Electrical Archaeology Part III

[304065]

Ladies and Gentlemen:

While checking my charging system I had the oil pressure/oil temperature gauge out of the dash, and I was trying to find out if I had 12 volts between the blue wire (D+/61) and the red with black stripe (switched +12v). I turned the ignition key on and . . . no voltage, but plenty of smoke and a nice sizzling sound.

When the smoke cleared I found that the red wire with black stripe had melted most of its insulation, and had arced against the brown ground wires that daisy-chain across the back of the gauges. Some of the sender wires had also arced and melted together.

To make a long story short I have located a supplier for the original german brass connectors and rubber sleeves, and original german plastic-covered wire, including the correct spiral black stripe. Check out http://www.ynzyesterdaysparts.com/ for - they manufacture an RSR harness so I figured they know their stuff. I couldn't bring myself to use different wire and AMP Faston connectors- this would make future diagnosis difficult, and also serve as an acknowlegment to future generations of my ham-fistedness.

Anybody have a guess as to why the arc welding? Only thing I can think of was that I disconnected the positive lead to the trunk lights so they wouldn't bleed off battery voltage while I had the hood open to charge the batteries. But this does not appear to be in the same circuit with the lights. Maybe there was some chafed insulation somewhere.

I now look forward to removing each gauge, marking the back with a permanent marker, putting a wire marker on the wire, and then fabricating a new mini-harness for the backs of the gauges. Fortunately the heater is out of the trunk pending my fuel cell install so I can access the gauges from the back side. Anybody have any advice, other than to not do it again?

Thanks in advance,

John

[jkeyzer]

That shouldn't happen (duh). Examine the insulation very closely on all the gauges and make sure there aren't more accidents waiting to happen... Maybe as you pulled the gauge, a wire became disconnected and shorted to ground?

[Roland Kunz]

Hello

My guess is that you just had the instrument pulled out and hangend on the wires. So the possibility that a red/black rubber isolatet connector was close to earth was very high.

I fear you have to go trough the complete frontend wireloom as the wire maybe is meltet down rhe full lenght to the ignition switch and has meltet some other wires togehter witch can start making trouble a few secounds later or lurk for years untill it hits you on a wet day somwhere behind the outpost. ( OK this is a Porsche they will make it home other cars like to break down elswhere )

Refurbrishing 911 wirelooms is very simple except the rubberized connectors are hard to fix.

Grüsse