Factory Tach Wiring

[LenRobertson]

I got a 510 factory tach last weekend. I read some of the back posts here on tach wiring and think I have it figured out. I have two white wires with bullet connectors coming out of the lower rear face of the tach. Neg wire from the coil should connect to one and neg from the matchbox connect to the other one. Polarity matters so it may be necessary to switch the wires. Let me know if that doesn't sound correct.

 

Is 14 gauge wire heavy enough to go from the coil to the tach and back to the dizzy? I always think of 14 as being reasonably heavy but it needs to carry all the current from the coil to the matchbox through an extra 7 or 8 feet of wire..

 

Does the three wire plug wired to the back of the tach need to be hooked up for the tach to work? I can see part of what it does is hook up the two warning lights built into the tach but does it also power something in the tach that moves the magic needle? I'd like to test the tach before installing it and don't know if this plug needs to be powered.

 

Len

 

 

[dgi]

Yes, power is necessary.  

 

Here is my short write up on factory 510 tach wiring that should help you.  It also discusses wiring to a matchbox.

 

dgi

[MikeRL411]

14 gage is kind of light, 12 gage is what most houses are wired for, my house has 10 gage wiring!  Overkill? probably, but my lights don't flicker when the modern TV and Computer room gadgets kick in.  Message?  Go heavy on the wiring and you will be glad that you did.

[LenRobertson]

dgi - Great tach write-up which I hadn't seen before. I think all the info I need is there although I must wait till tomorrow when I'm more awake to reread it. Lots to absorb there.

 

MikeRL411 - Yeah, I was afraid 12 gauge might be better. The bullet connectors I have are for 16-14 gauge but I may be able to use them on 12 ga, or wait until Monday and trade them for proper 12 ga. connectors. They love me at the local auto parts place. I almost always exchange what I buy for a different part since I seldom know quite what I'm doing. Trial and error is how I go through life.

 

Len

[LenRobertson]

So I worked on the tach install today. It is in place in the dash although if it has to come out again for some reason I won't be surprised. I'm stopped at the moment since I can't find the three pin connector from the main harness that the connector from the tach plugs into. I suspect it is under the dash tucked away somewhere. I was pleased I didn't need to remove the entire instrument panel to install the tach, but now I'm wondering if I may not need to remove it just to find the elusive plug. I'm going to try looking for the plug after sundown with a powerful flashlight.

 

In my original post I said "...the two warning lights built into the tach..". Now I understand the obvious - those are the illumination lights for the tach face when driving at night. The original Oil, Charge, and Parking Brake lights stay in place and the tach fits over them.

 

Len

[dgi]

The connector is usually folded back on the harness and held with a loop of tape.  In late cars that tape loop is usually blue tape, but not always.

 

dgi

[LenRobertson]

The connector is usually folded back on the harness and held with a loop of tape.  In late cars that tape loop is usually blue tape, but not always.

 

dgi

Thanks! I didn't think of it as being seriously hidden. My eyesight is such I mechanic by feel as much as sight so I was feeling for the right shaped connector. I'll try the braille method on the main harness.

 

Len

[dgi]

I've also found it folded back on the radio/lighter branch, but it might not have been that way originally.  That car has some serious PO wiring issues.

 

dgi

[LenRobertson]

I found the connector right where you said it was - taped to the main harness with blue tape (up under the very top rear of the dash; needed a mirror to see it).  I doubt I would ever have found it without your coaching. Thanks again so much! I had to take the four screws out and pull the whole instrument cluster out of the way but that was easy enough. I have one always hot wire and one that switches on with the headlights so this must be the right connector.

 

The puzzlement now is the connector from the harness and the one from the tach both are female - essentially the same connector. No idea what year this tach is from. Maybe Datsun switched the male/female configuration of the connectors sometime prior to '72. I may be able to cut small brass strips or lengths of wire to connect the two and wrap them together with gaffers tape. I'll think of something.

 

Len

[LenRobertson]

It's Alive! :thumbup: I lashed everything together this afternoon enough for a test fire. Quite a thrill when the engine fired and the tach needle jumped to life. The guy I got the tach from told me it had been on his shelf for 15 years so I had my doubts about it. If nothing else I expected to have to switch the wires between the dizzy and coil because of wrong polarity but I didn't even have to do that.

 

I made short U-shaped jumper wires from #14 solid wire to connect my two female plugs together. I flattened the ends of the copper wire to a blade shape to slip into the plugs. I may come up with a better idea for that but it may serve the purpose if I tape everything up really well. I'm going to keep an eye out at Pull and Save for the correct male plug end if they might have been used on other model Datsuns.

 

Thanks again dgi. I know your tach write-up saved me a huge amount of time.

 

MikeRL411 - I did have to use #14 wire although I'm not happy about it. My local place didn't have #12 bullet connectors. I tried cutting some strands off #12 wire to get it to fit into a #14 bullet connector but gave up and used the #14 wire. But if I can find the small diameter bullets in #12 size I want to redo the wires out to the coil.

 

Finally, I can't find my dwell tach to check the accuracy of the Datsun tach so I may just buy a new one. The old one wherever it is is really ancient so it might be good to upgrade to one made in this century anyway.

 

Len

[LenRobertson]

I was looking for something on Dime Quarterly and ran across a 510 tach article. I thought I would post the link in case the information is of use to anyone, especially if you have a dead factory tach.

 

https://docs.google.com/folderview?id=0ByCvxnHNk90SYzc4N2E1MWEtMzg0MC00YTE4LTkxZGQtM2RjODA5ODA1YjU1&tid=0ByCvxnHNk90SMzIxZWIwYWYtYzljNy00ZGU2LWI3ODctYzRjMmE0MGY3NTA1   (Vol. 2, No. 4)

 

There is an interesting mention of using a resistor in the wire from the coil to the tach when using electronic ignition. I have no idea if this is necessary but seems easy to do. I don't have enough knowledge of electronics to know if there is a down side to running a resistor in the coil ground circuit. Anyone have an opinion?

 

Len

[GoGoGo]

I did a ton of research when adding my factory tach to my electronic ignition (matchbox) and the car runs/starts perfect. My problem is that my tach is 100% accurate even after I tried to adjust it on the back. It jumps around and generally shows a much higher reading than what the engine rpm is. I've tried reversing the wires, running a separate ground from the matchbox to the body, even adding a 1K resistor that I got off amazon (car wouldn't even start after adding that resistor). About to go back to running the stock ballast resistor and see what happens. 

 

Really wondering if ANYONE is running a stock (4-wire) inductive tach with a matchbox setup that has accurate readings. If so, exactly how did you set it up and run all the wires? Again, the car runs great, the tach shows activity but just isn't accurate at all. 

[dgi]

Really wondering if ANYONE is running a stock (4-wire) inductive tach with a matchbox setup that has accurate readings. If so, exactly how did you set it up and run all the wires? 

 

Yes, I am.  Wired exactly as described in the write-up I linked above.  I checked accuracy against my dwell/tach meter at idle, 1000, 2000 and 3000 rpm and it was as close as possible to judge.  

 

I also have a Smith's directly coupled tach mounted in the car and again they match closely at any RPM.

 

I have a second instrument pod with the factory tach that I used briefly while my "best" pod was being restored cosmetically.   I calibrated it to match my dwell/tach meter before installing it and it too matches the meter and the Smith tach.  Before calibration, it was off about 100-200 rpm across the range.

 

I suggest you check your wiriing against that in my writeup for the matchbox distributor.  And closely inspect the small circuit board's solder joints for cracking.  I've seen the ground joint cracked before and that tach jumped around alot until I repaired the joint

 

Good luck,

dgi.

[LenRobertson]

An update on my factory tach installation that may save someone else a bit of time and frustration.  I hooked up my tach using the plug from the main harness that dgi helped me locate. The power wire to this plug is  powered all the time -  it stays hot even with the key switched off (probably to power the clock}.  I had no idea if the tach draws  power with the engine turned off so I used this always-on for the tach power source. As I mentioned in an earlier post the tach worked fine on initial start up and I didn't even need to switch wires for correct polarity. But two or three days later I went to start the 510 and the battery was stone cold dead. I don't drive the 510 all that much and I knew winter was coming when I wouldn't drive it at all. So I just unhooked the neg battery cable whenever I parked it and all was good although inconvenient.

 

Finally a couple of weeks ago I tore into the dash again and switched the power wire to the tach to one switched by the key (radio power wire). The tach still is working great and the battery holds charge when parked.

 

Of course in the spirit of it being a Datsun another electrical problem had to appear as soon one was fixed - my temp and fuel gauges would pin on high all the time. I suspected the voltage regulator for the gauges and that turned out to be the problem. On the '72 510 the regulator is in the same cluster as the fuel and temp gauges. The regulator has a tiny set of breaker points that seemed rather burnt on my car. I considered gently running a bit of fine sandpaper between the points to clean them and that may have worked. But I had a spare gauge cluster so I just swapped that in and it is working fine now.

 

Len