at my son for about 10 seconds while the car was running and as I started driving home kind of chugged out but then drove fine and it still drives fine now once and drive. It's the 18 spot under the hood on the driver side with a 10 amp fuse that I replaced and put a 20 amp fuse in it anybody have any suggestions on to where to start I still haven't figured out how to turn my brake lights off unless I just pulled the relay.

Aathon H.

 

If the relay fixes it, it sounds like there is a short somewhere causing things to go nuts. I'd spend some time checking wire looms either under the hood or in the door jam, as well as inspecting grounds to see if there is an issue with one of those. As cars age the wire looms get brittle and the wire sheath can crack causing shorts. Hopefully someone more knowledgeable about the actual wiring diagram can chyme in with more detailed places to look - sorry I can't be more help there. Good luck - curious about what you find

 

I already inspected the wires underneath the fuse box I've checked every single fuse twice. I started checking some of the wires with a Dmm. I'm also wondering if anyone knows have a good site to get some of the wiring diagrams

 

A couple things. As the battery dies on these things strange anomalies happen. If the batter is more than 5 years old or 4 years in hot climates, I'd replace it.

After that, tell us if the brake master cylinder was worked on of replaced as it could impact brake pedal height and place the brakes in an on state all the time.

Please just pull up on the pedal and see if the light goes off.

As for the horn and fuse, it is a cardinal sin to install higher amperage fuses as they are there to protect the wires and circuitry from overload. That said, start with the above items and at the bare minimum, have the battery load tested at a reputable shop and verify it meets the needs of the vehicle.

 

The brake swhich was one of the first things I looked at. I didn't test it with a DMM but I did adjust the screw for the brake on and off. Before I adjusted it I also pulled up on the pedal to check if it turned the brake lights off. Checked....yup brake lights still on. I was also thinking maybe it could be the neutral safety switch since the car keeps trying to start when it is in park and running, then as I roll through neutral it shuts off and turns back on by the time it hits Drive. I got a brand new battery yesterday charged it all night just to be sure everything was good, put it in the car, still the same thing. So I'm just trying to figure out what could be wrong when the brake lights are stuck on, will still start in park or neutral, but when it's in park it still keeps trying to start after it already has started and is running, along with my Dash lights not turning on until the car is put in Drive do they turn on, and the starter stops turning, but the brake lights are still on? Sorry if it sounds weird for the wording I'm just really tired and using speech text. Thanks to anyone who replies with any comets

 

Unlikely but aside from the fuse issue, has anything else happened? Like water damage, rodent intrusion evidence, reversed polarity cables to battery?

I can't pull up the schematics, nor can talk to the specifics of this, but I suspect there is computer module that may or may not be the main ECU that is causing these issues.
The start sequence when the dash powers off and on, the starting sticking on, the engine turning off all point to a computer involved in start, stop, run, and that computer also powers down some of the accessories during startup.

Lets phone a friend @Jeff Lange

Jeff, TIA!

 

No it hasn't had any water damage or rodents I haven't found any burnt wires or any pops fuses. The issues started after I beeped the horn with the bigger fuse I had in it. I was thinking of maybe the ECU to and I want to figure out how to test it if there is a way possible with a DMM.

 

Im thinking the body control module (BCM) is at fault. Its in the cabin on the right side. Not sure what tests you could do though.

 

Thanks for everything im going to dig into it more today maybe post a video of what it does.

 

Generally speaking, if something is blowing a fuse, putting in a larger fuse is a recipe for disaster. Did you modify the wiring at all when you installed the horn or tap into any other location?

Jeff

 

I know, i was being careless. I just take it as a stupid should of never happened lesson learned. i used the stock horn wires and just grounded the aftermarket horn to the radiator support area. And then on the driver's side fuse box underneath the hood I unclipped the box with the four or five fuses and replace the 10 amp fuse for the horn with a 20 amp that is all I did. the 10 amp fuse would pop after 1 or 2 seconds of beeping the horn. Put in the 20 and never beeped the horn much till the other day i laid on the horn for about 5 sec. The car was running and was fine untill I got home 5 min later and went to put it in park.

 

Do you remember which fuse it was?

Jeff

 

This is a picture from Google but the same as mine.

 

Right, so that's the horn fuse, which is to be expected. My concern at this point I suppose is that there's a possibility that something got too hot in that unit that holds the fuse due to the added current and is now likely damaged/melted.

The unit that the horn fuse sits in the MPX Body ECU and it houses a few different components, including the Front Controller. MPX stands for multiplex communication bus, and is used by multiple systems on the car. Unlike a CAN bus, the MPX bus is a loop, and communication requires all of the modules to be functioning.

Here is a list of systems that are tied into this unit in some form or another:



Short of really getting into diagnosing things, I would probably suggest finding a used MPX ECU and starting with that.

Jeff

 

Thanks Jeff.... you are one knowledgeable guy. Is there a way to test that whole unit that those five fuses are in? I have taken it out when this first happened and nothing was melted or smelled/looked burnt.