Grounds causing havoc!

FoMoCo17

Member
Apr 1, 2011
188
3
18
1990 Mustang GT 5.0, supercharged

Question #1
Last Winter went through the car and cleaned the ground circuit up and the car seemed to run much better. Recently, it has been running so bad that I had to take it off the road. Found an EVR solenoid shorted internally and has been replaced. Car ran a bit better but still terrible ... rough idle, lean codes, stalling when starting and on restarts. Anyway, I went back checked so many things and all looked good. Then, I found what I found last year 50 Ohms on Pin 20 to BAT GRND, 48 Ohms on Pin 40 to BAT GRND, and 48 Ohms on Pin 60 to BAT GRND. And, I bet once again, it is that connector next to the battery where I traced it to last year. No oxidation on connector just seems like a source of high resistance for some reason. It snaps together well etc. Does anybody know why these connectors are the source for high resistance when not corroded or anything??? Why did Ford put this in-line connector (junk) when they terminated the wire 4 inches away on the inner fender near the battery with an eyelet??? Personally, I am thinking about snipping this connector out and soldering in a solid piece of wire to eliminate this constant source of a bad ground ... any thoughts?

Question #2
Pin 20 on the 60 Pin connector is labelled as case ground. Looking at a schematic, it shows the three ignition wires leading to the TFI Module shielded with this case material. Additionally, it shows that this case ground is grounded somewhere close to the case shielding. Does anyone know how and where this case ground is and how it is attached to the case shielding and what it grounds to??? Also, is the wire leading to pin 20 just soldered to this case shield or attached in a different manner??? I had heard that Pin 20, Pin 40, and Pin 60 all ran to one wire that leads back to the battery ... is this correct???

Some insight into these questions would be much appreciated since I have not seen this covered before. Would definitely like to know that the case shield is grounded properly and not intermittently.
 
Computer power grond - pins 40 & 60 go to one wire near the windshield washer filler. Due to problems with the quick disconnect for the computer ground, I have cut it off and just used a ring terminal with the bolt near the windshield washer filler. No problems and it is an easy fix.

The ground on pin 20 is the shield ground for the foil shield wrapping for the TFI cable. It connects to ground near the computer on the floor pan. The foil shield on the TFI wiring reduces interference and prevents the ignition from messing up the radio and prevents other electrical interference from affecting the computer input from the TFI.
 
Thanks JRichker!

How is the shield attached to the wires? It appears from diagrams that the shield is attached to Pin 20 wire and then attached to a ground wire on the passenger side below the computer which you mentioned. I ask how it is attached since I wand to know if the connection is a good connection?

Yes, I removed the computer ground connector mentioned and added a length of wire with eyelet to the fender and resistance dropped like I thought.