Ken,
The fellow in the electrical shop knows his stuff. ;-)
ROADSTER's AND THEIR (OFTEN POOR) ELECTRICAL SYSTEMS
The biggest concern with an old roadster electrical
system is the harness.
With age, corrosion, and fatigue a 30 year old car
will show it's age in the electrical department. Even
at the time Nissan realized there were problems with
the harnesses, and kept upgrading the harness wire and
fuses. 1969 & 1970 have the most robust harnesses,
with the 8 fuse fuse box, and improvements. Of course
they also introduced some other odd 'features' at the
time (which also occurred to 510's at the same time
period).
The stock wiring will handle the 35 amp alternator fine.
I have had people tell me they run a 60 amp alternator,
with no problem. Sooner or later, a little corrosion on
a splice will catch up with all of us. Any resistance
in the harness causes heat (Power = Current squared *
Resistance). With a small 0.10 ohm resistance is almost
nothing, but at 10 Amps that is a 1V drop. Heat would
be a 10 Watt bulb. So if you keep adding more load
to the system, and a larger alternator... watch OUT!
With a 60 Amp load, that small 0.10 Ohm resistance will
now mean a 6V drop. Lights would be really dim, etc.
The Power dissipated would be 60^2 * 0.10 Ohm. 360 Watts!
Mentally think of trying to grab a 100 Watt light bulb
with your bare hands! OUCH!
If that heat is concentrated at one location, in a small
area, it will start the harness on fire. Not a good thing,
and I've "been there, done that". Having the interior fill
with black acrid smoke, and all the lights go out, at
75 mph on a twisty road is not a fun experience.
Now that I have filled you with the Horror story of bad
wiring, too many loads, too big of an alternator what
can you do?
PROBLEM AREA'S:
The original harness has four ('63-67), six ('68), or eight
('69 - '70) fuses the system. If a short occurs in the harness
between the battery and fuse box, it may melt the harness!
There were no fusible links installed on the harness when new.
It is rare for the alternator to have a dead short from the
battery power terminal to ground. When it does occur, usually
it will melt a short connection of the wiring.
The original 35 amp alternator was marginal for a stock radio, lights,
fan, and wipers. When idling at stop lights, the battery will have
to supply additional power into the system. Once back up to speed
the alternator charges the battery back up.
SOLUTIONS:
1. Clean all connectors.
Clean all exposed connections. For pig tails attaching to the frame,
remove the screw and clean the area with a little scotch brite pad.
Also the terminal. A little dab of "dielectric grease" on the metal
to metal to metal contact will prevent future corrosion.
2. Add fusible links
Add fusible links to the standard harness. I like to place one at
the alternator to the wiring harness. Second from the power lead
off the starter stud (battery connection is on the same stud). Third
is off the second power lead from the starter stud.
Rule of thumb: If the Harness wire is 12 gauge, you want to go up
two steps for the fusible link. So a 14 gauge fusible link is what
you want on the larger harness.
3. Add additional wiring to the harness, for any new loads.
I'll add an additional wire from the alternator to the battery, once again
with a fusible link inline with the wire. This does decrease the current
through the stock ammeter. With a little careful planning the current
from the alternator to battery will actually follow two paths: one
through the stock ammeter and other in more direct route. If I noticed
the ammeter would read a discharge of 25 Amps when the engine was off,
but all electrical items were one (lights, fan, wipers on a wet windshield,
and radio). After I have added the new wiring, I noticed the ammeter was
only reading 10 Amps of current. Well, it means less than half the current
is flowing through the ammeter. Fine by me, just make a note of what the
ratio is.
For the stock harness, 16 gauge fusible links are fine.
For the new wire, a nice multi-stranded 12 gauge wire from the alternator to
battery, a 14 gauge fusible link is ideal.
3. Larger Alternators should only be installed AFTER the first two
recommendations are carried out.
I've installed a 60 Amp alternator on my '68 2000. I used the smog
pump bracket, and the OEM triangle support. Lots of patience and
shims to get everything lined up. Viola... an early (externally
regulated) 280Z alternator mounted up. If the alternator pulley
is not i the same plane as the water pump and crank pulley, it
will be easy to loose a belt!
If you add a later, INTERNALLY REGULATED ALTERNATOR, there is a little
trick on those items. The two terminals are marked "S" and "L". Sense
and Lamp. The sense wire is just a connection to the battery. The
Lamp connection needs to be connected to a small lamp, or resistance,
then to +12V when the ignition is on. When first powered up, key on
engine not running, it will light up the lamp as a alternator warning.
Once the engine is running, the lamp function will turn off the light
and sense that voltage is present to "turn on" the alternator. If you hook
up the "L" wire directly to "+12V" it will damage the internal regulator.
Of humor is the fact the alternator will not work when the lamp is burned
out. No warning light when starting... no alternator output, unless the
alternator is revved high enough to "kick start" it. At 4,000 rpm it will
suddenly start working again.
I didn't mean to write such a hefty note, but will try to clean this
up and send it in to the Roadster Link.
Cheers,
Tom Walter 67 2000 SRL311-00547
Austin, TX 68 2000 SRL311-01278
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