Dunkin Posted March 3, 2021 Report Share Posted March 3, 2021 Howdy, I am just about finished with everything on my truck, but for the life of me I cannot figure out what is up with my fuel gauge. I sent the gauge off for a rebuild and subsequently resent it to the rebuilder to make sure it was in fact operating, which it was. I have replaced the sending unit with a new one that I know was operational, replaced all the wires and added a 12V to 6V reducer. I have tried every wire hookup combination with the last one being the one the person who rebuilt my gauges for me which is top post to ignition, center sending unit wire to #2 post and grounded the wire from the sending unit to the body of the truck. Funny that the gauge worked correctly before sending it off and it didn't even have the restrictor/reducer installed. I am stumped!!! Any suggestions? Roman 1947 WHA - 48 truck 1 Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted March 3, 2021 Report Share Posted March 3, 2021 The 1947 WH48 truck should use sender 591146 . This sender doesn't work at all like you have yours hooked up . The dash gauge has three terminals , one marked IGN for 6 volts . the other two terminals on your gauge are marked 1 and 2 . The 1 and 2 terminals go to the terminals on your sender . The float in the tank varies the resistance ( or the ground ) on a winding in the sender . 1 Quote Link to comment Share on other sites More sharing options...
Dunkin Posted March 3, 2021 Author Report Share Posted March 3, 2021 Thanks for the response Jerry. I have tried running the ground wire to the gauge and that did not work either. That is how it was set up originally or at least originally when I purchased the truck 10 years ago. As for the sending unit, I purchased it from DCM, so I will need to look and see if the number you mention crosses with the unit I bought. Quote Link to comment Share on other sites More sharing options...
1949 Wraith Posted March 3, 2021 Report Share Posted March 3, 2021 Did you take apart the original sending unit? They are quite basic, try cleaning up the windings and contact and make sure the grounding contact arm inside is clean and functioning. 1 Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted March 3, 2021 Report Share Posted March 3, 2021 If you have fresh paint or rust where your tank grounds , that would cause problems too . 1 Quote Link to comment Share on other sites More sharing options...
Dunkin Posted March 6, 2021 Author Report Share Posted March 6, 2021 On 3/3/2021 at 5:44 AM, 1949 Wraith said: Did you take apart the original sending unit? They are quite basic, try cleaning up the windings and contact and make sure the grounding contact arm inside is clean and functioning. I have not. I will take another look at the old unit, but it seemed to be one piece to where you couldn't open it up. Quote Link to comment Share on other sites More sharing options...
1949 Wraith Posted March 7, 2021 Report Share Posted March 7, 2021 On 3/6/2021 at 9:33 AM, Dunkin said: I have not. I will take another look at the old unit, but it seemed to be one piece to where you couldn't open it up. On mine the 2 sections were riveted together. I just drilled them out and riveted back together when done. Quote Link to comment Share on other sites More sharing options...
Dunkin Posted March 9, 2021 Author Report Share Posted March 9, 2021 On 3/7/2021 at 6:37 AM, 1949 Wraith said: On mine the 2 sections were riveted together. I just drilled them out and riveted back together when done. I might go this route since I can't seem to get the new one to fix the issue regardless of my wiring configuration. Thanks for the suggestion. Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted March 9, 2021 Report Share Posted March 9, 2021 I know that you have already had your gauge repaired and retested . But if you want to do a test on it yourself ; Hook up 6 volts to the IGN terminal , ground one of the other two terminals and the gauge should read full . Ground the other terminal and the gauge should read empty . 1 Quote Link to comment Share on other sites More sharing options...
Dunkin Posted March 10, 2021 Author Report Share Posted March 10, 2021 7 hours ago, Jerry Roberts said: I know that you have already had your gauge repaired and retested . But if you want to do a test on it yourself ; Hook up 6 volts to the IGN terminal , ground one of the other two terminals and the gauge should read full . Ground the other terminal and the gauge should read empty . Hi Jerry, Probably a dumb question, but other than using a 6V battery is there another method to test the gauge? I don't have a 6V battery handy. Can I use the reducer/resistor that drops current 12V to 6V and ground one of the other 2 terminals to see if that moves the needle? Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted March 10, 2021 Report Share Posted March 10, 2021 10 hours ago, Dunkin said: Hi Jerry, Probably a dumb question, but other than using a 6V battery is there another method to test the gauge? I don't have a 6V battery handy. Can I use the reducer/resistor that drops current 12V to 6V and ground one of the other 2 terminals to see if that moves the needle? A reducer that drops 12 v to 6 v is fine . 1 Quote Link to comment Share on other sites More sharing options...
Dunkin Posted March 31, 2021 Author Report Share Posted March 31, 2021 On 3/9/2021 at 2:10 PM, Jerry Roberts said: I know that you have already had your gauge repaired and retested . But if you want to do a test on it yourself ; Hook up 6 volts to the IGN terminal , ground one of the other two terminals and the gauge should read full . Ground the other terminal and the gauge should read empty . I tried this simple test and all the gauge did was twitch a bit, but regardless of terminal neither showed "full". Might need to find another fuel gauge on Ebay or something to see if by chance that is my issue. Would be nice to have an extra one anyhow. Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted March 31, 2021 Report Share Posted March 31, 2021 The points on these gauges are very fragile but they can be carefully cleaned . I have had NOS fuel gauges that didn't work until I cleaned the points . Also the gauges are adjustable as described in the shop manual . But if your gauge only " twitches " , the adjustment isn't likely to help . Some of them just don't work even after cleaning the points . 1 Quote Link to comment Share on other sites More sharing options...
maok Posted March 31, 2021 Report Share Posted March 31, 2021 On 3/10/2021 at 3:35 PM, Dunkin said: Hi Jerry, Probably a dumb question, but other than using a 6V battery is there another method to test the gauge? I don't have a 6V battery handy. Can I use the reducer/resistor that drops current 12V to 6V and ground one of the other 2 terminals to see if that moves the needle? Don't use a resistor, it wont work, use the an electronic reducer that you can purchase (ebay, etc) for less than 20bucks. Also, to test the gauge itself, you can test it with a potentiometer (variable resistor), 0-200ohm would be ideal. If the gauge works smoothly and well with the potentiometer then look at your sender. 1 Quote Link to comment Share on other sites More sharing options...
Dunkin Posted March 31, 2021 Author Report Share Posted March 31, 2021 35 minutes ago, maok said: Don't use a resistor, it wont work, use the an electronic reducer that you can purchase (ebay, etc) for less than 20bucks. Also, to test the gauge itself, you can test it with a potentiometer (variable resistor), 0-200ohm would be ideal. If the gauge works smoothly and well with the potentiometer then look at your sender. Sorry, I probably used the wrong term. What I used was what DCM recommended which is a LE-102 12 volt to 6 volt Voltage Reducer. Quote Link to comment Share on other sites More sharing options...
Dunkin Posted April 6, 2021 Author Report Share Posted April 6, 2021 I took my gauge out to make it easier to work on. I am cleaning contacts and cleaning the contact areas where the screws bolt up to the panel since I was told it needed to have a good clean ground. Ignition goes to the voltage reducer which goes to my 12 ignition wire. The voltage reducer is also grounded. The #2 post goes to the sending unit and the 2nd wire from the sending unit is grounded. Weird thing is that this gauge worked before without the reducer and had both sending unit wires attached to it....I've tried going that route again, but nothing. Quote Link to comment Share on other sites More sharing options...
maok Posted April 6, 2021 Report Share Posted April 6, 2021 Now you can bench test it with a 12volt battery, your 12v-->6v reducer and a potentiometer. 1 Quote Link to comment Share on other sites More sharing options...
chrysler1941 Posted April 6, 2021 Report Share Posted April 6, 2021 You gauge is unlike the modern gauges used today. All the advices given here to test it is for the later type. Your gauge has two thermostatic bimetal blades and measure the balance between the two resistors from the sender. This principal gives a more precise and calmer reading. There is a lengthy 2 page description and calibration procedure in shop manual. Seems people are back at the crude 6v reducers again ? 1 Quote Link to comment Share on other sites More sharing options...
Dunkin Posted April 6, 2021 Author Report Share Posted April 6, 2021 12 hours ago, chrysler1941 said: You gauge is unlike the modern gauges used today. All the advices given here to test it is for the later type. Your gauge has two thermostatic bimetal blades and measure the balance between the two resistors from the sender. This principal gives a more precise and calmer reading. There is a lengthy 2 page description and calibration procedure in shop manual. Seems people are back at the crude 6v reducers again ? Are implying that the reducer is not needed? My fuel gauge worked perfectly without the reducer prior to rebuilding the gauge and rewiring my truck. Quote Link to comment Share on other sites More sharing options...
chrysler1941 Posted April 6, 2021 Report Share Posted April 6, 2021 14 minutes ago, Dunkin said: Are implying that the reducer is not needed? My fuel gauge worked perfectly without the reducer prior to rebuilding the gauge and rewiring my truck. It will work with 12v but you might burn the bi metals and give wrong indication. You need 6 v for correct gauge reference. I was commenting reducing 12v to 6v using a resistor is a crude method. A better way is using an electronic converter available on ebay. There was a lengthy thread about this some time ago. Also your gauge needs the original two post fuel sender. As mentioned earlier, if you want to know more how fuel gauge work and calibrate, I'll paste pages from the manual. Quote Link to comment Share on other sites More sharing options...
Dunkin Posted April 6, 2021 Author Report Share Posted April 6, 2021 27 minutes ago, chrysler1941 said: It will work with 12v but you might burn the bi metals and give wrong indication. You need 6 v for correct gauge reference. I was commenting reducing 12v to 6v using a resistor is a crude method. A better way is using an electronic converter available on ebay. There was a lengthy thread about this some time ago. Also your gauge needs the original two post fuel sender. As mentioned earlier, if you want to know more how fuel gauge work and calibrate, I'll paste pages from the manual. This is the original fuel sender that was in the truck when I bought it 10 years ago. I can purchase a 2 post sender on Ebay if need be, but I've been advised that I can simply just use the "ignition" and "#2" post leaving post #1 empty. I will do some research on the electronic converter you speak of. Quote Link to comment Share on other sites More sharing options...
Dunkin Posted April 10, 2021 Author Report Share Posted April 10, 2021 On 3/9/2021 at 2:10 PM, Jerry Roberts said: I know that you have already had your gauge repaired and retested . But if you want to do a test on it yourself ; Hook up 6 volts to the IGN terminal , ground one of the other two terminals and the gauge should read full . Ground the other terminal and the gauge should read empty . Hello Jerry, Since I removed my gauge I decided to retest it. The needle without power sits around 3/4's full on the gauge. I hooked up 6V to the IGN terminal and grounded terminal #1 which moved the needle slowly to the completely full reading. I then grounded terminal #2 and this time the needle also moved to the full reading by it moved very rapidly. Any ideas? Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted April 11, 2021 Report Share Posted April 11, 2021 2 hours ago, Dunkin said: Hello Jerry, Since I removed my gauge I decided to retest it. The needle without power sits around 3/4's full on the gauge. I hooked up 6V to the IGN terminal and grounded terminal #1 which moved the needle slowly to the completely full reading. I then grounded terminal #2 and this time the needle also moved to the full reading by it moved very rapidly. Any ideas? The gauge will normally move to the empty position without any current at all . If it were me , I would be looking for another gauge . Quote Link to comment Share on other sites More sharing options...
chrysler1941 Posted April 11, 2021 Report Share Posted April 11, 2021 I don't want to step on anyone toes, so my answer are for others who may stumble on this thread in future with fuel gauge problems. As mentioned earlier this fuel gauge unlike newer electromagnetic types. Newer work on coils on the principal of one sender resistor connected to ground activating a couple of coils. This older thermostatic type works on balance principal and has no coils in gauge, but 2 heated bimetal blades. Sender has 2 output and resistor is not grounded as in newer models. So there is always a certain current value flowing from both sender terminals to gauge and whatever current his highest, needle will move correspondingly. This principal is high end, more precise and makes gauge less bouncy. Shorting one terminal to ground will heat up the bimetal and needle will move faster and may do harm. Included here is 3 page copy of gauge and sender testing from Chrysler manual. And another 3 page from the 1950 Service reference book. Pages from Chrysler Shop Manual C28 C30 C33.pdf Pages from 1950 Gauges.pdf 4 1 Quote Link to comment Share on other sites More sharing options...
Dunkin Posted April 11, 2021 Author Report Share Posted April 11, 2021 7 hours ago, chrysler1941 said: I don't want to step on anyone toes, so my answer are for others who may stumble on this thread in future with fuel gauge problems. As mentioned earlier this fuel gauge unlike newer electromagnetic types. Newer work on coils on the principal of one sender resistor connected to ground activating a couple of coils. This older thermostatic type works on balance principal and has no coils in gauge, but 2 heated bimetal blades. Sender has 2 output and resistor is not grounded as in newer models. So there is always a certain current value flowing from both sender terminals to gauge and whatever current his highest, needle will move correspondingly. This principal is high end, more precise and makes gauge less bouncy. Shorting one terminal to ground will heat up the bimetal and needle will move faster and may do harm. Included here is 3 page copy of gauge and sender testing from Chrysler manual. And another 3 page from the 1950 Service reference book. Pages from Chrysler Shop Manual C28 C30 C33.pdf 1.6 MB · 4 downloads Pages from 1950 Gauges.pdf 1.17 MB · 2 downloads Thanks for sending this, it's very informative. Me and my friends were not 100% sure how these worked, so this helps. We are impressed with whomever came up with this over 70 years ago. I am not well versed with electrical components, so forgive me if this is a dumb question...in looking at the shop manual regarding this gauge, is testing/calibrating based on the truck being positive ground? Quote Link to comment Share on other sites More sharing options...
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