How do I fix a Bad Ground?

[pro-five-oh]

When a ground goes bad, how do you fix it???

Do you have to re wire the whole thing or just put a new crimp on the wire???

I don't believe this...I was putting a new vanity mirror (mine was all discolored) in my 83 Conti and while I reconnected the assembly into the headliner I heard a pop, a flash and all my interior lights went out.

I put a new fuse in, and it immediately blew. Disconnected the battery and tried again. So, after THREE blown fuses I realized badly I screwed up. :(

I looked in my EVTM and all failures lead to a ground near the DS door. I bet this is my problem.

PLEASE HELP!

[Richard J. Parker]

If you have a open caused by a disconnected or burnt ground wire, yes, crimp or splice a new piece on.

Sounds like your new vanity is shorted 12v to ground which blew a common fuse for the interior. First thing to do is disconnect the vanity light if you haven't do so yet. Then check the + side of it's feed wire with an ohm meter to ground with the fuse out. Make sure that wire is not shorted. Then power up the wire without the vanity. Hopefully the fuse holds. If so, find out why the vanity light is shorting it's power to ground.

If not, the real problem is a short to ground on the feed (+) wire, perhaps caused by pulling or moving around when doing the work. Normally a ground doesn't go bad because of overcurrent since the fuse and wire sizes are designed to protect the wire itself.

[pro-five-oh]

Hmm, here's my problem. The power going to the vanity is only ONE wire, it must have an internal ground somewhere.

I removed the vanity from the circuit and had installed a fuse...it blew.

Does this imply the chassis ground is blown???

[Richard J. Parker]

OK, the single wire is +12 and the vanity is grounded through the mounting screws. Probably still a short on the single +12 wire.

So do the same, pull the fuse, ohm the feed wire (which should be dead at this time), make sure you don't get a ground on that wire. Grounds going bad don't normally blow fuses and in your case it sounds like the ground is actually the metal screw to the body.

[WILLIAM SHIREY]

Electrically speaking, a circuit must be grounded for it to operate. Actually, although called a ground, it is really a common or return that carries the current back to the battery negative terminal.
A ground that is connected or not connected will not blow a fuse or cause a short. Only the plus or hot wire touching ground potential will do that.
Richard is right on in his diagnosis.
Good luck!

[pro-five-oh]

Thanks for the explanations guys, as I am not too clear on electrical theory.

I have ripped apart my car and after covering the frayed vanity power wire with electrical tape the fuse blowing problem continues. :eek:

I am tossing around the idea of pulling out the fuse box and looking for bad wires behind it. If that fails, I'll have to pull other panels off and access other lights to find the short.

The car still runs, but the Lincoln gadgets are gone. At some point I'll figure this out! tongue.gif

[WILLIAM SHIREY]

One more thought Pro:
I redid the console headliner and sun visors on my '85 Mark and now I'm wondering what you did with your vanity mirror. You don't say exactly.
The reason I'm asking is that on the Mark, if you remove the whole sun visor to work on it, you must pull the visor 'swivel arm' out of the socket in the overhead console. This arm actually carries the hot wire to the vanity mirror. If I remember correctly, it was a stranded wire and some of the strands if, out of position, could conceivably cause a short like the one you are experiencing.
I'm guessing here because I really don't know all the steps you went before the the short occured.
I would suggest retracing your steps and see which one may have caused the problem, especially if everything was working before. :cool:

[ November 05, 2001: Message edited by: WILLIAM SHIREY ]

[pro-five-oh]

Here's the scoop:

I got a new mirror (not the assembly, just the shiny part) from an 86 Conti in a junkyard and was swapping it into my car's assembly. My vanity assembly is a little different from the Mark's, as mine has the garage door opener inside the mirror assembly. Yet they should work on the same principle. I also installed a set of 86 Conti coach lights too, and they were swapped without incident. They still work after this too.

So, I unscrewed the three screws for swivel arm and--like Richard said---they are grounds. The one power wire shorted as I pushed the vanity back into the headliners. I saw the spark and realized how stupid I was for not disconnecting the battery.

After removing the headliner, I saw the wire had some small holes/pits that might have been the problem. I covered them with electrical tape, but that didn't fix the problem.

The EVTM manual for my car shows that a handful of lights, the stereo, and the tripminder computer were affected by my screw up. Yet the ground for these is shared with other components that still work. So yes, this means the chassis ground seems fine.

I am still burning fuses and I am lost. Any advice is certainly appreciated.

[Richard J. Parker]

If you are sure the power wire is ok as far as you can tell, and you have tried the fuse without the vanity, and you don't really want to pull the headliner back, I'd pull/disconnect as many loads (stereo, other lights) that are on the same fuse. Then ohm the vanity lead to ground again. Something is shorting the fuse output to ground. It could be the stereo or trip minder (either is highly unlikely)assuming it is on the same fuse, if one them fryed because of a transient voltage caused during the short. But not frigging likely.

Push come to shove, take your car to the auto electric shop on Long Point just east of Campbell named Cook's Island or Cook's Auto Electric. You won't be impressed with the place, it's a shade tree (literally) operation. But they can find it at a reasonable cost.

There are some tools to find shorts on multiwire busses like this. They put an RF signal on the wire and the signal picked up by a portable receiver reduces at the grounded point.

But I still think the problem is in the original lead, possibly somewhere under the headliner or elsewhere. If your book shows where it makes a connection into the wiring harness and you can get to it, I'd disconnect it there and try the fuse again.

One last thought about troubleshooting, don't overlook the obvious and don't assume a test you did early eliminates a problem area. So be sure that the fuse is the right size and run the basic tests over again.

[pro-five-oh]

Hmm...you are right Richard! Actually I remember that when the headliner was replaced the guys did a really bad job. The visor never worked after they screwed with it. I am gonna trace the wire down to the A-pillar and see if there is a junction of some sort. School is a bit busy now but it'll happen one of these weekends.

What is this tool that emits an RF signal to find the grounded point on a wire? Is this something I can find at Radio Shack? Sounds like a real life-saver to me! smile.gif

[MarksMark]

Hey Pro, try Mouser Electronics at www.mouser.com, (http://www.mouser.com,) or MCM electronics at www.mcmelectronics.com (http://www.mcmelectronics.com) for that tool. It's and Rf tone generator with an inductive pickup. It's neat but can be finicky at times with false indications.

[pro-five-oh]

Mark, thanks for the tip. I will have to fix this problem later, for my College studies are pounding me.

I checked the wire from the headliner and it seems fine. The circuit is still screwed, though...even without the fuse the speedo will go from MPH to KPH whenever I activate the door switch. (i.e. open the door)

This is the price we pay for keeping an old car with around 100lbs of wiring in it. Hopefully I can track an RF "tone generator" down sometime before X-mas.

Later!

[ November 12, 2001: Message edited by: pro-five-oh ]

[Icarus]

From the sounds of your last post pro-five-oh, I'd check out the harness that goes throu to the door and in the kick panel there?... get a wiring diagram and see what colors are for that circuit and start there...