Nut/bolt size for a ground?

[TripleTransAm]

Just taking a chance that someone here can save me a great deal of aggravation...

I'm looking to examine a ground that is most likely NOT properly attached, and that ground point is behind the seat on the passenger's side, buried deep. I'm hoping someone here can tell me off hand what size of nut or bolt is used to attach that ground point. This might save me the aggravation of blood loss (and potentially socket loss) as I fudge around back there with my arm down the seat back (from inside the trunk).

Background: the subwoofer on my 2nd MM doesn't work, and I narrowed it down to a oddly low supply voltage which should be 12V but hovers oddly between 5.8 and 6.3V. Embarrassingly enough, I did not click on the fact that I was measuring between the ground pin and the supply pin at the connector... if the ground is 'floating' you can't trust the voltage readings on a meter!!! So I have done my pennance (removed my engineering ring in shame for a week) and will shortly go out to measure between the supply line pin and the BODY and see if I get 12V. Likewise, I will test continuity between the ground pin and the body to see if that ground is sound. The actual ground point is behind the rear seat, a bit behind that 'hump' in the trunk. Knowing how big that nut/bolt is will save me a great deal of headaches, if someone knows this off hand.

Thanks to whoever it was that mentioned the subwoofer ground somewhere in that "quality" thread we had happening. Shortly after reading that post, I had a 'moment' akin to having the back of my head slapped hard... and I realized where I made my mistake.

[STLR FN]

It's a 8mm bolt usually green in color but might be silver since Ford is going chromium-hex free fastners. I have a bunch if you need one.

[HwyCruiser]

A couple of pics I snapped when I messed with this last spring. Should give you a general location of the ground, but might have to pull the seat for prep.

[TripleTransAm]

A couple of pics I snapped when I messed with this last spring. Should give you a general location of the ground, but might have to pull the seat for prep.

Thanks. That guy appears to be there okay. Green and black. However, it looks like I'm looking for another one that should be fastened much lower... hard to tell because the diagram shows a view from inside the car. On your second image, it looks like the green guy is fastened to a narrow strip of metal structure that is horizontal... if I am to believe the diagram, there should be a second ground and this is the one that is screwing me up.

I tried to snake my hand down between the seat and this structure but was unable to reach down enough to where the big harness should be run. So it does look like the only alternative is to remove the seats, which I will NOT do... this is going to be taken care of on Ford's nickel. I just froze half my nads off tearing up my arms trying to reach back there.... enough's enough.

Anyway, I confirmed a healthy 12V between the supply pin and the car's body. And I also confirmed no continuity between the ground pin and the car's body, so it's definitely a disconnected ground.

What the f*** is wrong with the morons at STAP when it comes to running harnesses? This black/green wire in your image appears to be the same one that was dangling loose from the driver's side of the trunk hinge area back when I picked up my 1st MM in early 2003, then there was the sliced engine harness up front, now this 2nd MM also has the misplaced harness up front and yet another ground missing in the trunk. And OASIS indicates this second MM was already in the shop for a shorting problem somewhere in the vicinity of the console shifter.

This is a quality automobile????????????

[HwyCruiser]

Make that the spring before last, oh how time flies. I don't recall another ground behind the seat, I pretty much had the whole back seat area out when I dynomatted to help tone down the Magnaflow drone. I eventually wound up replacing the factory midwoofer and amp altogether.

Funny thing is I don't even listen to the radio anymore unless I'm on a long stretch of highway. I rather like listening to the beast huff and puff around town.

Good luck at the dealer. Hopefully you won't come away with a new rattle or something worse.

[TripleTransAm]

I don't recall another ground behind the seat, I pretty much had the whole back seat area out when I dynomatted to help tone down the Magnaflow drone.

Food for thought indeed...

I had another look at the wiring diagram. It's really ambigous as to where the actual ground points are. What I see is 2 wires that should be grounded either one over the other or in very close proximity. And no clear indication as to WHICH hole in the rear structure is meant to receive the bolt.

And to make matters worse, both wires are supposed to be black/green. So I have one such wire present. Which should make it the Cd Changer ground. Unless this is not the CD Changer ground, which might be currently located elsewhere, and in fact this ground IS my desired ground, only it's been severed somewhere along the harness. And hence no continuity to the pins.

With ambiguous wiring information as this, it's no wonder the STAP droids can't figure out what goes where. I might go back outside after dinner and try to wrestle the harness around to try to find out which wire is which.

Damn, it's SO much easier to deal with the wiring in my Trans Ams... clear concise manuals and LOGICAL wire routing.

[SergntMac]

Funny thing is I don't even listen to the radio anymore unless I'm on a long stretch of highway. I rather like listening to the beast huff and puff around town.

Hell you say, JD. Same here...

http://www.mercurymarauder.net/showc...&cutoffdate=10

Can't tell you how much I spent on this crap, but it's all top drawer and I don't even turn it on anymore.

If there's no one else in the car who needs to be entertained, my Marauder is plenty of fun for me without it.

And, if the someone who's in the car can't be entertained by what entertains me without this crap, I'll be pulling up curbside at the next corner for a change in company.

This car is all the noise I need to hear...Go figure.

[HwyCruiser]

Hell you say, JD. Same here...

http://www.mercurymarauder.net/showc...&cutoffdate=10

Mac, the diamond plate is a nice touch.

TTA, don't rely on my memory though, I can't remember where the heck I put my keys half the time. Here's a link to an old post regarding the harness wiring colors when I was going through this although it sounds like you already have this info.

http://www.mercurymarauder.net/forum...08&postcount=7

[TripleTransAm]

HwyCruiser, your images were a Godsend that helped me put the factory diagrams into perspective.

As I mentioned, I dressed up again (-5C out, with a light snow) and ventured out into the trunk again. So with the memory of your images still fresh in my mind, I had no trouble identifying your black/green wire as the one I saw bolted to the structure behind the seats, about where the spare tire sits.

My idea was to find a bigger harness (from which the subwoofer ground is supposed to sprout) and tug the ***** out of it until I could come across this emerging wire. It didn't help that I essentially screwed myself by securing one of the harnesses in place which had never been secured at the factory (more on that later).

So the main difference between this session and all the others is that this time I was p*ssed as hell. My colleagues at work recognize this mode and will usually stand back because "Steve is p*ssed and he's going to start ripping ***** apart until he finds the problem once and for all". I got it from my dad. It really works, too, because I know when I hit that mode I'm a pubic hair away from finding the problem. Thanks, Dad!

So in my rage, I spotted a black/green wire out of the corner of my eye, underneath the subwoofer. Hmmm.... it emerged from a harness that eventually ended up going into the fuel tank area... shouldn't be that one, but where the heck is that one grounded? So I tugged at it, and heard a noise over at the OTHER side of the trunk where the first black/green wire was grounded (the location shown in your images above). Damn... it's the same wire, but snaked six ways from Sunday behind the metal structure behind the seats. So that confirmed I was indeed looking for another wire altogether.

So I crawled up to the metal structure as close as possible, flashlight in hand, and was about to start yanking on the harness near the first ground I saw (which I had just finished securing in place, since the factory had not). Damn. Now I was really angry, and was considering demolishing the little plastic stud that was holding the harness in place. By the grace of God, I saw a glimpse of a little green stripe... I spotted the subwoofer ground emerging from the harness! And it was still electrical-taped to the harness, heading down out of sight behind the metal structure!

So I tugged and pulled and eventually spotted yet another wrap of electrical tape (factory style) and then saw the blessed ground terminal. It had NEVER BEEN INSTALLED! It was STILL taped to the harness!

The final phase of rage took over and I separated the little black/green wire from the electrical tape with my bare hands. More cuts and bruises, but it was worth it. Now I began to calm down as the waves of satisfaction washed over me... I took out my multimeter and measured the continuity between the terminal and the ground pin on the connector. Confirmed! This was the little bass-turd (no pun intended).

So thanks to STLR FN's info about the bolt size (8mm indeed), I managed to squeeze a ratchet in between the seat back and the metal structure and carefully undid the existing ground. Not to tempt fate, I refastened the two grounds from the front, not wishing to lose this bolt altogether.

Voilà... a healthy 12 volts between the supply and ground pins at the connector, and a working subwoofer for the first time in this car's history. Unbelievable.

Here's a couple of shots outlining what happened:



Wire 1 is the wire I spotted just recently, that confirmed I was NOT in fact looking at the subwoofer ground wire. Wire 2 was magically spotted thanks to a very powerful flashlight. Without this flashlight, I never would have spotted the wire snaking out of the harness and wrapping behind the harness on the way down behind the structure. Yes, wire 1 does in fact go UP, then over the structure and back down again below the gas tank level somewhere mid photo, and then back up again (where the arrow is pointing) and to the ground point. Efficient routing indeed.



This shot shows a closeup of the final grounding-from-the-front (or back, technically speaking) and I shaded in an approximate idea of how the subwoofer ground was originally routed, along with the electrical tape keeping it in place.

Success...


So, this makes TWO cars in a row with missing grounds in the trunk area, and misrouted engine bay harnesses. So HwyCruiser, I owe you a beverage of your choice should we come face to face one of these days, and STLR FN I owe you one as well for simplifying my choice of sockets to use (would have been hell to fudge around back there trying to figure out the right socket).

And most of all, I dedicate this post to the men and women in charge of the wiring at STAP... no doubt they are at this moment sharing a quiet evening a home trying to figure out how to plug in their christmas tree lights. (hint: the pronged end goes in the wall...)

[HwyCruiser]

Great to hear you solved the STAP riddle hidden in your car Steve. Glad I could help. I would have cut the damn wire and found a convenient place to sheet metal screw it down as step #2 but I guess that's the difference between and engineer and a field tech, lol.

Good job at saving a red-line and avoiding a trip to the dealer.

[STLR FN]

Think maybe I should go check mine out.

Anyhow I'm just glad I could help Steve.