sgauvry Posted March 24, 2018 Author Share Posted March 24, 2018 Try as I might, I could not find an accurate reference to the connector for the tank switch, but it exists in all trucks. On the dual tank trucks, there is a switch in with the heater controls, on single tank trucks, the switch is omitted, but the connector still exists near the heater control. There is a description of the 6 pin plug in the top corner of p.104 in the EVTM, but no references to connector number. The plug that replaces the switch has two jumpers on it. There are two rows of 3 pins. The middle position will be jumpered to either the front or rear tank wiring. If the plug is missing, your in tank pump will not run and the fuel gauge will read empty. This is also a handy place to check for voltage to your in tank pump although it would not rule out a problem between the plug and the tank itself. I also have had trouble with the fuel tank connectors. The connector body locking ears typically break off, resulting in an intermittent connection to the in tank pump and gauge sender. I sourced a replacement from Napa, but they are getting a little harder to find these days. Thanks for your work, Ray! You too, Gary and Bill! I pulled the tank pump just to give it a look-see (easily accessible due to my hatcbh built into the wooden bed). The pump is only a couple of years old. Couldn't see anything unusual there, but when I put it back in I no longer had a fuel gauge reading of full. In fact it read empty. That tells me the float was likely stuck in the full position. I am befuddled by how the fuel gauge gave me accurate readings prior to pulling my old engine and now, zippo! :nabble_anim_confused:I know that tends to happen when one pulls things apart, but this really boggles me since I didn't mess with any of the wiring that leads to the tank. I think it is possible since there was fuel in the lines before I removed my old engine, the HP pump was working alone and the in-tank pump never worked except to give me an accurate fuel gauge reading. I'm looking at page 104. That references a 2 tank system. I'm not seeing the switch you are referring to. On page 103, the single tank setup, I see no switch there except for the inertia switch. I played with that a little but couldn't seem to get it to go anything. I was expecting to get kind of a reaction like you'd get on a GFI electrical switch. Page 100 shows the fuel tank selector switch. Is that the 6 pin plug you are referring to? How the heck do you get to it. And, since my fuel gauge worked, could that selector switch be my problem? Sorry for the long post. Just trying hard to figure this thing out. Can't do any more today as my body is quitting on me. But I can read your reply when you have time. Thanks a bunch! Steve Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 24, 2018 Share Posted March 24, 2018 Try as I might, I could not find an accurate reference to the connector for the tank switch, but it exists in all trucks. On the dual tank trucks, there is a switch in with the heater controls, on single tank trucks, the switch is omitted, but the connector still exists near the heater control. There is a description of the 6 pin plug in the top corner of p.104 in the EVTM, but no references to connector number. The plug that replaces the switch has two jumpers on it. There are two rows of 3 pins. The middle position will be jumpered to either the front or rear tank wiring. If the plug is missing, your in tank pump will not run and the fuel gauge will read empty. This is also a handy place to check for voltage to your in tank pump although it would not rule out a problem between the plug and the tank itself. I also have had trouble with the fuel tank connectors. The connector body locking ears typically break off, resulting in an intermittent connection to the in tank pump and gauge sender. I sourced a replacement from Napa, but they are getting a little harder to find these days. I was able to get mine from RockAuto in Dorman's repair parts line. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 24, 2018 Share Posted March 24, 2018 Thanks for your work, Ray! You too, Gary and Bill! I pulled the tank pump just to give it a look-see (easily accessible due to my hatcbh built into the wooden bed). The pump is only a couple of years old. Couldn't see anything unusual there, but when I put it back in I no longer had a fuel gauge reading of full. In fact it read empty. That tells me the float was likely stuck in the full position. I am befuddled by how the fuel gauge gave me accurate readings prior to pulling my old engine and now, zippo! :nabble_anim_confused:I know that tends to happen when one pulls things apart, but this really boggles me since I didn't mess with any of the wiring that leads to the tank. I think it is possible since there was fuel in the lines before I removed my old engine, the HP pump was working alone and the in-tank pump never worked except to give me an accurate fuel gauge reading. I'm looking at page 104. That references a 2 tank system. I'm not seeing the switch you are referring to. On page 103, the single tank setup, I see no switch there except for the inertia switch. I played with that a little but couldn't seem to get it to go anything. I was expecting to get kind of a reaction like you'd get on a GFI electrical switch. Page 100 shows the fuel tank selector switch. Is that the 6 pin plug you are referring to? How the heck do you get to it. And, since my fuel gauge worked, could that selector switch be my problem? Sorry for the long post. Just trying hard to figure this thing out. Can't do any more today as my body is quitting on me. But I can read your reply when you have time. Thanks a bunch! Steve Steve, if you look at what I posted earlier, that was the 1985 EFI pump system with the single tank. The inertia switch, which I take it you found, is typically on the heater ducting right side of center. I doubt your problem is the inertia switch, if it was bad, the high pressure pump would not run. The pumps are wired in parallel like headlights. The problem must exist in the wiring to and from the in-tank unit. For reference in looking at the diagrams C is a connector and S is a splice. I have seen some very funky splices after 30+ years, considering I am dealing with similar vintage Chrysler stuff. At least Ford, (a) numbers connectors and splices and (b) sticks to pretty much the same circuit numbers and colors (or should it be colours) from year to year. Does the 1985 EVTM show locations? I know the 1986 one is real good about pictures of locations. Link to comment Share on other sites More sharing options...
NotEnoughTrucks Posted March 24, 2018 Share Posted March 24, 2018 Thanks for your work, Ray! You too, Gary and Bill! I pulled the tank pump just to give it a look-see (easily accessible due to my hatcbh built into the wooden bed). The pump is only a couple of years old. Couldn't see anything unusual there, but when I put it back in I no longer had a fuel gauge reading of full. In fact it read empty. That tells me the float was likely stuck in the full position. I am befuddled by how the fuel gauge gave me accurate readings prior to pulling my old engine and now, zippo! :nabble_anim_confused:I know that tends to happen when one pulls things apart, but this really boggles me since I didn't mess with any of the wiring that leads to the tank. I think it is possible since there was fuel in the lines before I removed my old engine, the HP pump was working alone and the in-tank pump never worked except to give me an accurate fuel gauge reading. I'm looking at page 104. That references a 2 tank system. I'm not seeing the switch you are referring to. On page 103, the single tank setup, I see no switch there except for the inertia switch. I played with that a little but couldn't seem to get it to go anything. I was expecting to get kind of a reaction like you'd get on a GFI electrical switch. Page 100 shows the fuel tank selector switch. Is that the 6 pin plug you are referring to? How the heck do you get to it. And, since my fuel gauge worked, could that selector switch be my problem? Sorry for the long post. Just trying hard to figure this thing out. Can't do any more today as my body is quitting on me. But I can read your reply when you have time. Thanks a bunch! Steve I'm referring to the greyed reference box labelled "fuel tank selector switch terminals" directly below the header line on p.104. (left side). Sorry, but my screenshot skills don't seem to cut it here. The switch, of course is in the blue shaded box labelled "fuel tank selector switch". The two pole switch handles the fuel pump voltage on one pole and the fuel level gauge signal on the other. Of course, a single tank truck does not have or need the switch, but the circuits are still in the cab wiring harness, hence the jumper plug. The drawing on p.103 for single tank is somewhat vague about the routing, but the dual tank drawing does seem to show a connection at C127. The circuit is #787 (PK/BK). I think the connections in the cab assume the front tank and the circuit changes to #786 ® at the switch. If the wire at your tank is PK/BK like the single tank drawing, I would assume the single tank chassis harness continues the wire color for #787. If the full dual tank wiring was in place, the chassis harness would have a R wire at the tank, (#786) and an unused connector at the rear tank location. Still, all this was unmolested when you took the engine out and it is somewhat baffling that the tank pump now does not run. Link to comment Share on other sites More sharing options...
sgauvry Posted March 24, 2018 Author Share Posted March 24, 2018 I'm referring to the greyed reference box labelled "fuel tank selector switch terminals" directly below the header line on p.104. (left side). Sorry, but my screenshot skills don't seem to cut it here. The switch, of course is in the blue shaded box labelled "fuel tank selector switch". The two pole switch handles the fuel pump voltage on one pole and the fuel level gauge signal on the other. Of course, a single tank truck does not have or need the switch, but the circuits are still in the cab wiring harness, hence the jumper plug. The drawing on p.103 for single tank is somewhat vague about the routing, but the dual tank drawing does seem to show a connection at C127. The circuit is #787 (PK/BK). I think the connections in the cab assume the front tank and the circuit changes to #786 ® at the switch. If the wire at your tank is PK/BK like the single tank drawing, I would assume the single tank chassis harness continues the wire color for #787. If the full dual tank wiring was in place, the chassis harness would have a R wire at the tank, (#786) and an unused connector at the rear tank location. Still, all this was unmolested when you took the engine out and it is somewhat baffling that the tank pump now does not run. Ray- I think our pages are different. Here's a pic of mine. I don't see the grey-shaded box you are referring to. However, what I see confirms your explanation of the circuit and wiring. Page 103, the one I've been referencing, indicates the pk/bk h wire running from the fuel pump relay down to just past C120 and then continues south to the in-line fuel pump, but also veers left a runs to the in-tank fuel pump. Although the diagram doesn't show any symbols indicating it is a splice, it must be. This diagram is more to what my system looks like. But, there are four wires that run to the in-tank fuel pump connector. One is the p/bl H wire. There are three other wires and those match the wire colors for the two tank system. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 24, 2018 Share Posted March 24, 2018 I'm referring to the greyed reference box labelled "fuel tank selector switch terminals" directly below the header line on p.104. (left side). Sorry, but my screenshot skills don't seem to cut it here. The switch, of course is in the blue shaded box labelled "fuel tank selector switch". The two pole switch handles the fuel pump voltage on one pole and the fuel level gauge signal on the other. Of course, a single tank truck does not have or need the switch, but the circuits are still in the cab wiring harness, hence the jumper plug. The drawing on p.103 for single tank is somewhat vague about the routing, but the dual tank drawing does seem to show a connection at C127. The circuit is #787 (PK/BK). I think the connections in the cab assume the front tank and the circuit changes to #786 ® at the switch. If the wire at your tank is PK/BK like the single tank drawing, I would assume the single tank chassis harness continues the wire color for #787. If the full dual tank wiring was in place, the chassis harness would have a R wire at the tank, (#786) and an unused connector at the rear tank location. Still, all this was unmolested when you took the engine out and it is somewhat baffling that the tank pump now does not run. Ray, from looking at my diagrams, C120 is the connection going to the pumps, if there are dual tanks, it shows a pigtail between C119 (inertia switch) and C120 (pumps feed) that goes back to the tank selector switch and from there to the tank units. What I am seeing, and the 1985.5 may have actually been different because it shows the 6 port motorized valve like the hot fuel package 460s used. The 1986 shows essentially the exact same system for a single tank, only the resistance wire is not used on the F-series. On the dual tank 1986 EFI the tank selector switch is shown as an added section in the harness with one end being at C120, the other becomes C127 to feed the high pressure pump. The selector switch then powers either of the in-tank pumps and connects the respective gauge sender at the same time. Does the 1985 EVTM give locations, or are you using the 1986 one? Link to comment Share on other sites More sharing options...
sgauvry Posted March 24, 2018 Author Share Posted March 24, 2018 Ray, from looking at my diagrams, C120 is the connection going to the pumps, if there are dual tanks, it shows a pigtail between C119 (inertia switch) and C120 (pumps feed) that goes back to the tank selector switch and from there to the tank units. What I am seeing, and the 1985.5 may have actually been different because it shows the 6 port motorized valve like the hot fuel package 460s used. The 1986 shows essentially the exact same system for a single tank, only the resistance wire is not used on the F-series. On the dual tank 1986 EFI the tank selector switch is shown as an added section in the harness with one end being at C120, the other becomes C127 to feed the high pressure pump. The selector switch then powers either of the in-tank pumps and connects the respective gauge sender at the same time. Does the 1985 EVTM give locations, or are you using the 1986 one? Guys - Just saw the setup for the 7.5 engine. That's the diagram my system follows, except there's a high pressure pump in mine and the C120 connector doesn't show! Weird... Link to comment Share on other sites More sharing options...
NotEnoughTrucks Posted March 25, 2018 Share Posted March 25, 2018 Ray, from looking at my diagrams, C120 is the connection going to the pumps, if there are dual tanks, it shows a pigtail between C119 (inertia switch) and C120 (pumps feed) that goes back to the tank selector switch and from there to the tank units. What I am seeing, and the 1985.5 may have actually been different because it shows the 6 port motorized valve like the hot fuel package 460s used. The 1986 shows essentially the exact same system for a single tank, only the resistance wire is not used on the F-series. On the dual tank 1986 EFI the tank selector switch is shown as an added section in the harness with one end being at C120, the other becomes C127 to feed the high pressure pump. The selector switch then powers either of the in-tank pumps and connects the respective gauge sender at the same time. Does the 1985 EVTM give locations, or are you using the 1986 one? Working off the link to the 86 EVTM on this site. Same one Gary quoted earlier. http://www.garysgaragemahal.com/electric-fuel-pump-control.html Looks like there are some differences ? Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 25, 2018 Share Posted March 25, 2018 Working off the link to the 86 EVTM on this site. Same one Gary quoted earlier. http://www.garysgaragemahal.com/electric-fuel-pump-control.html Looks like there are some differences ? Yes, and I am not sure there wasn't an update to the 1985 EVTM as I don't ever recall seeing a 1985.5 without either the 4 or 6 port reservoir or reservoir tank selector valve unit right behind the high pressure pump. Link to comment Share on other sites More sharing options...
sgauvry Posted March 25, 2018 Author Share Posted March 25, 2018 Yes, and I am not sure there wasn't an update to the 1985 EVTM as I don't ever recall seeing a 1985.5 without either the 4 or 6 port reservoir or reservoir tank selector valve unit right behind the high pressure pump. Gents - Found one wiring problem so far. Connector 127, located on the drivers side near the firewall, illustrated on page 97, Figure 1, is faulty. The y/w wire had come completely disconnected from the connecter and the black ground wire nearly disconnected. The y/w wire runs to the fuel gauge and tank sending unit, as does the black wire, explaining why my fuel gauge would not give me a reading any longer. I disconnected the battery, exposed a little wire and shoved it into the connector, reconnected the battery and it did in fact give me a fuel level report. I'll be resoldering wires to the connector once I purchase a new soldering iron. Mine has gone bad on me for some reason, after only using it a few times. Cheapo Chinese crapola! At worse, I'll bypass the connector and join the wires together because there's incredibly little wire and space to work with, so it won't be that easily accomplished. I can only hope the wire fix for the fuel sending unit is that simple to repair. Steve Link to comment Share on other sites More sharing options...
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