2, THE CHEVY MAIN POWER DISTRIBUTION SYSTEM
WIRING METHODS FOR
UPGRADING THE SYSTEM
best choice of layouts will depend upon the amount of
high-powered electrical accessories that will be added,
the condition of existing wiring, and if the battery will
be relocated to the rear or stay up front.
Three wiring methods are offered, and a diagram is
provided for the third method.
The third method provides the most significant
performance improvements, and that applies to simple cars
with 63amp alternators, or involved custom cars with
The first and
second wiring methods described below will still use the
Horn Relay buss bar for main power distribution.
And if accessories will be added (Radiator fans, or
other), main power wires to the new accessories should be
connected to the Horn Relay.
Simple method with battery up front:
We can up-grade to a “factory
style” alternator with built-in voltage regulator.
(A THREE-WIRE alternator is required, the
“ONE-WIRE will not work.)
The alternator with built-in regulator must be
wired to keep voltage-sensing at the splice.
This method lets the voltage regulator read and
adjust voltage at the splice and Horn relay area.
The system will be self-compensating for voltage
drop between the alternator and the point of main power
distribution. The alternator up-grade with this method
will behave the same as with the original factory
installed system with an external voltage regulator.
more modern alternator with built-in voltage regulator has
much better output at low RPM and idle speed, better
reliability, and reduces clutter.)
method works well when up-grading the alternator, but
limiting the gross out-put rating to a modest level.
If the original alternator output wire is in good
condition, it can be left in place with this conversion
great with a “stock” electrical system and a 63-amp
alternator (“stock” model 10SI).
method can easily be accomplished with a minimum of work
and expense. The M.A.D. Part #Alt-1 wiring kit is all that
will be needed to install this wiring layout.
NEW ACCESSORIES AT THE HORN RELAY BUSS-BAR
this layout operates like the original system, it’s very
important to note that any new accessories should get
power from the Horn Relay.
Proper voltage will be maintained at the Horn
Relay, but connecting accessories downstream from the Horn
Relay would result with lower voltage elsewhere.
In example, do not simply connect a fuel pump power
wire to ignition switched ON/OFF source at the fuse box or
dash wiring. Main
power to relays such as for fuel pump or for headlights
should connect at the Horn Relay, when using this original
the wiring is in good condition, and the battery will
remain up front, this method is fine for many
Alternate method, also with battery up front:
We can install a significantly
larger gauge size wire from the alternator to the Horn
Relay buss-bar, which can deliver more power from the
alternator to the Horn Relay buss-bar. (Although wiring
the regulator for “remote voltage-sensing” will still
be a good idea.)
8gauge Tuff-Wire is supplied with M.A.D.’s alternator
wiring kits, and the new wire will strengthen the system.
When installing the “stock,” 94amp model 12SI
alternator and powerful electric radiator fans, plus maybe
a new electronic ignition system, and a few other items, and
battery remaining up front, this is a simple and effective
new 8gauge wire is also a very good idea when the
condition of the original alternator output wire is
unknown or has obviously been patched-up.
the system above, the Horn Relay buss-bar is where we
should connect main power to headlight relays, fan relays
or other accessories.
The factory style “THREE-WIRE” alternator is
still preferred; it will still support a warning light at
the dash, it can perform remote voltage-sensing, and
better availability of replacements will be an advantage.
second method is good when installing a 78amp or 94amp,
model 12SI, DELCO alternator, and with limited accessories
connected at the Horn Relay.
(M.A.D.’s Part # ALT-1 alternator wiring kit will
provide proper wiring and instructions.
The 8gauge Tuff-Wire supplied in the kit will
handle alternator output power.)
third method when installing a more powerful alternator
and more accessories.
This method will also optimize performance with a
stock system, no additional accessories, and an ordinary
63amp model 10SI DELCO alternator.
It has advantages with the battery up front, and
it’s a “must do” when relocating the battery to the
with a simple, “stock” system and no added
accessories, this system provides remarkable improvement
to performance. And
if future work might include fans or other accessories, a
more powerful alternator, or battery relocation; then an
excellent system will already be in place.
The system is simple, and the shop work is easy
when working with parts from the M.A.D. catalog.
(See a diagram of the “NEW SYSTEM” below.)
and relocate a new power distribution buss-bar.
(M.A.D.’s Part #CN-1 is shown in the “NEW
SYSTEM” diagram.) The
firewall area is a practical location for the new
buss-bar, as it is approximately a central location in the
electrical system. A
new heavy gauge wire will be routed from the alternator
directly to the new firewall mounted buss-bar.
Remote voltage sensing can be wired from the
terminal block to the voltage regulator within the
new terminal block on the firewall will be maintained at
installing many electrical accessories and a high-powered
alternator, this new layout is often the best plan. When
connection of power for many accessories is needed, the
new terminal block on the firewall will be more convenient
than the original system as the Horn Relay was far
also the best plan when relocating the battery to the
rear, because the new power distribution will be located
between the alternator and battery, rather than forward
and off to the side at the original Horn Relay location.
method places “main power distribution” from the
alternator close to the original dash “main power-up
wire,” which comes to the engine bay from the firewall
bulkhead connector (at the brake master cylinder area).
The original wiring system only has a 12 gauge
“main power-up wire” to the dash area.
And we will see much less voltage drop in this wire
if it is shortened to about 18 inches in length, rather
than routed a few feet forward to the Horn Relay.
The dash area “main power-up wire” shown in the
NEW SYSTEM diagram is simply the original 12gauge wire,
which has been shortened and rerouted to the new terminal
block on the firewall.
the NEW SYSTEM, we have installed relays for the
headlights, which removes headlight current load from the
existing dash wiring.
The shorter dash “main power-up wire” and less
current flow through the dash with headlight relays will
certainly improve performance.
notice in the “NEW SYSTEM” diagram, that we have
routed an 8gauge wire from the new terminal block on the
firewall forward to the Horn Relay.
This option is most useful with electric radiator
fans and headlight relays.
Then the main load input of power to the relays can
come from the Horn Relay buss-bar, rather than route
individual wires forward from the terminal block on the
the battery is relocated to the trunk, we move the M.A.D.
Part # ST-1 solenoid to the trunk, increase the “battery
charging wire” to 8gauge, and re-route the battery
charging wire to the solenoid in the trunk.
(Please see more about trunk mounted battery
systems in our CATALOG page on “Trunk Mount Battery
Helper Kit, Part #TM-1 and #TM-2.”)
For less cost than a tank of 92 octane, our part
#ALT-1 alternator wiring kit will make it simple to wire a
model 10SI or 12SI alternator into the original wiring
This kit can be used with “off-the-shelf,”
factory replacement alternators, such as the 94amp model
And the kit can also be used with more powerful
a handy package for alternator up-grades with all three
methods of power distribution discussed above.
The 8gauge Tuff-Wire in the package will deliver
alternator power to the main power distribution buss-bar,
either at the Horn Relay or a new terminal block on the
And when used with a factory style three-wire
alternator with built-in voltage regulator, the wiring in
the kit will also support a factory warning light at the
See Part # ALT-1, Alternator Wiring Kit, in the
M.A.D. CATALOG section.
If the model CS-130 alternator will be added, then
our kit for the DELCO CS series of alternators will do a
good job of wiring for best performance.
The kit can be used with “off-the-shelf,”
factory replacement alternators, or custom versions of the
CS series of alternators too.
kit will wire the alternator to support the original
warning light at the dash. The original warning light will work when converting from
externally regulated alternators, and even an original GEN
light on a ’55 Chevy will be operated when wiring with
this kit. 8gauge
Tuff-Wire is included with the kit, and this heavy-duty
wire will deliver alternator output to the power
distribution “buss-bar” (either the Horn Relay, or the
new terminal block on the firewall). See Part # CS-130, Alternator Wiring Kit in the M.A.D.
NEWER THAN ’71 CHEVY
most 1972 models, Chevy introduced a major change in the
main power system. The Horn Relay was moved to the firewall, and the battery
charging wire was routed to the starter, rather than the
with 1973, the Horn Relay was moved under the dash, and
then the Horn Relay no longer served as a “buss-bar”
for main power distribution.
With 1973 and newer, a SPLICE in the wire harness
near the back of the engine served to distribute power
output from the alternator.
(Fusible Link wires were at the starter POSITIVE
cable stud, and service was awkward at this location!)
these years after 1971, the “main power-up” wires to
the dash area are shorter in length than with the early
Chevy equipped with an alternator.
But with factory splices in the wire harness, and
only 10gauge wire, the addition of a more powerful
alternator and electrical accessories will require a
best up-grade method for improving these cars is to
install the “NEW SYSTEM” which is shown in a previous
the last part of this discussion, we will analyze
performance (voltage drop) and wire over heating.
Also we will
provide recommendations for lengths and gauge sizes of the
“battery charging wire” for custom systems.
here for the last part of this tech feature