As far back as I can remember, accessory plugs were wrapped with blue tape to identify them, but I have also have seen yellow tape used, this may help you in locating them.
Also later model vehicles that had electronic ignition used a "tach resistor" in the circut to get it to function. If yours requires one and it's not there the tach won't work no matter what you do. Check a wiring diagram for your year and model to be sure.

The guy who owned the car before me had done some weird stuff to the ignition, so I think you're right in that it may be pulled apart right now. I'll check tonight if I see anything under the hood. I didn't see anything when I checked under the black box next to the ignition, but I'll check again to be sure. Currently my dash is all ripped apart but I need the car for tomorrow so if I can't find anything tonight, I need to wait until the weekend. I apologize in advance if I can't give an update for a while.

That tach was the hardest thing to search for in the Pacific Northwest. After my car was totalled, I sold it to someone in the Seattle area for $50.
When I pulled it from the junkyard I cut the plug off the wire harness but found out that the plug was just a standard option on the wire harness because car had one.

Good work so far. The 4-pin connector might be under-hood and i think a likely source of the trouble. In the last 45 years somebody may have pulled it apart -- i seem to remember it is the test connector for the ignition

it may also be covered with tape. Are there any bulges in the harness under the hood?

at a guess perhaps somewhere near the firewall or under the black metal box next to the coil

So apparently the lamps did work and I'm just an idiot. However, the tach isn't giving off any readings. I think I've pinpointed the source of the issue though. I ran a multimeter on continuity setting from the black and white wire to both the negative terminal on the battery and the negative on the ignition coil, which should all be connected. They are not. I have now, however, narrowed it down to two possible issues. All data I'm about to state has been tested with a multimeter, but I'm not exactly proficient at using it, so it may be flawed.

The image below shows what I have tested. The wire highlighted in blue is the one giving me issues. The ignition coil to first coupling (drawn with green arrows) are working as far as I have tested. However, from the first coupling to the mini harness has a discontinuation in it somewhere (drawn with red arrows). There are 2 other couplings between the 1st coupling and mini harness, but so far I have not been able to find them (circled in red). I have spent hours trying to follow wires and it has gotten me nowhere. If anyone happens to know where they are it would be greatly appreciated.



Worst case scenario I'll try and run a new wire from the negative terminal of the ignition coil into a splice on the B&W wire in the mini harness that's in the dashboard, but I've never done anything like that so I'm hesitant.

https://imgur.com/pGzRhL8 (higher quality image)

You were right about where the 6 pin connector was. For some reason it was sounded by tape so I couldn't see it. I just hooked it up and unfortunately it didn't work. The lamps didn't work either. I'm in the process of learning how to use a multi-meter so I can find the source of the problem.

here's photos from eBay, looks like a good unit. And best of all it has the adapter harness included

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  LHD USA tachometer (top with canted tab).jpg (105.73 KB)


  LHD USA tachometer (back).jpg (99.94 KB)


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here's details about the 6-pin connector on the 1976-1978 B210 USA

As long as the tach has the mini-harness still attached, it will fit your car

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  LHD USA tachometer (back) WIRING MARKED.jpg (118.33 KB)

about the 6-pin connector
* has locking tabs (nubs on the dash connector)
* has two round corners, so not a simple retangle
* has a slot in it after the first two pins (dash connector) to fit the divider (in the mini-harness connector)

after thinking about this ...

i think this is the 6-pin connector in your dash photo

It's tucked out of sight in your photo, but those are the color wires


took some time to review the photos and old threads ... been a long time 2012 since we discussed it

Quote:The guy who posted that photo -- nine years ago -- never figured out the wiring harness. He bought a used tachometer and it came without the tachometer mini-harness, and only had the three tach wires



One wire had an adapter on it for some reason

He said what do I do with this? couldn't find any "matching" wires in his dash. Eventually he didn't use the factory wiring and he ran new wiring from the dash out to the coil and got it working

That is one way to do it. As long as it is a LHD tachometer, it will bolt in. The dash wiring can be used -- or the three tach wires can be connected manually to various points of the car like Ground, 12V and the coil-Neg post. If you have electronic ignition (1976 CAL) then instead of the coil it connects to the underdash "black box"

In his 1977 B210, here is the 6-pin connector (which he didn't end up using)



6-pin connector colors? looks like
BW L (Black w/White stripe, Blue wire)
RY B (Red w/Yellow stripe, Black wire)
GY R (Green w/Yellow stripe, Red wire)

Now these colors DO NOT MATCH the tach mini-harness connector colors. Yep, that's how Datsun did it. But two of the three main wires match colors (BW - tach signal, B - ground). The tach's signal wire (BG) connects to the mini-harness BG then on to the Dash Harness (probably the GY wire). The red and blue wires are for the gauge illumination (Blue (L) wires are typically LAMP wires on Datsuns)