Body Fuse Burning Out

[Philbo]

Good afternoon guys. The body fuse on my reatta blew on my way to work this morning. I tried to replace it and instantly blew again.  Figuring I've got a short somewhere.  I did a quick search and did not find anything on the forum so sorry if repeat question.  Anyone know a likely cause? Hoping someone can point me in the right direction to save time diagnosing.  Thanks in advance.

[Padgett]

Replace the fuse with a 12v light. If on, pull fuses then relays and disconnect the alternator and starter until the light goes out.

[Ronnie]

Body (fuse #2) goes directly to splice 209 where it branches off to a lot of circuits. I think that splice is under the carpet and is prone to giving problems. I'm looking at the FSM and might come up with some suggestions for troubleshooting. Padgett gave good advice on using the 12 volt light to help isolate the problem.

[Ronnie]

1 minute ago, Ronnie said:

Body (fuse #2)

I think it is fuse #2 on a 1990. It is on my '88.

[Ronnie]

21 minutes ago, Ronnie said:

Body (fuse #2) goes directly to splice 209 where it branches off to a lot of circuits. I think that splice is under the carpet and is prone to giving problems.

I was wrong. Splice 209 isn't under the carpet as I first thought so ignore what I said above. Still looking at the FAM for a way to troubleshoot.. 

[Padgett]

Nice thing about a 12v light is that it absorbs all of the current so you cannot hurt much.

[Philbo]

1 hour ago, Padgett said:

Nice thing about a 12v light is that it absorbs all of the current so you cannot hurt much.

Looks like the same idea as these

[Philbo]

So I figured I could mimic Padgett's suggestion by just using my voltmeter plugged into the fuse slot and looking for when voltage drops to zero. Of course it is showing 12.2 or so to start.

 

Finding the wiring diagram for fuse 2 (it is #2 on the '90 as well @Ronnie)

I figured I will try eliminating this C200 connector first.

 

It is located on the passenger side down in the foot well

 

I found it and unplugged it and the reading on the volt meter dropped to zero.

 

Next is deciphering this diagram.

Edited September 28, 2022 by Philbo

[Philbo]

Except that I own a convertible and not a coupe 😜

 

This is the right diagram

[Philbo]

So I think I ruled out trunk latch by disconnecting C400 and the toneau cover switch. I am thinking it must be the splice S311, which I think is the one under the drivers seat. 

[Ronnie]

1 hour ago, Philbo said:

So I think I ruled out trunk latch by disconnecting C400 and the toneau cover switch. I am thinking it must be the splice S311, which I think is the one under the drivers seat. 

So far you are doing a great job of troubleshooting. I think you are right about S311, but if you could try disconnecting the switches and light connectors that are easy to get to first to rule one of them out being the problem. 

 

The more direct route, but a little harder, is to remove the seat and carpet and start with S311 first. When you have it apart (if it's not already rusted apart and grounding the wires right there) you can test each circuit that branches off individually to determine which one is shorted. If you find problems with the splices on that side you should go ahead and do the splices on the other side because they are probably in bad shape to.

[Philbo]

I am inclined to think that the problem is at that splice. I had those issues with water leaking in through the toneau cover. That was a good while ago that I resolved that but maybe it just took a while for the splice to degrade to the point of shorting out. The other oddity with that is that mostly the water was leaking into the passenger side, however I did have some on the driver side too. My only other thought is something in the door because I did have it apart to replace the door handle. That was a decent while ago as well though.

Edited September 28, 2022 by Philbo

[Philbo]

I am kind of confused by this portion of the diagram though. It has these turn signal relays as part of that splice 311, and yet the turn signals as well as the indicators on the dash, both still work with the fuse 2 removed. What are these? Maybe for the extra side lights that light up when you put on the turn signal?

 

[Ronnie]

28 minutes ago, Philbo said:

I am kind of confused by this portion of the diagram though. It has these turn signal relays as part of that splice 311, and yet the turn signals as well as the indicators on the dash, both still work with the fuse 2 removed. What are these?

 I don't know what they are but there is a note beside that circuit that says, "may not be present in late model convertible production". The turn signals and other items may not be powered through S311 in your convertible.

[DAVES89]

As you know the wires under the driver's side are power and under the passenger are ground. When I was having a self induced electrical problem with my 'vert we ended up pulling the carpet on both sides and redoing all the splices. Kendall [my mechanic friend who did the soldering] said he was surprised I didn't have other electrical issues. 

Always a good idea to take a look at the splices.

[Philbo]

2 hours ago, DAVES89 said:

As you know the wires under the driver's side are power and under the passenger are ground. When I was having a self induced electrical problem with my 'vert we ended up pulling the carpet on both sides and redoing all the splices. Kendall [my mechanic friend who did the soldering] said he was surprised I didn't have other electrical issues. 

Always a good idea to take a look at the splices.

That worries me

[Philbo]

Curious thing; the trunk latch will not work both from the remote, and from the key without fuse #2, but the button inside the glove box will still open it. 🤯

[Philbo]

Long time no see folks!

After just over a year, I am finally getting to trying to fix this problem.  After a good bit of pain and suffering I finally got to it.  The infamous Splice # 311.  It does look pretty suspect. 
 

[Philbo]

So still stuck on this. My soldering iron doesn't have enough "Chooch" to get a good joint, so figuring out that hurdle.  Ran out of time over the weekend and have been thwarted by too much going on yesterday and today.  Probably this coming weekend I'll have some progress.

[Philbo]

Update:

So equipped with a better soldering gun I re-did that splice as well as most of the others both under the passenger and driver's seats. There were a couple I left alone because they looked fine. The ones under the passenger seat were very bad. A couple fell apart taking the tape off.

 

Now for the bad news, fuse #2 still blows :P. The work was not for naught though as it did clear up another issue that I assumed was related to the body fuse issue, but apparently was not. 

 

That said, I'm going to cut that splice 311 back apart and troubleshoot from there. It was one of my first splices and I'm not real happy with the soldering job on it so I was kind of wanting to re-do it anyway. My technique got much better 3 or so splices in and from there I was real happy with them.

 

One lesson learned though. The wiring was pretty well tarnished. Even stripping the insulation back the wire underneath was black in most cases. One of my biggest struggles was getting the wire clean enough to take the solder. A little research online, I found a guy that works on boats (highly corrosive environment) that used muriatic acid to clean contacts. I tried it and it worked fantastic. My procedure was to dip just the tip of the stripped wire into a can with a small amount of the acid and let sit for 5 or so seconds. The wire comes out almost perfectly clean. Then dip into water with baking soda to neutralize any remaining acid, wipe dry with a paper towel and then wipe down with rubbing alcohol for a final clean. That saved my fingers from a lot of rubbing with sand paper, which is what I tried first and concluded "there has to be an easier way." Thank you Chemistry.  EDIT: Here is the youtube video I found https://youtu.be/mMF5bhbucro?si=ip5vALkUCoUKHBRC

 

 

For those interested muriatic acid is Hydrochloric acid (HCl) and can be bought at home depot as a strong concrete etcher/cleaner. It is nasty stuff so you want to follow all the precautions on the bottle for sure. Baking soda works well as a neutralizing agent. HCl does not react with copper, but reacts strongly with copper oxide. It will cause copper to corrode faster because as it reacts with the copper oxide it continuously exposes fresh copper to oxidation, so it is important to get it all off the copper after the cleaning is done.

Edited November 8, 2023 by Philbo