ltoolio

Chalk this one up mostly as curiosity / a desire to learn versus there being a specific problem showing up within my car:

I discovered earlier this week that I have a short somewhere that is exhibiting itself through voltage coming through a ground wire.

And it got me thinking...what happens within the car when a short like this occurs, meaning how does the car handle it?

In the case of my short and how the wires were connected, I must have a hot wire shorted into the ground cable, and that ground cable was spliced to another that went to ground. So does it just dissipate into the chassis?

Again...just curious here.

j.kenzie@sbcglobal.net

Hi Ryan,
The heat eventually dissipates int0 the chassis, but before that the smaller gauge wires get really hot. The insulation on these wires burn and you will experience acrid smoke in the area. The conductor itself may melt. A fuse may protect, but they often miss protecting aberrant current pathways.
Take care,
Dave

Mrmerlin

usually this short will make a call to Lord Lucas.
Once the call is placed a short time later, no pun intended.
The harness in question will begin to make the car smell acrid.
You may even see Lord Lucas make an appearance as he comes wafting up from the passenger floor.
In any event you will want to shut off the key and disconnect the battery ASAP.

Inspect the back of the CE panel looking for crossing wires that might have joined hands,
also look for insulation that has a different sheen to it ,
as this will indicate where Lord Lucas was escaping

James Bailey

which once again proves that electricity is SMOKE ....

Alan

Most people who complain of a short never had one - when you do you usually get blown fuses or burned wires and an obvious functional failure somewhere. What you have in this case almost certainly isn't actually a short either.

Folks with leakage issues where their battery runs down over a few days - they almost certainly don't have shorts - they have equipment staying on that shouldn't (a quite different thing). When lighting circuits are dim or other things like window & sunroof motors perform poorly it almost always isn't a short - it's closer in fact to an open circuit - caused by a contact resistance build up in switches, connectors and in some case even inside wires (think ground strap).

In your case it seems you have a ground that isn't actually grounded. Since it is presumably connected to something that wants a ground - something connected to battery power - then the ungrounded ground wire will get pulled high by the power source. So just ground it... to start with (to be safe) ground it though a 5A fuse - I think you will find it ends up at 0V and everything will be happy - if so just ground it directly. Now this likely means you have something which currently doesn't work functionally - what is it?

More commonly known in my homeland as "The Prince of Darkness"

He is rumoured to have said: "A gentleman does not motor about after dark"... quite some justification...

Alan

ltoolio

Thanks for the info, guys.

Alan - good advice about grounding the brown that's currently pulling current. I've got another ground that I know that is grounded near it, and there should be no harm in tying it to that, correct (not sure if it goes through a 5A fuse, though. Need to investigate).

As for what's not working....well, I'll let you know once I trace down where the ungrounded brown goes to. I don't recall anything jumping out at me prior to console disassembly, but I've honestly not spent a whole lot of time (yet) with the car running to definitively say.

Also - thanks for the clarification on Lord Lucas. Was a bit confused by that at first. And what's that glamour shot on Ebay from? The late '80's?

Alan

Clarification - just because you see a voltage on the wire doesn't mean there is any current flowing. I think it's very likely there is no current you could measure involved here.

Alan

UpFixenDerPorsche

And the worst of it Alan, is that circuit diagrams (well none that I've worked with) never show the circuit of a 'short'. Damned inconsiderate if you ask me.

UpFixenDerPorsche

Exactly Jim



http://forums.sohc4.net/index.php?topic=69445.0

Tommyd928

Been dealing with shorts on my car lately....here's an example. This fried -black with a purple stripe- wire starts at the rear wiper connector and goes through the loom up to the intensive washer button under the dash! What a pita to trace it! No fuse blew it just fried itself and fortunately didn't melt any other cables close to it.

Cheers,
Tom

bureau13

Are your fuses the proper value? I would have hoped a properly-rated fuse would blow before that happens...

Kiln_Red

I had a scare once with a 928 once. Fortunately, I wasn't yet in the act of driving. Terminal 30 lead backed out off the female plug for the headlight switch and grounded itself to the pod. Fried the insulation of the wire all the way to the CE panel. I don't think anyone could react faster to the sight of the smoke. I had the key off and the battery disconnected in 45 seconds or less, but the damage still merited hours of repair.

Lucas - Loose Unsoldered Connections and Splices

Alan

There are very many unfused circuits on your 928. Don't rely on fuses to save you - always disconnect the battery when working. A quick means to disconnect the battery is always a good idea.

Alan

Tommyd928

This happened before I owned the car. I'm still trying to determine what caused the short - I believe it started at the button for the intensive washer system because the wire is fried all the way to the connector for the rear windshield wiper where there is a common connection; yet the wire from the connector to the rear wiper switch is fine!

I actually came across this problem while tracing another fried wire from connector "K" of the CE panel to the buzzer relay connector of the warning system.

My car has a lot of chopped or intercepted factory wires for maybe sound systems, alarms or speaker connections.

As Alan mentioned, there definitely are a lot of unprotected circuits. It's amazing how its possible for the wires to be completely burnt.

I had to carefully cut off most of the factory cloth electrical tape to trace the wires, so I bought factory-grade Mercedes cloth tape to wrap everything back up.

The only area I didn't take the factory tape off was the center area that goes behind the evaporator/heater system. I soldered the tips of the new wire and the old damaged one and was able to pull it through the cloth tapped loom that way.

Hope to get it back together tonight,
Tom

ltoolio

I ordered a bunch of wire, of varying colors patterns & gauges, from EagleDay earlier this week in anticipation of a loom review/repair. I can see a few wires under the Pod that appear to have been fried at some point (not down to the level shown above, and none that show bare wire), but I figured better to spend some time to correct & not worry versus cross my fingers & hope things don't get worse.

Related - what do y'all use to keep the loom together once you remove the factory tape?

I've used to group some of the small bundles behind the console together, but not sure if that would scale / be best for the large size of the loom.