Don't Cut It, Plug It!
When you need power for accessories, lights, and the like, you don't have to cut and splice connections. Ford provided female bullet plugs throughout our Mustang wiring harnesses for instrument lights, sound systems, cruise control, and more. Use these plugs for light-load accessories only. Heavy loads, like high-power sound systems and power windows, need an auxiliary electrical system with its own protection. This is a three-hole plug for instrument lights, including the radio and Rally-Pac. There are other plugs for courtesy lights and accessories. Remember, do not cut the harness when you don't have to.
A Switch In Time
While you're at it, replace the switches. Headlamp switches deteriorate with age, causing the circuit breaker to cycle your headlights off and on. Contacts in switches become pitted and useless with time. Corroded contacts create increased resistance, causing heat, and possibly starting a fire. It's also a good idea to replace all of the light bulbs, including headlamps.
The headlamp dimmer switch...
The headlamp dimmer switch plugs in like this. The plug should be on the left side of the switch when the switch is installed. Use the plastic switch protector between the switch and floorpan.
The ignition switch is an...
The ignition switch is an involved installation process. For '65-'66, there is a gang plug, then a main accessory lead or two from the center post, which is retained with a lock nut. You can add power accessories from this post. These power accessories must be protected with an inline fuse. We also suggest capping this post with an insulator to prevent short circuits.
Put the ignition switch in...
Put the ignition switch in place, then slip the escutcheon in place.
Push in and turn against the...
Push in and turn against the switch, which will lock the switch in place.
Installing the ignition lock...
Installing the ignition lock cylinder is a project all by itself. Turn the switch to "ACC" with a screwdriver, then insert a paper clip wire into the cylinder to install the lock cylinder.
The lock cylinder should click...
The lock cylinder should click into place. You will probably have to try it a couple of times before the cylinder locks.
For courtesy lamps and switches,...
For courtesy lamps and switches, each door switch completes the circuit on the power side.
Grounding occurs at the l...
Grounding occurs at the light.
The brake-light switch looks...
The brake-light switch looks like this for non-'64-1/2 Mustangs and is located on the brake-pedal linkage at the master cylinder or power-booster rod. For '64-1/2 Mustangs, the brake-light switch is a pressure switch screwed into the master cylinder.
The engine-gauge feed and...
The engine-gauge feed and headlamp harnesses are connected to join the main wiring loom to these two harnesses.
The taillight harness is installed...
The taillight harness is installed by wrapping the small plugs together in a tight bundle, then tying a length of wire to the bundle with electrical tape.
Feed the wire through the...
Feed the wire through the wheelhouse area, and grab the wire from the quarter-trim-panel area. The wire is fed to the rocker-panel area, then pulled through. The wire bundle comes out at the rocker panel.
The taillight wiring bundle...
The taillight wiring bundle is inserted into the A-pillar as shown, where it comes out behind the instrument panel.
Connect the taillight harness...
Connect the taillight harness to the main wiring loom. All wires and plugs are color-coded.
Let's wrap this one up at...
Let's wrap this one up at the instrument panel. For '65-'66, the instrument lamps and plugs are part of the main wiring loom. Install a new instrument voltage regulator (also called a voltage limiter) while you are there. Instrument-wiring color codes remain the same with Falcon-style or five-dial clusters. See your Ford shop manual for details.