New World Datsuns...

I have had this tach in the cabinet for years(made for Jeep), it's brand new, I don't even know how I came to own it, so I hooked it up to the stock tach plug in the 720 harness, and it worked great, the truck was idling when I took these photos.

I hooked the light up to the tach power, so the light is on all the time now, so are the dash lights.

Here are the instructions.

why can't you take the white wire and connect it to the head light switch so your tach light comes on when you turn on the HL & dash lights ?

That way the tach light is not always on.

Ni10 » Sat Feb 21, 2015 10:01 am wrote:why can't you take the white wire and connect it to the head light switch so your tach light comes on when you turn on the HL & dash lights ?

That way the tach light is not always on.

The 720 wiring harness is a strange animal, you cannot just grab power from anywhere you want to, especially from the headlight circuit, you see if I were to try and make the little light in the tach come on with the headlights, I would be introducing a ground via the black wire in the tach, it would fuck up everything, even the headlights would come on a very little and drain the battery.
I learned all this on my first 521 kingcab conversion that I used the 720 wiring harness, so now I just grab a keyed circuit for the dash lights in everything, Charlie69 figured a way to do it in his 520 build, but he had to add a bunch of wires to his instrument cluster to make it work.
In a nut shell, the 720 instrument cluster dash lights do not have a ground, it's this closed circuit, the power goes to the lights in the cluster, and then it goes out of the cluster to the dimmer switch which has the ground, 3 wires go to that dimmer switch, figure that one out, two of them have power, in total there are 3 hot wires that control the dash lights, RY, RL, RB, and a ground wire, but no one power wire can be used buy itself with a ground, because you would be introducing a ground into the system that isn't supposed to be there, one has to use two hot wires to make the dash lights come on WITHOUT having a ground.

awe, thanks for explaining. Now I'm more confused then I was before about this Datsun wiring.

I forget that Datsun wiring is NOT the same as American car wiring. Carry on.

Ni10 » Sat Feb 21, 2015 11:16 am wrote:awe, thanks for explaining. Now I'm more confused then I was before about this Datsun wiring.

I forget that Datsun wiring is NOT the same as American car wiring. Carry on.

The 720 wiring harness is confusing to me to, I personally would like adjustable dash lights myself, but to do that I would have to have plastic bulb holders that will fit in the holes of the 521 instrument cluster lights that don't have a grounds in them, then have a small dash light harness with two wires going to each bulb to make it work, what's funny is that the oil light, charge light, e-brake light and turn signal lights only need one wire and a ground, so they wire up normal, but the brights indicator light has to have two wires like the dash lights to work properly and not mess up the headlights.

Here is a link to Charlie69s 520 build, he starts doing the dash lights on page 8 in his thread, lot of wires going everywhere figuring out how to have dash lights that work normally with a 720 harness.
https://www.google.com/url?q=http://com ... 40jN2xbFNA

I haven't had any issues with wiring in tachs to 720s myself. But, I grab power from a small light under the dash. Normally the cig lighter light. Haven't had any issues to date, or power draining. I haven't tried wiring it up to the headlights or whatever tho. Normally, tho... I just do what you did wayno. Hook up the light to the power wire for the tach, so the light comes on when the tach is on. Coolness factor for it to work when they lights do, but easier to do what you just did

Yea, Im going with, that isnt the case. Just pulled open a wiring diagram. There is no ground switching on these trucks. Standard dealio as anything else. Tapping into the Red/yellow at the light switch should work just fine, as it provides power to parking lights, and all interior lights the same.

There isnt even a headlight relay on one of these things.

Even on the screwy datsuns (like 510s and well 521s), its only the headlights themselves which are ground switched, parking lights are normal.

Laecaon » Sat Feb 21, 2015 2:19 pm wrote:Yea, Im going with, that isnt the case. Just pulled open a wiring diagram. There is no ground switching on these trucks. Standard dealio as anything else. Tapping into the Red/yellow at the light switch should work just fine, as it provides power to parking lights, and all interior lights the same.

There isnt even a headlight relay on one of these things.

Even on the screwy datsuns (like 510s and well 521s), its only the headlights themselves which are ground switched, parking lights are normal.

All 720s have a headlight relay as far as I know, here is the one on the 1982 720 harness.

I just went thru the 1982 wiring diagram on my dining room wall, I think you might be right about pulling dash light power from the red/yellow wire in the light switch, I didn't see that before, and neither did charlie69, as he went thru all the trouble of isolating all his dash lights so that they would work with the dimmer knob on his 520 instrument cluster.
I am just going to go with what I have, but I stand behind my statement I made before, one cannot grab power for a light in an aftermarket gauge from the dash light circuit in a 720, it will not work, one would be adding a ground where there isn't supposed to be one.
My next build that I use a 720 harness on, I might give that red/yellow wire a try, but it will not be an adjustable light, it will be on or off unless another dimmer is added in.

I did some work on this build today, I fixed the hole in the passenger side floor.



I made my own brake for bending metal.

I did some bending and cutting and came up with this.


Then I pop riveted it in position, then started hammering and welding.

I can run a bead becuase the metal was thick enough, and has enough bends to not warp much, but I tacked it in first.

Then I ground/wire wheeled it all smooth and primed it, I even ground the heads of the rivets off.

I am happy with this fix, it's not supposed to look stock, it's just supposed to be solid, carpet or vinyl covering will cover it up.

my 1980 diagram has no headlight relay... but then again, I have 3 wiring diagrams for my 510, and only one even showed the automatic transmission wiring correctly.

I just looked at the dimmer wiring. First thing to grasp, the lights do not need 12v and ground, they simply want a voltage differential. They would be equally as bright with one leg at 24V and the other at 12V. Now, how you dimmer works is this, the dash lights all get 12V from the headlight switch, the dimmer switch has ground and 12V as inputs, and a wire (red/bue) as a output, this output sweeps from 0v (ground), to probably 3v or 4v (merely a guess for example). This means there is a voltage differential across the bulbs from 12V to 8V, and why the lights dim.

Now to preserve wiring, and to isolate how things are done, the way I would get the tach to dim is this: Open the tach, disconnect the bulb inside from grounding with the tach, and attach a wire. Run this extra wire out of the tach as the "ground" of the bulb inside. Connect your 12V light wire for the tach to Red/yellow, and now connect your new wire from the tach to Red/Blue of the dimmer switch. Bam, 1 extra wire, and now your tach dims with the dash lights.

Laecaon » Sun Feb 22, 2015 4:21 pm wrote:my 1980 diagram has no headlight relay... but then again, I have 3 wiring diagrams for my 510, and only one even showed the automatic transmission wiring correctly.

I just looked at the dimmer wiring. First thing to grasp, the lights do not need 12v and ground, they simply want a voltage differential. They would be equally as bright with one leg at 24V and the other at 12V. Now, how you dimmer works is this, the dash lights all get 12V from the headlight switch, the dimmer switch has ground and 12V as inputs, and a wire (red/bue) as a output, this output sweeps from 0v (ground), to probably 3v or 4v (merely a guess for example). This means there is a voltage differential across the bulbs from 12V to 8V, and why the lights dim.

Now to preserve wiring, and to isolate how things are done, the way I would get the tach to dim is this: Open the tach, disconnect the bulb inside from grounding with the tach, and attach a wire. Run this extra wire out of the tach as the "ground" of the bulb inside. Connect your 12V light wire for the tach to Red/yellow, and now connect your new wire from the tach to Red/Blue of the dimmer switch. Bam, 1 extra wire, and now your tach dims with the dash lights.

Yes I understand this, but it is a major hassle trying to do that with a 521 instrument cluster, I would have to build a mini harness that is separate from the dash harness and buy 5 plastic bulb holders that would fit in each hole, now maybe if I had thought of using the red/yellow wire in the headlight switch I could have made it so the dash lights came on with the headlights/park lights, but neither me nor Charlie thought of that, and since there was clean power coming from the harness to supply power to the stock tack, I just used that power to power and illuminate the aftermarket tach also, I don't care if it is on all the time, I just put it in that truck because it been in the cabinet for years and I wanted a tach, and the only stock 720 tach I have left doesn't work, if it did, I would have made a holder for it as it is square.
This build was put together out of parts I have laying or packed away around here, the only part I have had to buy was a brake line hose for an 85 as I somehow screwed it up piping the brakes, I also bought a gallon of antifreeze, I forgot about that.

I forgot, I also installed this today, need to put in a speaker, an antenna, and then power it.


I'll work on it some more tomorrow.

Yes, I then forgot that you were using a 521 cluster... I think it may be possible... But it would take removal of the cluster, cutting a couple of traces, and adding a wire or a couple. Probably not worth it for lights that are already too dim...

Laecaon » Sun Feb 22, 2015 7:11 pm wrote:Yes, I then forgot that you were using a 521 cluster... I think it may be possible... But it would take removal of the cluster, cutting a couple of traces, and adding a wire or a couple. Probably not worth it for lights that are already too dim...

That is what Charlie69 did, he added wires to it, it looked kinda messy, but he did it in such a way as to be able to use the stock plug I believe, or maybe he only had to plug in one extra wire, I can't remember, I have two extra wires, they are for the brights indicator light that is plastic so when I put it in that hole, it doesn't ground out.

Do you need a speaker wayne??
I have a few extra, not very good but I doubt your looking for a high quality system to bump
I could bring them when I brjng you the exhaust, which I keep forgetting to do...

I believe I am good with speakers, but right now I have other issues to deal with, I would still like the exhaust system.
I might have to move, I am looking for a better place to live now.

A nice big shop with maybe a house somewhere on the property?

Well Wayne I hope it's because you want to & not from force.

DRIVEN » Tue Feb 24, 2015 7:16 am wrote:A nice big shop with maybe a house somewhere on the property?

Yea, something with a shop and parking, I found a house with a 3 car minimum garage and two carport type spaces connected to the garage with just as much room in front of them with a 1500sf home that I could put 25% down on right now, but it is 70 miles away from Vancouver where I presently live, having to drive an hour just to get to where the work is every work day is a bit more than I would like to drive, but it is in the area of me being able to put 25 to 30 percent down.
It's been 6/7 years now since I had a mortgage payment, so it might be hard to qualify for a loan also.
I would sell what I am in now and buy something, but I would need somewhere to put everything so I could get this house/property ready, I have a lot of stuff here that is not code, but most of it has been there since before the city annexed me, so legally they cannot make me remove it, but to sell it is another story, it would take some time to get it ready to sell.
I have been parking the work truck with the trailer in the same spot for nearly 20 years now, and now it's against the law, I have been in the city boundaries for 15 years now, nothing has changed except that "lowlife piece of shit" is complaining about me now instead of the guy across the street, it for some reason it became my turn, and I told him he was a "lowlife piece of shit" several times when we talked.
This isn't going to go away, he already told me he was going to complain about me again when I called him what he was to his face, as I was walking away from him he told me he was glad that he turned me in, that is when I turned around, looked him in the eyes and told him that is why he is a lowlife piece of shit, because he was glad.
What is sad is that this lowlife piece of shit has no arms, when he was a kid in Brazil I think, he got his kite tangled up in the power lines, he decided to climb the power pole to get his kite even after being told not to, he burnt both his arms off, he really wanted to know who told me that, as that was privileged information, I laughed at him and said not a chance, I should have said, "why, so you can terrorize them too", but that one got away, I didn't think to say that till later.
This guy used to have my respect, he would start the lawn mower with his foot, and push it around with his stomach, he did a lot of stuff for a man without arms, the only thing I feel about him now is contempt.

Damn, dude. I don't even know how to respond.