When did Ford change the 5V Ref. Voltage from Neg. to Pos. coming from pin 26 of the EEC?

I was checking a 1986 BII Code RC1 and it is Neg. 5V, checked a 1995 F150 Code HUG2 and it is Pos. 5V.

Anybody know any information on this?

Thanks

 

I cannot find anything that says the voltage switched polarity. This vref voltage is usually in reference to pin 46, signal return pin. I wonder if you get any voltage between ground and pin 46?

 

For this reference voltage to be negative, the truck would need to have a positive ground system.

Check to make sure you didn't reverse your meter leads.

Steve

 

Meter and power supply leads were not touched. This was a bench test and I just unplugged one EEC from the breakout box plug and plugged the other EEC in.

I needed the Reference voltage to be positive for my sucka to work when it is plugged into the test port on the EEC to suck the Program out of the EEC.

Being negative it would not power up the chips on the sucka.