1qwiksearchindex Quick Search

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 negative).

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 source.

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.


To headlight relay how to

DISCLAIMER; If you don't know diddly about electrical circuits, DON'T MESS WITH THEM!!! ...........................................Shasmu ' 08