Chasing a short

[PrimeMvr]

Anyone know what the black wire on this connector feeds on an 83 SC? One side is on the #4 fuse and the other heads into the factory wire loom along with a red 8, maybe 10, gauge wire behind the fuse panel.

I've determined it's hard-shorted, showing almost no resistance to ground. Thanks for your help!

[timmy2]

Rear defogger switch and fresh air blower motor. Assuming it is actually coming from fuse #12... For that size wire.
Or fuse #18 to luggage compartment light glove compartment light and a bunch of other lights if it is a thinner wire (the black one)

Hard to tell if the fuse panel is oriented correctly in the picture. Fuse 4 is for marker and turn signal lights, the numbering starts nearest the bumper.

EDIT: after looking on my computer at a full size picture it appears that the second choice is the right one... Fuse 18...
You threw me off talking about a large gauge wire... The red one...

[911pcars]

Best to obtain a wiring diagram for your MY 911. Make a copy of the diagram, then locate the black wire at fuse #4. With a high lighting pen, ID all the electrical paths from fuse #4 to ground via the branch circuits and the loads (trunk light, dome light, cig. lighter, etc.).

To isolate the offending branch, wire or load, disconnect the branch at a convenient location (e.g. remove source wire from dome light assy., Cig), then retest. If the short to ground disappears (confirm with new fuse if you wish), you have isolated the offending branch circuit. Continue testing to further isolate the section or load in the circuit to ID whether it's a pinched wire or malfunctioning load (bulb holder, motor winding or other internal short, etc.).

Hope this helps,
Sherwood

[Algernon]

Originally Posted by PrimeMvr

Anyone know what the black wire on this connector feeds on an 83 SC? One side is on the #4 fuse and the other heads into the factory wire loom along with a red 8, maybe 10, gauge wire behind the fuse panel.

I've determined it's hard-shorted, showing almost no resistance to ground. Thanks for your help!

That looks like fuse #18, always connected to battery power via 5A fuse! It goes to clock, interior lights and key buzzer. With it disconnected those should be off. Most likely interior light IMHO.

[boyt911sc]

Originally Posted by PrimeMvr

Anyone know what the black wire on this connector feeds on an 83 SC? One side is on the #4 fuse and the other heads into the factory wire loom along with a red 8, maybe 10, gauge wire behind the fuse panel.

I've determined it's hard-shorted, showing almost no resistance to ground. Thanks for your help!

Prime,

The two (2) wires coming from fuse #18 (5 amp, hot all the time) and counting from the front are:
a). Red wire......goes to OXS.
b). Black wire goes to clock, glove compartment, interior courtesy lights, key-in buzzer relay, and luggage compartment light (black/white wire).

Tony

[PrimeMvr]

Thanks everyone. The culprit was the trunk light. All fixed. Another Pelican victory

[Algernon]

Which raises the question, what is the point of the connector? Unless Porsche recognized the likelihood of spontaneous shorts to interior lighting circuits! But even then another smaller in-line fuse would make more sense!
So what harm to just remove it, and connect the black wire directly back to the fuse #18 at the panel?

[PrimeMvr]

Algernon, exactly! That's what threw me off. I thought "if there's a special connector, this wire must go to something 'special'". Ah the joys of pre-21st century german engineering.

Engineer: "it has this much hp/tq, go 0-100 this fast, pull x G's in a corner....What? You need a dome light, clock and cigarette lighter? Ah crap, what's laying in the parts bin?"