Easy* electrical improvements via relay
installation...Part one: Horn Relay
#2 How to : Relay install for brighter lights .
The 1964 1/2 Mustang wiring design differs
from all other years due to the inclusion of a relay to provide power to the horns.
In my experience, this design is superior because incorporating a relay has less
voltage drop than later models without one. The relay is basically a switch that
is energized from a remote location, in this case , the horn button. Relatively little
amperage is necessary to signal a relay to apply current to the desired component.
Starting with the 1965 models, power fed to the horns begins at main source (battery
positive), continues through the wire loom across the radiator support panel , up
the l.h. inner fender panel, to the plug located at the firewall. After the plug,
the wire proceeds to the head light switch, where it splits to power other circuits.
Other circuits fed from the headlight switch includes brake lights, horns, instrument
and courtesy lights and ignition switch. After leaving the headlight switch, the
horn power wire comes to the turn signal switch plug, through the column to the steering
wheel slider ring contacts to the horn ring contact switch before heading on it's
return path all the way back to the horns, where it finally meets the ground (battery
Because of the electricity's long and arduous journey, many amps are lost through
resistance, with this loss, coupled with corrosion of the horns often the weak electrical
signal tends to sound more like a sick cow than the harmonious chord of "F"
to which the horns are tuned. Checking for excessive resistance in switches and a
little circuit tracing can alleviate all malfunctions in many instances!
To test operation of horns, run a jumper wire to the battery positive terminal
with the horn grounded, a sound should be heard. If the horn gives you the silent
treatment, try tapping on it with a screwdriver or hammer handle. The vibration can
sometimes cause the diaphragm to begin its oscillations, burning corrosion from the
contact points thereby producing sound. Tone quality can be adjusted by turning the
screw. To avoid distorting contacts, begin adjustment by loosening screw first, then
carefully turn back in in small increments. Contact cleaner will sometimes help clean
corrosion from internal contact points.
For those times where all systems are proper, yet resistance proves to be excessive,
the relay can save the day!
The relays small size lends itself well to mounting in hidden locations, preferably
near both the battery and horns (radiator or grill area). Plan out your wire routing
for convenience as well as efficiency.
Once the 10 amp relay is mounted, connect a 12 gauge (or larger) wire from the
relay's "Batt" terminal to the starter solenoid positive pole (or battery).
To protect against any possible mishaps, include a 10 amp fuse in this line. All
connections should be crimped, soldered, or both. Heat shrinkable wire insulation
tubes are excellent for soldered or exposed wires. Neatness counts when it comes
to wiring !
Cut the wire leading to the horns leaving enough of a pig-tail to run to relay,
attach power lead from horn switch to "switch'' terminal of relay.
Using existing wire ends at horns, construct a "Y" lead to run to the
relay " accessories" terminal. The only wire remaining should be the negative,
or ground which is commonly connected to a mounting screw or another clean ground
Test your horns as they emit a sound that will be music
to your ears!!
As always, read instructions and have a good understanding as to operation
and wiring fundamentals BEFORE attempting ANY wiring alteration . Remember, slip
shod amature modifications can harbor nests of gremlins that conspire
to instigate emanate disaster.
If you don't know diddly about electrical circuits, DON'T MESS WITH THEM!!! ...........................................Shasmu