Trenchking Posted October 24, 2017 Share Posted October 24, 2017 98 ch 613 Changed fuel tank sending unit, still don't read right! Never reads above 5/8 of a tank, sometime between 0 & 5/8 just randomly moves between empty & 5/8, no set pattern. Could it be the gauge itself, maybe? Or what? Thanks HP Quote Link to comment Share on other sites More sharing options...
0 eddeere Posted October 24, 2017 Share Posted October 24, 2017 Do you have a good ground ? Quote Link to comment Share on other sites More sharing options...
0 Mack Technician Posted October 24, 2017 Share Posted October 24, 2017 Run a spare ground wire and check signal voltage. Check chassis record and make sure you have the right one that is not hitting the wall and be certain you have not clocked it degrees off during installation. Quote Link to comment Share on other sites More sharing options...
0 Trenchking Posted October 25, 2017 Author Share Posted October 25, 2017 What should signal voltage be? Pretty sure it's not hitting sides of the tank! I'll run a ground, directly to the battery,& see what that does Thanks Quote Link to comment Share on other sites More sharing options...
0 Mack Technician Posted October 25, 2017 Share Posted October 25, 2017 I have the Mac III diagram... Three terminals on your dash fuel gauge, I & S & G. The gauge "I" terminal receives 12 volts from fuse 19 and sends power out of the "S" terminal to sender unit in tank. Power goes to tank, through the variable resistor in tank sender and to ground wire/chassis. Quote Link to comment Share on other sites More sharing options...
0 lanejohn996 Posted February 12, 2022 Share Posted February 12, 2022 I'm working on a 1989 R model mack and the wire for the fuel sending unit has been cut for a long time and I can't seem to find it could you help me find it coming out of the fire wall Quote Link to comment Share on other sites More sharing options...
0 Joey Mack Posted February 12, 2022 Share Posted February 12, 2022 How about taking the dash panel off and following it from the gauge to where it goes through the firewall, my best guess is it goes to one of the buss bars on the top left corner of the firewall.. there should be 2 wires at the sending unit, one is a ground... jojo 1 Quote Link to comment Share on other sites More sharing options...
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Trenchking
98 ch 613
Changed fuel tank sending unit, still don't read right! Never reads above 5/8 of a tank, sometime between 0 & 5/8 just randomly moves between empty & 5/8, no set pattern.
Could it be the gauge itself, maybe?
Or what?
Thanks
HP
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