D21-SD25 Fuel Tank sender unit refitted.

SD diesels were widely available in the US in the 1981-86 Datsun/Nissan 720 pickups, and in Canada through '87 in the D21 pickup.

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Highway Man
Posts: 46
Joined: 5 years ago
Location: Hillman West Australia

D21-SD25 Fuel Tank sender unit refitted.


Post by Highway Man »

Good Morning all,

Finally I have replaced my Diesel tank Sender unit, and have wired it in as the old one came out, I bought the New replacement from a chap in Taiwan and it is a lovely job of
his Manufacturer, everything seems to fit very well, the Gauge is a "VDO" unit and is wired up nicely, but it wont work for me, do any of you chaps have a Wire diagram I could check against
my work please, an "Electrical Genius, I am not"!

As a matter of interest to you chaps, the Unit cost $65.00Au including freight, and twelve days to arrive by post.

best regards,

highway man.
Posts: 267
Joined: 14 years ago
Location: Canada

Re: D21-SD25 Fuel Tank sender unit refitted.


Post by Nissan_Ranger »

Make absolutely sure that the sending unit plate is GROUNDED to vehicle earth. If it's not, it wont work. Test the gauge circuit by removing the sender wire from the sender. The gauge should either go to 'FULL' or over 'FULL'. Then ground the sender wire to vehicle earth. The gauge should now move to the 'EMPTY" or just under 'EMPTY'. If this testing works as described, then either your sender isn't grounded or it's a mis-matched (Different resistance factor) unit, i.e., not right for your gauge impedance. 99 percent of gauges work as I described above. 1 percent will work the OPPOSITE when grounding and opening the sender wire circuit.

If the testing does NOT yield the above results, then you have either a faulty gauge, an incorrect wiring to the gauge with respect to power feed, grounding at the gauge & sender wire, NO power feed, or a wiring fault in the sender wire, i.e. either open or shorted to ground fault between the gauge and tank.

The old 'six gun' was as popular as the cell phone in its time and just as annoying when it went off in the Theater.
Highway Man
Posts: 46
Joined: 5 years ago
Location: Hillman West Australia

Re: D21-SD25 Fuel Tank sender unit refitted.


Post by Highway Man »

Well Chaps,
I have finally come to my senses and cut my loses with my Fuel Gauge problems, While I have very few troubles reading my "Fuel Dip Stick", when unloaded, I do find it a pain in the bum to
Read when I am fully loaded, and have to unload to be able to read the Contents of my tank until I remembered the Ships "Sight Glasses" and thought I might be getting cleverererer, in my
old age, and fitted this to the side of my tank so at a quick glance I can see the health of my Fuel Tank as I approach my Ute, and left the Dipstick still in place too block the Hole!

My "Amp Meter" had a Stroke and my Headlights became nightlights and I could see nothing as I groped along the Country Highway looking for a place of Safety to tie up and sleep until the
Morning Sun finally showed itself over the hills and found me in a very cold dark Valley, sitting on a cold wet Log, wrapped in my Sleeping Bag on my very cold Bum, sipping at my tasteless cup
of coffee, which when I made it i filled with Sugar instead of Powdered Milk, so It tasted like "Bilge Water" of a "floating Brothel" to me and replaced it at first light, You see, I couldn't find my lost Torch in the Dark, {no lights remember}, and my hands could not feel the difference of Sugar or Powered Milk in the pitch dark, they were that cold, and I had no Lighters as I had ceased smoking
about sixteen years ago!

I connected my little "Gen-Set" to the Battery and left it humming away to the Birds in our closest Trees and slept for two warmer hours, then after yet another coffee I restarted her after I
warmed up her "Alui Inlet" with a Hair Dryer I had bought from the "Good Guys" in Rockingham for $20.00, and we once more continued our journey home!

I have refitted the "Amp Metre" with a "Volt Metre" and added the "Sight Glass" as I said earlier and am now in the middle of giving the Old Lady a coat of new Paint to brighten Her days in
Travel, and make you all weep in Envy at Her looks as we pass you all by!

Those Bloody Batteries we carry are getting Heavier by the day, 20 Batteries weigh in at a Ton, so we don't use Overdrive at all and rarely drive over 80 K's an hour, and as I look out my
Office Window I can now see the Forgotten Sunlight after near on two weeks of Rain and Wind, and must head off outside to move towards the completion of my Paintjob while the "Gods
of the Highway" are smiling at me and my Lady!

The best too you all,
highway Man
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