Machspeed Posted March 4, 2021 Share Posted March 4, 2021 I've got a good part of my dash out and while I have it out I've got to figure out why my fuel gauge is not working. I think it may be a ground issue but not for certain. A few years back when I painted the truck, I pulled the bed and replaced the floats in both tanks, as the gauge was not working then. It's been awhile and things are a little foggy in my recollection but it seems that I recall grounding the float assembly with a piece of wire and moving the float assembly and watching the fuel gauge move. Thinking I fixed it, I put it all back together to later realize that, in fact, I did not fix it. That gauge lays on empty and never moves. This is the same with both tanks....no reading either tank. No problem switching tanks though. Interestingly, just a few months ago, I happen to look down and noted that my gauge was on a quarter tank. First time I'd seen it off the E in years. Didn't last long before it dropped back down to E. This of course makes me think again that I have a ground issue. I pulled my radio yesterday as there is supposedly a ground back behind it. I've still not found it and thinking it may be down lower, perhaps below the HVAC control unit. Also, it appears I have a firewall pad back there that may also be obstructing my view of it. Regardless, I read somewhere that there is a grounding stud that runs through the firewall. The ground wire for my fuel gauge is attached to this stud on the cab side. Same stud runs through to the engine bay side where there is supposedly a ground wire that should run from this stud to the engine. I've attached a picture of said stud. Can anyone confirm this for me? Is there suppose to be a ground off this stud to my engine? Aside from my fuel gauge, I don't have any other electrical problems. Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 4, 2021 Share Posted March 4, 2021 No, I don't think that is a ground stud on both sides. I think that is one of the HVAC bolts. My remembrance is that the engine side ground goes to a screw by the windshield wiper, but we have a page on that (Documentation/Electrical/Grounds/Engine To Firewall Ground) and it differs a bit from my memory. And on the inside I think G701 is just a screw going into the firewall. But, let's talk about your fuel gauge because if everything else works it is not likely to be G701 that's the problem. There's a troubleshooting procedure in the EVTM, but if you ground the wire from the sender at the tank the gauge should slowly go past Full. If it doesn't, then you need to move your testing back to the Fuel Tank Selector Switch. If you can get on the Y/W wire coming out of the switch then the gauge should go to Full. If so, then try to get on the DB/Y and put the switch in Front and the gauge should go to Full. If not then the switch appears to be bad. If so, then you need to check C127, which is a gray 4-pin connector sorta under the master cylinder. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 4, 2021 Share Posted March 4, 2021 That is the dash support stay. The ground stud is up just beneath the wiper motor and would ground to an intake manifold bolt between #7 & 8 cylinders. Doesn't power pass through the ICVR, through the gauge, through the sender, to ground? While I suppose you could bring ground all the way back to the firewall, ground (should be) ground. A reference to zero potential throughout the system. Link to comment Share on other sites More sharing options...
Rembrant Posted March 4, 2021 Share Posted March 4, 2021 I've attached a picture of said stud. Can anyone confirm this for me? Is there suppose to be a ground off this stud to my engine? That stud is just bare, no ground attached. The engine ground attaches to the firewall just below the throttle cable and next to the large black oval plug. See below. It is attached to the firewall with a hex head sheet metal screw. PS: Depending on the year of your truck, you may not have the large black oval plug. On the feedback carb and EFI trucks, the main harness passes through this hole. The earlier trucks had no hole there at all. My '84 is DSII, so just a plug. My '80 has no hole there. Link to comment Share on other sites More sharing options...
Machspeed Posted March 4, 2021 Author Share Posted March 4, 2021 I've attached a picture of said stud. Can anyone confirm this for me? Is there suppose to be a ground off this stud to my engine? That stud is just bare, no ground attached. The engine ground attaches to the firewall just below the throttle cable and next to the large black oval plug. See below. It is attached to the firewall with a hex head sheet metal screw. PS: Depending on the year of your truck, you may not have the large black oval plug. On the feedback carb and EFI trucks, the main harness passes through this hole. The earlier trucks had no hole there at all. My '84 is DSII, so just a plug. My '80 has no hole there. Thank you gentlemen, this helps a lot. Link to comment Share on other sites More sharing options...
kramttocs Posted March 4, 2021 Share Posted March 4, 2021 That is the dash support stay. The ground stud is up just beneath the wiper motor and would ground to an intake manifold bolt between #7 & 8 cylinders. Doesn't power pass through the ICVR, through the gauge, through the sender, to ground? While I suppose you could bring ground all the way back to the firewall, ground (should be) ground. A reference to zero potential throughout the system. Jim is right - that's the bolt for right hand side lower dash support arm. G701/G106 screws to the dash support just to the right of the radio. That bolt (lower dash support arm) is what I used to beef my ground path up. Ran a heavy (2 or 4awg, can't recall at the moment) cable from the battery to that bolt. Then on the interior side I ran a cable from the same bolt to a ground bar behind the dash. From there I ran a 10awg wire to the dash support. The ground bar could be ignored and a wire ran directly from the interior side of the bolt to G701/G106. Not a modification that's really needed for most but if adding things like an amp, it's an easy way to add a reliable ground path. Link to comment Share on other sites More sharing options...
Machspeed Posted March 4, 2021 Author Share Posted March 4, 2021 Jim is right - that's the bolt for right hand side lower dash support arm. G701/G106 screws to the dash support just to the right of the radio. That bolt (lower dash support arm) is what I used to beef my ground path up. Ran a heavy (2 or 4awg, can't recall at the moment) cable from the battery to that bolt. Then on the interior side I ran a cable from the same bolt to a ground bar behind the dash. From there I ran a 10awg wire to the dash support. The ground bar could be ignored and a wire ran directly from the interior side of the bolt to G701/G106. Not a modification that's really needed for most but if adding things like an amp, it's an easy way to add a reliable ground path. Well that explains a lot, I've been looking on the firewall for that ground....sheez! Thanks Scott! I'm going to test from front to back and hope I find the issue up front of the tanks somewhere. Really dreading dropping those tanks. Keep going back and forth on lifting the bed vs. dropping the tanks. Link to comment Share on other sites More sharing options...
ratdude747 Posted March 5, 2021 Share Posted March 5, 2021 Well that explains a lot, I've been looking on the firewall for that ground....sheez! Thanks Scott! I'm going to test from front to back and hope I find the issue up front of the tanks somewhere. Really dreading dropping those tanks. Keep going back and forth on lifting the bed vs. dropping the tanks. Lifting (tilting) the bed worked better for me, having done it both ways. Both are a pain in the butt, but if you're not looking to clean out/inspect the tank, tilting the bed was easier. Just beware that the rearmost bed bolts like to round out and spin... the LH rear one did that to me, and I had to wedge the head to get the nut off (and wrap/jam it with electrical tape to get it to re-install). Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 5, 2021 Share Posted March 5, 2021 Lifting (tilting) the bed worked better for me, having done it both ways. Both are a pain in the butt, but if you're not looking to clean out/inspect the tank, tilting the bed was easier. Just beware that the rearmost bed bolts like to round out and spin... the LH rear one did that to me, and I had to wedge the head to get the nut off (and wrap/jam it with electrical tape to get it to re-install). In the past I've just tack welded the bolt head to the bed. They won't turn then, and it saves turning the lozenge shaped hole in the bed round. Those bolts can get expensive. So if you can get them off without cutting them it's worth it. I think I have 7/16 stainless carriage bolts in there now. Link to comment Share on other sites More sharing options...
ratdude747 Posted March 5, 2021 Share Posted March 5, 2021 In the past I've just tack welded the bolt head to the bed. They won't turn then, and it saves turning the lozenge shaped hole in the bed round. Those bolts can get expensive. So if you can get them off without cutting them it's worth it. I think I have 7/16 stainless carriage bolts in there now. That too... If I had a welder that wasn't a junky Harbor Freight wonder, I'd have done that. The middle bolts are different (bigger keying boss) and don't seem to have this problem... only the back (and front?) ones with carriage squares were trouble for me. Link to comment Share on other sites More sharing options...
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