wont start

[Briguy]

Yeah the pump running will not hurt anything, the fuel pressure regulator will allow excess fuel to return to the tank.

Check the smaller ground wire that is supposed to be connected to your negative battery terminal. It should have a round connector about 6-8" down the wire and then split off into two wires... that's the ground for the ECM and fuel pump, if it's not connected or has corroded off, you will have this exact issue...seen it happen a lot.

There is a wire that's been disconnected I thought it ran the radio or something. I will double check when I get home.

 

[Briguy]

What am I supposed to be seeing here? I looked for a wire that disconnected with two wires attached but I can't find one.

 

[Curious Hound]

I think he was referring to that smallest wire coming from the negative battery terminal.

Regardless, that terminal is bad news. You have bad connections there due to corrosion. I would recommend replacing those cables. And if the positive side looks similar, replace it also. For a temporary fix, you might be able to cut an inch off those cables, re-strip them and attach with a new clamp. But that will only be a temporary solution.

 

[Shran]

Those two small wires need to be hooked up to the harness that runs along the fender... It appears that at least one of them is disconnected (the one on the right side of the pic.)

 

[Curious Hound]

Those two small wires need to be hooked up to the harness that runs along the fender... It appears that at least one of them is disconnected (the one on the right side of the pic.)

Looks like the medium-sized wire is going to the ground screw on the rad support right there where it should be.

 

[Shran]

Yeah, that one's fine, it's the other one that appears to be bare on one end and not connected to anything. It's supposed to snake down and next to the battery tray where it connects to the harness... I would bet money that's why this truck won't start unless the wire it's supposed to connect to has been grounded somewhere else (but I doubt it if the owner said it just quit... probably came un twisted and shut off right then.)

 

[Briguy]

Yeah, that one's fine, it's the other one that appears to be bare on one end and not connected to anything. It's supposed to snake down and next to the battery tray where it connects to the harness... I would bet money that's why this truck won't start unless the wire it's supposed to connect to has been grounded somewhere else (but I doubt it if the owner said it just quit... probably came un twisted and shut off right then.)

View attachment 66538

Which wires on the wiring harness? Green and black? And does the green and black run to the EEC relay?

 

[Paulos]

This wiring diagram shows a Black/light green striped ground coming off of the battery, and it supplies a ground to the ECM/ECU, EEC relay, and the O2 sensor. It looks like it's the wire that @Shran circled in the picture. I just looked at my '87, and that ground wire should go into the wire loom that is right behind the battery (it looks like where all the loose wires are in your picture). From there it probably branches off towards the intake manifold for the O2 sensor, and towards the EEC relay and beyond for the EEC relay and ECM/ECU.

 

[rang-a-stang]

On my 86, That wire is the EFI ground. I spent a day, opened up all the conduit in my engine harness, and rebuilt all my underhood grounds. Made a huge difference.

On my 86, that wire off the battery terminal met this nasty ground in the harness right next to the battery. I would think it was S124. There was another one in the harness just under the throttle body, to the passenger side. If you want to verify your grounds, pull the connector off your computer and measure pins 20, 40, and 60 to ground. They should all be less than about 3 ohms.

 

[Briguy]

That was the problem

 

[Briguy]

Yeah the pump running will not hurt anything, the fuel pressure regulator will allow excess fuel to return to the tank.

Check the smaller ground wire that is supposed to be connected to your negative battery terminal. It should have a round connector about 6-8" down the wire and then split off into two wires... that's the ground for the ECM and fuel pump, if it's not connected or has corroded off, you will have this exact issue...seen it happen a lot.

 

[Briguy]

Yeah the pump running will not hurt anything, the fuel pressure regulator will allow excess fuel to return to the tank.

Check the smaller ground wire that is supposed to be connected to your negative battery terminal. It should have a round connector about 6-8" down the wire and then split off into two wires... that's the ground for the ECM and fuel pump, if it's not connected or has corroded off, you will have this exact issue...seen it happen a lot.

That was the issue that darn ground