Customer complaints from non-functioning air conditioning, fuel pumps that dont
work, and smoking melted wires and relay sockets. Even fires have been evident in standard
everyday Porsches. Why? For most of us with older, pre-1990 Porsches, we need to be aware
of the electrical loads imposed by the Porsche factory that never really re-wired the
Porsche line they just kept adding each new system on top of the already cramped
and overloaded original system. Porsche owners have installed radio! tape/disc players and
amplifiers and extra disc storage drives. Then there are those improved lighting systems,
alarm systems, and radar/laser detectors, car phones, lap tops, battery chargers, etc. The
list can be extensive and that is a real problem for the older Porsche. As an example, my
1968 911 is probably one of the most modified prototypes in the world. I have changed ...
everything! One common link to every other Porsche out there is that my 911 had the
original wiring system. When the upgraded C-2 air conditioning system was installed, I
knew the wiring was stressed beyond its capacity, and the A/C wiring was upgraded then.
Last month, I wrote about the replacement of the original
starter-battery cable. That very noticeable improvement led to looking closer at the rest
of the system. I found that the factory used one cable to connect the battery to one
connection on the fuse strip. From there, power supplied to two or three other connections
on the fuse block. All of these are connected on the same side of the fuse block. These
three connections (three gang) would not run power through the fuses but would supply
three individual connections to supply power to other systems. The problem with this is in
the fuse block itself.
The fuse block uses small brass strips that are riveted to
each other and the fuse terminal. When high current loads run through these strips, they
generate heat. Heat expands each part a little bit and as one strip expands more than the
others, it moves and loosens with use and time. Severe fatigue results in smoke, melting
wire insulation, and fire. 930 Turbos with two fuel pumps, and all the warm-up gadgets on
the engine, simply over tax that system. Most of the 930s have had at least one fuse
I have removed some of the original battery feed cables that
went directly to the fuse block and I have them run directly from the battery to each of
the major power systems. The following is a simplified select few areas that can be
upgraded with a few hand tools and a wiring diagram. [Click
Here for the Wiring Diagram Figure]
Air Conditioning System 911 and 930, 1969-1989
The objective is to remove a major electrical load from an
already cramped and over stressed single fuse (~16) by redirecting direct battery power to
two independent fused supplies. Install a new two gang double fuse block Nr.
911.612.085.04 ($17.00) near the standard fuse/relay panel. Disconnect 1.5 red/green wire
at fuse #20 and attach it to new fuse block terminal #1. Install a red 4.0 cm/2 wire to
the battery + terminal. Run this wire to the new fuse block and solder the end so that the
screw that secures it to the fuse block will not work loose. Attach to the two gang
interconnected end. Install a blue 25 amp fuse in each fuse holder and install the fuse
cover. Now you have a separate circuit independent of each other. The fuse block will be
cooler and not overload the rest of the system.
Ignition and Light System 911, 1965-1969
This system always seems to be overloaded and the switch and
wires feel warm when in use. Disconnect the heavy red wire from the fuse strip. Using new
4.0 cm/2 red wire, solder the new wire to the old and securely heat shrink the connection.
Avoid crimping connectors! Run the new wire to the battery + connector and attach.
Fuel Pumps on 930 Turbo, 1977-1989, (1976 used a single pump)
Both fuel pumps take power from one fuse (#16). Install a two
gang fuse block, Nr. 911.612.085.04, near main fuse strips and run a red 3.0 cm/2 red wire
from the battery terminal directly to the new fuse terminal, at the two gang end. The two
fuel pump relay sockets for pump #1 and #2 have a red wire 2.5 cm/2 running from fuse #16
to terminal #30 of pump #2 and then run over to terminal #30 of pump socket #1. Cut the
wire running between the two pins, #30, and securely splice it by solder and good
insulation to a new 3.0 cm/2 red wire, running it to the new fuse block at #2. Be sure to
solder the wire end before installing it to the fuse block. Remove the red 2.5 cm/2 wire
from fuse #16 and run it to the new fuse block and attach it to the #1 fused terminal. #2
fuse should be a blue 25 amp, as it will still power the warm-up devises as well as the #2
fuel pump. #1 fuse can be a red 16 amp fuse.
These are a few simple upgrades that improve your reliability and safety. This upgrade
takes less time to install than to write about it!
Lee Rice writes the monthly Technical & Safety column for the
Orange Coast PCA (zone 8) Newsletter. He has
generously allowed Pelican Parts to republish these articles here for the benefit of
everyone who visits the site.