Engine 1988 GT CA MAF plug different size?

Mustang5L5 said:

I'd erase your codes, drive around a bit same run again. If code 66 returns, you really need to check MAF signal voltage at the meter, and then down at the ECU between pin 9 and 50.

Should be around 0.5 volts at idle and increase towards 5.0 v the higher you rev the engine.

Testing at the ECU will rule out a bad wiring fault somewhere between meter and ECU.

Could be a bad meter, but I'd troubleshoot and test first before firing the parts cannon at it

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Blown88GT said:

None of those caps are leaking.
Conformal coating is intact.
Conformal coating is the green tinged somewhat waxy coating over the entire circuit board assembly.
https://www.techspray.com/the-essential-guide-to-conformal-coating

Therefore, I will assume ECU is good.
I think these old ones are better than the later ones.
They were careful choosing parts & performing assembly, since it was all new to Ford & Hitachi (who designed & built much, if not all of it for Ford). You'll see Hitachi's name on the MAF sensor.
It looks like my original DA1, just about perfect. Even the port connector looks brand new.

Now I suspect a corroded connection between the MAF & ECU.
A corroded connection will cause a voltage drop, which is like adding a resistor where none is called for.
It's like a blockage in a water line to your house or what causes a heart attack in you.

BTW, I used to design & build circuit boards for the aerospace/defense industry, so in this area, I am an expert, especially old ones like this.
FYI. The 5th pic with the long "chip"with the yellow rectangle on top is the PROM (Programmable Read-Only Memory). Those were UV erasable & had a clear window on top, where you could see the real chip inside.. After they burn it with the program, they cover the clear window with paint or a sticker.

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