Electrical Foxbody AC System Issue!


New Member
Aug 23, 2018
I have followed Jrichker detailed steps on getting AC compressor Clutch to engage.

At WOT relay i have no power to black yellow wire.
I have 12V to Pink LT Blue as well as 12V to Red.
I Grounded the Orange LT/Blue wire with a good ground, and still didn't see 12V.
I then went and bought a new relay and still the same issue.

In simple terms:
RED: 12V
Pink/Lt Blue: 12 V
Orange/Lt Blue: 0
Black yellow: 0

I verified ground at AC Compressor Clutch as well as the I verified continuity from Black/yellow wire at relay to compressor clutch.

Info on car:
1987 Mustang, previous owner swapped an entire 1989 MAF harness in. I have installed a Fitech system. In other words the car is converted to a carb. I left the A9L in and harness to run AC. The only thing I removed was Injector harness at 10 pin connectors. I read the ground on the fire wall from the injector harness is for 02 sensors. Could removing this harness be my issue?

Any suggestions?

Thanks in advance for any help or to steer me in the right direction.
  • Sponsors(?)


Put lubricant all over the balls
Mod Dude
Feb 18, 2001
Here's the wiring diagram for an 87-89 Mustang A/C and Heater system



Ground on the injector harness is for the O2 sensors. I would torubleshoot the WOT relay a bit more. If you ground the O/LB on the relay, it should close the relay with a click and you would have continuity from the Pk/lb wire over to the bk/y wire.