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Auzzie 521 build thread.


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Been waiting a long time to start a build thread. And here it is!


I have a 1971 521. Body in good enough condition.


Will be putting the 521 on a 720 chassis. Obvious reasons why. Better motor,breaks,suspension,can have a auto transmission, gear ratios good for highway use, blah blah blah....


How I got the 521



I straightened the front out best I could. I'm definitely not a panel beater! A quick wash/scrub and put the 720 mirrors on her.



Picked up a 1982 720. Mechanically in top condition.



Currently where I am up to on the stripping of the 720.




Will be using a L4N71B transmission.

521 has a alloy H190 diff, don't know it's gear ratio. I spend most my time driving at 100km/h, so depending on revs I will decide which diff to go with.


Found a wiring diagram for both utes.

Anyone got any hints or tips to make the swap as painless and easy as possible? Figured I'll swap as much as possible over to the 521 then lift/roll the 720 body off it's chassis. I'm in a wheelchair and want to do everything by myself except for transferring the 521 body over.

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So your going to have a really long tray/flatbed?

I have done this several times, I have put 2 Datsun 521 cabs on 720 frames and 1 Datsun 520 on a short 720 frame, all but one were put on long frames like yours, I also use the 720 wiring harness in my 521s along with the 720 steering column.

Here is my 521 kingcab thread.


Here are my 520 threads



Here is another one I did.


Never seen anyone strip down a 720 double cab on here before, we all would like to have one of them.

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Wayno, I'll be using the 521 tray. That's a standard size here in Australia. Lined up the 2 dattos wheel to wheel and they are the same length.


Lockleaf, I'll swap you a complete dual cab for a 521 tub hahahahahahaha!


Charlie69, we got heaps of them here. I only felt a bit bad when stripping it did I realise its an original ute. Never been in a accident. The body is just rusted out. Also cheers for the advice on what diff to run.


Does the 720 wiring harness plug into the 521 dash components? My plan to cut the harness at the firewall and joining then with fuses.

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DEAL. You pay all the shipping :).


Before you cut any wires, spend a good while talking to Charlie and Wayno about how they retro fitted 720 harnesses to those trucks.


I also have a '71 510 with a 720 harness in it, but I'm using all the 510 switches and gauges etc. My thread is called "half pint - z22 swapped goon". There is a link in my signature if you're interested.

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Ummm....I'll get back to you on that one.


Cool cool will do. I have wiring diagrams for both Utes. I planned to use them to make sure I got all the wires connected right! But I will definitely ask Wayno and Charlie for advice.


Sweet, I'll check your thread as well. More knowledge the better.

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Wayno, I'll be using the 521 tray. That's a standard size here in Australia. Lined up the 2 dattos wheel to wheel and they are the same length.


Lockleaf, I'll swap you a complete dual cab for a 521 tub hahahahahahaha!


Charlie69, we got heaps of them here. I only felt a bit bad when stripping it did I realise its an original ute. Never been in a accident. The body is just rusted out. Also cheers for the advice on what diff to run.


Does the 720 wiring harness plug into the 521 dash components? My plan to cut the harness at the firewall and joining then with fuses.


So you have a 521 chassis that has the same wheel base/is the same length wheel to wheel as the 720 kingcab/dual cab chassis, we didn't get longbed 521 trucks over here in the USA, all we got were short beds, so even if you could find a good tub over here, it would not be long enough.


The instrument cluster is the hardest part, the turn signals and ign/oil lights are straight forward, so are the gauges, wire to wire for the most part, but the dash lights and high beam indicator light are not, the high beam indicator light needs a 2 wire plastic bulb holder that will fit into the high beam socket hole and you need to use the 2 wires in the 720 wiring diagram for it to work, as the 521 instrument cluster uses a ground in the cluster to make this light work, the 720 cluster don't use a ground for the high beam or dash lights, to power the dash lights I would use the side marker light power(red/yellow line) in the light switch harness(column harness)to power the dash lights, but they are on full power(no dimmer), also the square headlights in the 720 are wired differently than the round headlights in a 521, so you will need to make 3 pigtail wires for each outside headlight and wire it correctly for the headlights to work, I am sure that somewhere in one of my threads(69 Datsun 521 kingcab??) I describe what wire goes where, I also describe what wire goes where to wire the 521 wiper motor into the 720 harness, I use the 521 wiring harness plastic plug by plugging the 720 wires into the proper places, it looks OEM that way.

I am fairly sure I describe most of the wiring in the 69 Datsun 521 kingcab thread except for the updates I described above about the dash lights, Charlie69s 520 thread also has the info about the wiper motor with photos and wire color to wire color, using the 720 column, by the way, the 720 non-tilt column bolts right into the 521 without any mods except for that plate at the firewall, it needs to be cut off or shaped and adjusted to the proper height then screwed to the floor/firewall, and then you just plug all the wiring into the 720 column electrics and you are good to go, you have everything, lights, turn signals, 4 ways, brights, wipers(intermitant, slow, fast), you don't have to wire any of that, it's plug and play.

I went thru most of this in the 69 and 1970 521 threads and the 520 thread I posted links too in my first post to this thread above, the 1970 521 thread I used a non-tilt column.

Here is what I wrote in the 1970 521 thread about the headlight wiring.

OK, this is what I did today, I mounted the headlight buckets, then I started on the headlight wiring, since the 720 had square headlights, and they are wired differently that the round headlights, I had to start by rewiring the headlight plugs, there are 3 wires to the outside headlights, they are all red, but I will refer to them as solid red(no line), yellow line, and black line, the solid red wire stays the way it is, but the yellow and black line get reversed, in other words, yellow line goes where the black line is, and black line goes where the yellow line is, it's that simple unless one doesn't know that, then one has to test the wires till you find the right combination, I had forgotten, so I had to figure it out again. icon_lol.gif

Here is what I wrote about the dash wiring in that thread


I cannot find the wiring description for the wiper motor, it's likely described in my 69 521 thread, and I know it is in Charlie69s 520 thread.

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I found this in my 520 build notes I will keep looking I know you sent me the wiper info with pictures.


Wayno’s 520/521 Gauge Cluster to 720 Wiring Harness



Coil Br & WL, Tac YR fuse panel to dash voltage regulator, BL tac resistor then changes to WL to coil, B                                                                                                                                   


Wayno’s 720 to 520 Gauge Cluster Tips

Hi beam is red with black line that goes to the white plug, and red with green line that goes to the blue plug. These two wires are the ones that need a isolated light from radio shack light that will fit into the high beam indicator hole without grounding. All these wires above this statement and below are the ones that go from the plugs to the instruments, not the plug to the rest of the wiring harness.

The illumination wires are red with yellow line going to the white plug as well as the controller and cigarette lighter, and the red with blue line that goes to the blue plug as well as the controller. I was never able to get the dash lights to work properly as the dash lights go to ground in the 521 dash, but do not go to ground in the 720 dash. I was able to get the charging light to work properly in the 521 dash with the 720 harness, same with the oil light and water temp gauge, and fuel gauge. Keep in mind that I am using a 720 charge system, no external voltage regulator I use a 720 alternator, internally regulated. Wayno


The thing about the 520-21 instrument cluster is all the lights in it are grounded to complete the circuit, the 720 cluster is not like that, the dash lights do not go to a ground to work, if you look at the back of a  720 inst. cluster wiring board, you will see that there is no common ground anywhere, everything goes into the cluster circuit board from the wiring harness and then goes back out into the wiring harness, each circuit is it's own little stand alone harness, and if you put a wire in there were it doesn't belong, it screws everything up. The dash lights were a problem for me, I spent a lot of time trying to get the adjustable dash lighting, i finally gave up and just pulled power off of something else light related, the problem is the lights on the 520-21 cluster use the ground to complete the circuit, the 720 uses the dash light dimming control for the ground. If you look close at the wiring diagram for the 720 dash cluster, there is only one ground in the whole cluster, and it is for the, glow plug light, right turn light indicator, left turn light indicator, and the temp and fuel gauges. All these things easily wire into the 520-21 dash and work properly, because they all ground out the same way in the 720 dash. The high beam indicator is not wired that way, it is wired into the headlight circuit, no ground. Do you have access to a 521 wiper motor? If not, you may still be able to use the 520 wiper motor, you would only have regular speed and intermittent, no fast speed. Be aware that I smoked/ruined two wiper delay boxes/units figuring out the correct place to put each of the wires.  Wayno

Wayno’s 720 intermittent wiper wiring to 521 2 speed wiper motor

Here we go, the 521 wiper motor wire colors are, black, yellow, blue, blue with red line, and blue with white line.

The 720 wire harness wire colors are, black, blue with white line, blue with yellow line, blue, and blue with red line, and that is how it goes together in the plug.

 521 black to 720 black,
 521 yellow to 720 blue-white,
 521 blue to 720 blue-yellow,
 521 blue-red to 720 blue,
 521 blue-white to 720 blue-red


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Cheers Wayno and Charlie for all your electrical knowledge!

Didn't mean to waste your time but I will be sticking with the original 521 wiring.


Haven't done much to the 521, been helping my mate prep his V8 120y for summernats. Now that it's over I can get back stuck into my build.


With the wiring, I have come to the conclusion that a retard hanging up side down looking through a shattered mirror had an attempt at rewiring it.

1st piece of evidence was a lot bolted to the negative terminal. Took most of them off and tested them on the positive and I magically have dash lights, indicators, wipers,high beam.


That's it so far but the day is still young!

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Yeah that's what I have done and everything seems to be working kinda fine...


I think the high/low beam has been switched around.

I can't find the light relay. Not under the dash. Not behind the battery with the horn relay. Though I can hear it click when changing beams.


Also after a minute or so of the high beams and a indicator being turned on they won't work. All other interior lights and low beam still work. Turn the ignition off and back on and high beam and indicators work again.


Will give the fuse box another clean just in case and will make a new 6 pin plug under the dash. It seems to get a bit hot.

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You might be able to keep both tanks if you use that 521 flatbed/tray, but I believe you are going to need a new tray or you will need to add to the back end of that one, as it is likely not long enough, all the mounts are going to have to be redone, I also would add to the side to hide the tank.

I do not believe that is a 521 tank, as the 521 tank has the fill tube in the middle of the tank on the side/top, not on the side on the end.

This is my 521 work truck, it's a dually.


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DAMN! You're working that truck!


All the mounts on the tray will line up with the 720 frame. For what ever reason the PO of the 521 "lifted" the tray. By not transferring the "lifted mounts" the trays original mounts will sit level and perfect on the 720 frame. The tray is the right length, measured it all. i too had worries about that at first look.


My best mate and I both agree that the 521 was once a late 70's mid 80's mini truck. Interior is mostly painted black and had newish tape player, exterior a different blue, side exist exhaust, lifted tray to drop the ass more, and wider rear tires on the stock rims for that fat look. So i'm not surprised that it isn't the original fuel tank.


Will definitely be doing something to hide the tank. That didn't even cross my mind!!! 

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I'm in the same boat. i want the tray to be as low as possible so its easy for my to load my wheelchair onto it while sitting in the driver seat. I have tested it a few times when I first got the 521 but a inch lower is always easier. I just cant make it to low as i want the front to look like the fender is sitting on the tire when looking at it from a side view and it to be level, so just a bit lower than your work truck.

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Mine has slightly over 100mm clearance between the tires and the wood bed bottom, but I load my flatbed/tray up a lot with debris from my work, so I have a half ton or more on the bed all the time, but I have 2 extra leafs in my rear leaf pack on each side, I also have over load air bags for when I load the truck up with wood.

If your not going to load the truck up with heavy loads, you likely could get away with 70mm, maybe a little less, and if you put a plate where the wheels are and cut the wood bed out of that area you could go around 40mm lower, or even put a fender well there, you could get the bed floor really low.

You can lower the front by loosening or re-indexing the front torsion bars, but there is a point where the good ride goes away, you could also buy drop spindles, that will get you a 2 inch drop right away.

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Just did some quick rough measurements. The gap between tire and tray is 175mm.

The tray is lifted 45mm.

I would like to drop the front 100mm (and rear to match)


I will eventually be going the 4x4 leafs. That will give me the little bit lower I want to level the truck and also stiffer seeming there won't be much gap between tire and tray.


I'll only be playing with the torsion bars. No re indexing or drip spindles.

And I will never cut the tray! Original wood still in great condition.


I won't be using the dato as a work truck. That's what the 4x4 Mitsubishi Triton is for.

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