Catalog Ordering & Shipping Electrical Tech Work Shop Tips About M.A.D.




          The 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 140amp alternators.

          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.  

(1)    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.

(The more modern alternator with built-in voltage regulator has much better output at low RPM and idle speed, better reliability, and reduces clutter.)

This 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 method.  It’s great with a “stock” electrical system and a 63-amp alternator (“stock” model 10SI).

This 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.


Since 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 CHEVY system.

If the wiring is in good condition, and the battery will remain up front, this method is fine for many applications. 

(2)  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.)

New 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 up-grade.  The 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. 

Like 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.

This 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.) 

(3)  Use this 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 rear.

Even 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.)


 Install 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 alternator.  The new terminal block on the firewall will be maintained at about 14volts.

When 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 forward.  It’s 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.

This 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.

In 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.

Also 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 firewall. 

When 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 system.  This kit can be used with “off-the-shelf,” factory replacement alternators, such as the 94amp model 12SI DELCO.  And the kit can also be used with more powerful custom alternators.

It’s 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 firewall.  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 dash.  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.

The 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. CATALOG. 


In 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 battery.  Beginning 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!)

In 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 wiring up-grade.

The best up-grade method for improving these cars is to install the “NEW SYSTEM” which is shown in a previous diagram. 

In 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. 

Click here for the last part of this tech feature 

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