Gary Lewis Posted January 25, 2021 Author Share Posted January 25, 2021 Not "Yes and no" The fuse links are supposed to be two wire gauge sizes smaller than the wire they protect. You have 37 & 38. If you look at the stock diagram both are fed from the shunt. Therefore the shunt is fine (with a stock load) Using anything bigger, without hacking into the cab harness and eliminating those fuse links, is a waste that gains you nothing. I don't know what size the shunt is. Do you? As Steve83 pointed out, the shunt doesn't have to be replaced. The voltage drop across it is very small as the ammeter is very sensitive. But some people, like Ty, want to replace it, so I'm trying to figure out what size wire it should be replaced with. And the best way I could think of to do that was via the cross section of the wires it is feeding. But, I may have a shunt that I cut out of Big Blue that I can measure. I'll look tomorrow. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted January 25, 2021 Share Posted January 25, 2021 I don't know what size the shunt is. Do you? As Steve83 pointed out, the shunt doesn't have to be replaced. The voltage drop across it is very small as the ammeter is very sensitive. But some people, like Ty, want to replace it, so I'm trying to figure out what size wire it should be replaced with. And the best way I could think of to do that was via the cross section of the wires it is feeding. But, I may have a shunt that I cut out of Big Blue that I can measure. I'll look tomorrow. 37 is 10, and fuselink M is 14 AWG, which supports that. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 25, 2021 Author Share Posted January 25, 2021 37 is 10, and fuselink M is 14 AWG, which supports that. Yes, and 38 is 12 and Fuse Link L is 16 gauge. And our shunt replacement supports both 37 and 38. But I don't think we should size by the fuse links. They are purposefully undersized by two notches to be the failure point, and we don't want our shunt replacement to be a failure point. Bill's point earlier was very valid. The later trucks had the cab fed by a #4 wire running from the battery to the PDB on the driver's fender. And they don't have any electrical loads that our trucks didn't come with. Granted that wire is probably 6' long and our shunt replacement is maybe 1' long, so that changes things somewhat. Tomorrow I'll see if I can measure the size of the shunt and the big yellow wire for #37 at C610. Since we are just extending that wire then using whatever gauge it is would seem appropriate. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 25, 2021 Author Share Posted January 25, 2021 Yes, and 38 is 12 and Fuse Link L is 16 gauge. And our shunt replacement supports both 37 and 38. But I don't think we should size by the fuse links. They are purposefully undersized by two notches to be the failure point, and we don't want our shunt replacement to be a failure point. Bill's point earlier was very valid. The later trucks had the cab fed by a #4 wire running from the battery to the PDB on the driver's fender. And they don't have any electrical loads that our trucks didn't come with. Granted that wire is probably 6' long and our shunt replacement is maybe 1' long, so that changes things somewhat. Tomorrow I'll see if I can measure the size of the shunt and the big yellow wire for #37 at C610. Since we are just extending that wire then using whatever gauge it is would seem appropriate. I found the harness shown below and added some labels to the pic, so maybe we can use it in the write up. And I measured the wires, as best I could, and referred to this table to come up with the wire sizes: Big yellow wire going to the right from S202 is .115" in diameter, so should be a 10 gauge wire Orange/black wire coming from the alternator to S202 is .115" so should be a 10 gauge Shunt is .085", and while I can't find a good match in the chart, it appears to be smaller than 12 gauge but not as small as 14. Given that, I'm going to suggest that we recommend that the shunt be replaced with a #10 wire. Thoughts? Link to comment Share on other sites More sharing options...
Tyler Posted January 25, 2021 Share Posted January 25, 2021 I found the harness shown below and added some labels to the pic, so maybe we can use it in the write up. And I measured the wires, as best I could, and referred to this table to come up with the wire sizes: Big yellow wire going to the right from S202 is .115" in diameter, so should be a 10 gauge wire Orange/black wire coming from the alternator to S202 is .115" so should be a 10 gauge Shunt is .085", and while I can't find a good match in the chart, it appears to be smaller than 12 gauge but not as small as 14. Given that, I'm going to suggest that we recommend that the shunt be replaced with a #10 wire. Thoughts? I hate to distract from the conversation but as discussed, I removed my shunt wire and it was pretty burnt up upon examining it when I cut it out (fuselink J too). If I keep my ammeter disconnected, am I safe to continue operation? Link to comment Share on other sites More sharing options...
Machspeed Posted January 25, 2021 Share Posted January 25, 2021 I found the harness shown below and added some labels to the pic, so maybe we can use it in the write up. And I measured the wires, as best I could, and referred to this table to come up with the wire sizes: Big yellow wire going to the right from S202 is .115" in diameter, so should be a 10 gauge wire Orange/black wire coming from the alternator to S202 is .115" so should be a 10 gauge Shunt is .085", and while I can't find a good match in the chart, it appears to be smaller than 12 gauge but not as small as 14. Given that, I'm going to suggest that we recommend that the shunt be replaced with a #10 wire. Thoughts? I like what you're doing, Gary! Thank you! Yesterday, I was briefly looking over the stuff for my needs and wondering, where and what does this shunt look like??? I know now! Regardless, when putting stuff like this together, one has to think at the lowest level. Pictures are GREAT!!! I've got my harness (alternator side) out of the truck. Would you like a picture of it? I have the 2G alternator in my 86. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 25, 2021 Author Share Posted January 25, 2021 I like what you're doing, Gary! Thank you! Yesterday, I was briefly looking over the stuff for my needs and wondering, where and what does this shunt look like??? I know now! Regardless, when putting stuff like this together, one has to think at the lowest level. Pictures are GREAT!!! I've got my harness (alternator side) out of the truck. Would you like a picture of it? I have the 2G alternator in my 86. Ty - Which fuse link did you cut out? John - Pics, please! That would help with the write up for the 2G. Link to comment Share on other sites More sharing options...
Tyler Posted January 25, 2021 Share Posted January 25, 2021 Ty - Which fuse link did you cut out? John - Pics, please! That would help with the write up for the 2G. I only have C610. Splice 202 and 203 are cut and removed. The 2 wires for ammeter are zip tied and disconnected (orange and yellow/green trace but green in your photo above). Thick yellow is routed to battery side of mega fuse along with the 12v continuous on yellow/white trace. Green/red trace is connected to green red trace from the painless harness (12v switched). Everything else is removed. There is a photo about half way down on page 6 of the 3G Advice thread. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 25, 2021 Author Share Posted January 25, 2021 I only have C610. Splice 202 and 203 are cut and removed. The 2 wires for ammeter are zip tied and disconnected (orange and yellow/green trace but green in your photo above). Thick yellow is routed to battery side of mega fuse along with the 12v continuous on yellow/white trace. Green/red trace is connected to green red trace from the painless harness (12v switched). Everything else is removed. There is a photo about half way down on page 6 of the 3G Advice thread. You are good to go. Link to comment Share on other sites More sharing options...
Tyler Posted January 25, 2021 Share Posted January 25, 2021 You are good to go. Whew! Link to comment Share on other sites More sharing options...
Recommended Posts