Solving Annoying 5.0 SEFI Engine Surge

The "ten pin" connectors are these salt and pepper shaker looking things found at the back of 5.0L engines -between the intake manifold and firewall. These connectors are notorious for developing poor connections and causing strange EEC quirks, like idle fluctuations, check engine lights, and unexplainable diagnostic codes to be triggered. On many Mustangs there may be a dealer installed extension harnesses, making it appear as if there are a total of four of these connectors.

Bright Headlights? Add Relays

The Problem:

The stock wire headlight wiring is quite small (#18)
and it follows a serpentine-like path from the battery to the
headlight switch, down to the high/low switch and then back thru the
engine compartment to the headlights. The voltage drop along this
path is not negligible, so the lights only get maybe
9-12 volts instead of the 13-14 they should have.
You also can get flickering from the headlight thermal breaker tripping,
which eventually dies from the well known "flashing Ford headlights" syndrome.

So you changed tires and now your speedometer is off?

1. Find out how far off your speedo is (with the new tires installed)
   1. Using Milemarkers
      1. Drive on the highway for 10 miles (according to mile markers) and note how far your odometer advances. Divide the odo reading by 10 and that will tell you what percentage your speedo is off.