Nismo280zEd Posted February 17, 2005 Share Posted February 17, 2005 I've done many searches on this so nobody gripe at me. I just want verification if i'm on the right track here. OEM 280z oil pres and fuel level gauges and sending units. If my understanding is correct, the sending unit, requires a 12-14v input, then is either grounded by what it screws into, or a seperate ground wire, then another wire sends signal to the gauge in form of varying ohms. So is this correct? -Ed (still trying to get all the electrical working right) Quote Link to comment Share on other sites More sharing options...
GrayZee Posted February 18, 2005 Share Posted February 18, 2005 Oil, temp and fuel level gauges all get their +12v power from a ignition sourced fuse. The oil and temp rise on the presence of a variable ground. The better the ground the higher the reading. For example, the sending unit is grounded, (screwed into the block) but it does not conduct to the wire until oil pressure starts to rise. If you were to turn your ignition on and take the wire off of the sending unit and ground it directly the gauge should rise to the top of the scale. Fuel level gauges are slightly different, They are just like a ohm-meter. They have the same ignition sourced +12v (as well as their own ground... ) and then there are two other wires that run to the fuel tank. These two wires are like the test leads of a ohm-meter. They measure the ohm reading (resistance) across the two terminals on the fuel tank. Every fuel tank can have a different upper and lower ohm reading. The fuel level gauge must be calibrated to match the fuel tank. For example, a typical GM fuel sender will be 90 ohms when full and 0 ohms when empty. A 280 is somewhere around 75ohms empty and 12 ohms full (not sure on the exact numbers though) If you do a search I'm sure you can find the right numbers.. Hope that helps Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted February 22, 2005 Author Share Posted February 22, 2005 That helps a little, so basically if i run the sending wire from the back of the oil gauge to the sender, then give it a 12+ source it will read. Then the fuel has two sending wires from what I understand you said, plus a 12+ and it's own ground. -Ed Quote Link to comment Share on other sites More sharing options...
GrayZee Posted February 22, 2005 Share Posted February 22, 2005 That helps a little' date=' so basically if i run the sending wire from the back of the oil gauge to the sender, then give it a 12+ source it will read. Then the fuel has two sending wires from what I understand you said, plus a 12+ and it's own ground. -Ed[/quote'] Sounds right to me. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted February 22, 2005 Author Share Posted February 22, 2005 Ok... the fuel sending unit in my 280. Has a yellow, a yellow and blue wire, and a black wire. Assuming the black is the ground, I cut the yellow figuring that was the power wire, and the yellow and blue was the sending wire, jurry riged that with no luck, so i switch wires, cut the yellow and blue put power to it... still no luck. So I have this fuel gauge made by "Tempo" for boats and i wired it in there. With it's own ground, i used the yellow wire for the sending and put power to the blue and yellow and it read half tank. So my sending unit is working yes? Am I barking up the wrong tree or still on track? -Ed Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted February 23, 2005 Share Posted February 23, 2005 Per my 78 FSM the black wire is ground ,the yellow-blue stripe wire goes to the fuel warning lamp on the floor console and the yellow wire goes to the fuel guage. LARRY Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted February 23, 2005 Author Share Posted February 23, 2005 ok.. then howz it get power? I thought the sender had to have power? -Ed Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted February 23, 2005 Share Posted February 23, 2005 The third 10A fuse down on the left side of the fuse box is ign. switch to ign. relay to 10a fuse to the fuel warning lamp and to tha volt/ fuel guage . THE yellow-blue from the fuel warning light goes to the fuel tank unit.The feed from the 10a fuse is split to the fuel guage and the yellow wire supplies pwr to the fuel unit from the volt/fuel guage. Let me add this to the above. The tank unit has a float that moves up and down with a sliding contact that slides on a resistance that controls current flowing to the fuel gauge. The gauge moves with changes in current flow. The gauge has a bimetal arm and heat coil. When ign. swich is "on" current flows to the heater coil and the bimetal arm is bent, causing the pointer to move. The yellow wire carrying the current changes from the float movement moves the fuel level pointer in the gauge. LARRY Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted February 23, 2005 Author Share Posted February 23, 2005 ok.. i know the fuel warning light works cause it came on driving once before. But... that whole area is out of the car.. so basically i broke the circuit by removing the warning lamp... so all of this testing i'm doing isn't going to work until i plug the warning light back in? < So once i plug it back in.. the yellow wire should be jumped to the gauge to test... yes? (The front half of my car burn't up about a year ago and i've been re-wiring since) However the fuel gauge hasn't worked for about 3 years. The sending unit is about a year old and i have two fuel gauges neither work when plugged in but the voltage meter works, so i'm assuming there is a split or short in the wiring somewhere. So if i ground the black wire on the gauge myself, then jump the yellow wire to the back of the gauge, it SHOULD read? yes? sorry for all the questions this one really messes with my mind Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted February 23, 2005 Share Posted February 23, 2005 Well......First if the VR is working then it's rec. pwr. thru the blue wire ( indicated L in the diag. ) from the fourth down 10a fuse on the left side of the fuse box. That fuse gets pwr from a white with black stripe from the ign. relay. The pwr for the fuel gauge is the green wire that comes from the third 10a fuse on the left. The fuel warning lamp doesn't have to be good because that green splits before the lamp so you need 2 things. A good fuse in that slot ( third down left side ) and that the green wire is good from the fuse box to the gauge. If the heater coil is no good in the gauge it won't work. If the yellow wire to the fuel unit isn't good it won't read right. LARRY Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted February 23, 2005 Author Share Posted February 23, 2005 Ok this is how I got the gauge to work finally! sender has yellow, yellow-blue, and black. followed the wires up under the passenger seat, took the seat out, carpet, back seat, etc. cut the wires under the seat. Hooked up my own ground, put power to the yellow-blue, then hooked the yellow wire up to the yellow input on the gauge, the hooked power up to the green wire on the back of the gauge, hooked up my own ground to the back of the gauge again. Fuel level slowly went up to "E" (prolly right cause the gas tank wasn't that heavy when i droped it) Btw... what page is that in your FM..? Now I gotta re-wire for the warning lamp. (thanx for all the help, I still get confused with electricity sometimes) -Ed Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted February 24, 2005 Share Posted February 24, 2005 Tracing DATSUN electrical problems is like being with my first wife...DAMN. I hope you can get everything working. That page in the section " Body Electrical System" is BE-33. lLARRY Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted February 24, 2005 Author Share Posted February 24, 2005 LoL... Hopefully my first wife doesn't give me as many troubles as this car. I recieved my racing catalogs in the mail today (Pegasus Racing) and they have Fuseblocks for dirt cheap. 20 circuit fuse block, accepts ATC fuses, rated for 30amp each circuit for 21.99 <<-At that price I might just go ahead and once i get it all working.. splice and relocate all my realays, fuses, circuit breakers etc to a board under the seat. Thanx for the advise, Ed Quote Link to comment Share on other sites More sharing options...
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