Servo Test

Unplug 8-pin connector at amplifier. See AMPLIFIER LOCATION table under REMOVAL & INSTALLATION. Measure resistance at specified wires on harness connector. See SERVO RESISTANCE table.

SERVO RESISTANCE

Circuit		Ohms
Aerostar, Explorer & Ranger
144 (Orange/Yellow) - 145 (Gray/Black)		40-70
144 (Orange/Yellow) - 146 (White/Pink)		100-150
147 (Purple/Blue) - 149 (Brown/Green)		35,000-70,000
147 (Purple/Blue) - 148 (Yellow/Red)		15,000-35,000
148 (Yellow/Red) - 149 (Brown/Green)		15,000-35,000
Bronco, Pickup & 1991 Van
144 (Orange/Yellow) - 145 (Gray/Black)		40-125
144 (Orange/Yellow) - 146 (White/Pink)		60-190

NOTE: Resistance between circuits No. 147 and 148 should be nearly the same as resistance between circuits No. 148 and 149. If the difference is more than 5 k/ohms and vehicle has a surging problem, perform step 2).

If resistances are not correct, unplug 6-pin connector at servo. Ensure terminals are clean. Measure resistances at connector. If resistance is correct, check wiring harness and repair as necessary. If resistance is incorrect, replace servo and retest.
CAUTION: If Orange/Yellow wire is shorted to either White/Pink wire or Gray/Black wire, damage to amplifier may occur.
Disconnect servo. Start engine. Ensure vacuum to servo is at least 2.5 in. Hg. Connect circuit No. 144 (Orange/Yellow wire) of servo to positive battery terminal. Connect circuit No. 146 (White/Pink wire) of servo to ground. Momentarily connect circuit No. 145 (Gray/Black wire) of servo to ground.
Servo throttle actuator arm should pull in and engine speed should increase. The throttle should hold in that position or slowly release. When circuit No. 146 (White/Pink wire) is removed from ground, servo should release. Replace servo if it fails test.