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Jake's 320 Build


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On 1/2/2019 at 9:46 PM, emceefarlane said:


thanks! that means a lot considering there are so many great looking ones around that i aspire to!



I have a 320 as well.. But I just don't have the heart to repaint or modify it, as I purchased it from an elderly lady who's husband died. I have all the documents from day 1 at the dealership and maintenance records all the way up until the 80s when it died. Matchning numbers, too, with verifiable documents.


You can check it out here! : 


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Can anyone think of a reason why i can't this tachometer to work?


I've wired it as per the diagram and while trying to fault find i hooked it straight to the car battery for power so there's no possible interference from any other wiring

it illuminates and starts fine while the car is off but as soon as the car is running it wants to constantly restart itself (it flashes and you can feel the motor in it clicking). this happens regardless of whether the signal wire is connected to the coil or not.

i thought it might be a problem with the voltage it's getting from the battery while it's running so i tested it on my hilux while it's running and it's fine.

i bought one of these last night in the hope that the capacitors would smooth out the voltage signal https://s.click.aliexpress.com/e/eccsL2t

but i got impatient and bought 2 6v batteries to run in series to power the tacho

after testing today with the 6v batteries the tachometer starts fine and only flashes and wants to restart when the signal wire is connected to the negative terminal if the coil

i did some googling and i looks like the negative side of the coil normally goes to the distributor? that's not the case in my 320 as the positive side of the coil goes straight to the dizzy

i hooked the signal wire to the positive side of the coil and the same thing happens

i believe the car has been converted to negative ground previously because the negative cable from the battery bolts straight to the motor and the cd player etc i have installed all work fine

sorry if this is a mess but it's hard to explain

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pretty sure it's a generator? looks original & doesn't look like any alternator i've seen before and it still has the external voltage regulator.

i have a parts truck here that has an alternator from a suzuki and it has had the regulator removed so i guess mine is still a generator yes

not 100 percent sure what the difference is tho

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Sometimes these modern tachs need a pull up resistor to get enough voltage to power the tach. Basically, it's a resistor (usually 1/4 watt, 1000 ohm) connected between 12v keyed positive power and the power wire on the tach.


Here are some links to help you find what you need:


The Speedhut instructions have a good diagram about halfway down the page - https://www.speedhut.com/instructions/2_and_2_58_tach.pdf






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So the engine runs the way it is wired(negative ground), does it charge the battery this way?

Positive ground trucks are wired weird compared to negative ground trucks, I believe the positive side of the coil goes to the distributor on a positive ground truck, but I cannot remember how the negative side of the coil is wired anymore, it has been a while since I thought about this, and the link I had about this stuff is no longer good.

Try something, does the CD player have a radio antenna, if it does disconnect the antenna and try again.


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I'll try both the radio and the resistor trick


Tacho powered from 6v batteries in series



Coil is wired up with positive from the ignition going to the negative side of the coil

The positive side of the coil goes to the points of the distributor


I tried testing if this was wired correctly last night by switching polarity and checking if i was getting a positive reading on my multi-meter - however i got a negative reading both ways. I endedd up with a boot when it arced out to my hand,through me and then out my other hand on the key. i closed the roller door after that


Truck generator and regulator




Parts truck alternator & no regulator





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To me that appears to be a positive ground truck, my guess would be that it is not charging the battery.

I have no idea what has been done to that truck, but I can say this for sure, do not change the battery cables around to positive ground until you remove the radio from the system as you could smoke it thru the antenna for sure, and they are not made to work on positive ground systems, it could destroy it.

Also like i said I do not know what was done, the generator could have been modified to be used as negative ground, but it looks old and most shops that would do that kind of thing would clean it up, also I doubt the original voltage regulator would work on a negative ground system, so I am guessing it is not charging the battery, but again I do not know what has been done to the truck.

I bought a U320 that came from Australia, it was wired negative ground and had an alternator from a British car, I cannot remember if it has a internal or external regulator right now, but it wired for negative ground.

My guess would be that your radio/CD player will not work on a positive ground system, so you should take it out before testing things, I also doubt that the tachometer will  work on that truck the way it is either.

I have a positive ground truck that looks just like yours, I have all them things you took photos of, my white wire with a red line appears to be on the same post as yours, the other post yours has a white wire with a black line, mine appears to be a solid white wire, and both the ground wires are screwed to the body of the generator, again I do not believe your system is charging, check the voltage of your battery when not running, then start it and check the voltage, my guess is that it will be the same, if it shows a couple volts more then it is charging and I have no idea what was done to the truck, it looks like it is wired as a positive ground truck to me.

Again, your radio/CD player can/could be destroyed if your not careful, at the very least I would unplug the thing from the wiring in the truck and pull the antenna wire from the unit, the reason I keep talking about this is because the antenna ground is a dedicated ground that is not reversible, like the matchbox distributor the housing of the unit is and always will be a ground no matter what you do unless you know how to go inside both them units and completely rewire them which I seriously doubt can be done to the matchbox distributor or a modern radio, if you reverse the battery cables the antenna will be a direct short, it could possibly even cause a fire.


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Wayno, I've had this car for around 10 years and this is only it's second battery. It definitely charges with the current generator and wiring setup somehow. The old AM radio that came with the truck worked fine until i unplugged the speaker from it. The new CD player i installed in the glove box and wired negative ground has been working for the last 3 ish years with the antenna plugged in with no issues. The amp i installed for the speakers is also wired negative ground. The electric fuel pump i installed is also wired negative ground.

The negative terminal of the battery 100% is connected with a metal braid to the engine

So i've got a negative ground truck still running a positive ground set up somehow?


I tried unplugging the antenna last night to check if the tacho would work but it made no difference

I also ran the engine up to temp and then swapped the wires on the coil over from the current set up which is + to the distributor and power from the ignition to - terminal 

After i'd swapped them the seemed to idle okay but would backfire through the exhaust when the engine was revved

Also tested the tacho with this configuration but it still flashed and wanted to restart


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Basically I wanted to make sure you disconnected the radio if you decided to try it positive ground, as the antenna would have been a direct short with no fuse, that could start a fire.

So maybe 10 years or more ago the generator was redone to work as negative ground, they can do that to alternators also(wire them for positive ground) but it can get expensive.

Maybe the tach doesn't like the truck, do have another older vehicle you can try the tach on to see if it works?

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So my first question would be is the positive ground coil from the factory different than the common negative ground coil that is in use today?

My 1963 Datsun L320 is positive ground, it had the positive side of the coil going to the distributor, but it didn't start worth a shit, I got sick and tired of wearing down the battery trying to start the thing with it barely even trying to hit let alone start, so I figured out that the MG Midget electronic ignition distributor fit on the Datsun E1 engine, then a few days later I figured out that the MG Midget electronic ignition distributor with a Crane ignition system in it could be wired positive ground, I installed it that way and it has been in there since, it has never started/run better than it does now.

I wrote an article about this here in the 320 section.

What is really weird is that to wire an MG electronic positive ground tach into this system, I have to wire the power wire from the ignition thru the tach then to the crane ignition system to power it and the tach is supposed to work that way, I would post a link to the Crane wiring diagram but that link is no good anymore.

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  • 2 weeks later...

Okay so i started the negative ground conversion process from the start


-leads were already wired pos to the starter and neg to the motor so i didn't need to do anything there

-polarised the generator by arching it out

-swapped the ignition/switch wire from the negative terminal of the coil to the positive 

-swapped the wire to the distributor from the positive terminal of the coil to the negative side of the coil


Car runs fine

Still can't get the tachometer to work

As soon as the signal wire is connected it continually flashes and restarts


veginning to wonder is it's the tacho itself now







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I wonder if you need a tach adapter - https://www.holley.com/products/accessories/tach_adapters/


Call the tach manufacturer and talk to someone in their tech department. I called Speedhut when I first started using their tachs, and their tech guy walked me through the process. His info was ultimately wrong...but it did help.



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It sounds like your truck is now negative ground, so the - on the coil should go to the distributor. Just swap the + and - lugs attached to the coil to make it this way.

When you had your tach connected to the - side with the coil still set up for + ground, it was going to the ignition 12V.

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The way i solved this issue was to bin the tacho i had and buy another one 


This is the one i couldn't get to work https://www.aliexpress.com/item/2-52mm-7-Color-LED-Car-Auto-Tachometer-Gauge-Meter-Pointer-Universal-Meter-AD-GA52RPM/32835941372.html?spm=a2g0s.9042311.0.0.fe104c4dY5daaB

i think ultimately it was too sensitive and would likely work fine on a newer car with a clean ECU output


I bought this one which is physically much deeper and heavier https://www.aliexpress.com/item/2-52mm-Universal-Smoke-Lens-Auto-Tachometer-White-LED-0-8000-RPM-Gauge-Car-Meter/32870448864.html?spm=a2g0s.9042311.0.0.fe104c4dY5daaB

I think it has an inbuilt induction loop and basically worked straight away 

I had to buy a deeper mounting cup for this one which i haven't put on yet https://www.dx.com/p/52mm-single-dash-gauge-pod-mount-holder-for-car-motor-black-2015471#.XH8yP4gzaUk


I also had an issue with my electric fuel pump 

I've cooked two of this type https://www.supercheapauto.com.au/p/goss-goss-low-pressure-fuel-pump---universal-ge239/340609.html


and decided to upgrade to this type which so far has worked quite well


I also re-routed the fuel line so that the inline filter is mounted vertically and acts as a reservoir 


Here's a vid testing out the tacho




And i also got married! and used it as the wedding car







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