Zed Head

It might just be that the parts changed but the diagrams did not. There are other diagrams that don't keep up with the actual parts. Or, the switch has been replaced along the way with a newer part. Trust but verify, I guess.

Thanks for the comments cgsheen1. I'm just trying to figure out things using the wiring diagram.

Nice video. Now I'm left wondering if a 72 will Start with the wires switched. The switch diagram shows just one power source for the coil for either Start or On, there should be no power there at Start if the wires are switched. The 71 diagram shows all 5 pins powered at Start though. If we only had the 71 diagram there wouldn't really be a discussion. Anyway, looks like a stuck or bad tachometer.

The question isn't "will it run" it's "will it start". The later switch diagrams, like the 72 diagram from EuroDat above, show separate power circuits to the coil. A Start circuit and a Run/On circuit.

You can just use your meter and disconnect the starter solenoid wire so the engine doesn't turn (for the quiet). See which wires have power at each key position.

It might start as soon as the key is let back from Start to On, wired that way. I recall some old posts about early ignition switches being different. There was discussion about losing power during starting, to radios or AFR gauges or or Megasquirt controllers or something.

Here's a 72 switch from a diagram that EuroDat created. Doesn't show B but it can be assumed, I guess. Start and On/Run are powered separately.

Here's the 1976 scheme just for comparison. Accessories off for Start. R must be the resistor bypass. Never really looked at it when I had mine. It's EFI though so IG has to maintain power.

That's interesting. It implies that 2 and 5 are both powered at Start, otherwise there would be no power to the coil at Start if the wires were switched. I thought that 2 switched off at Start. The diagram seems to show that every pin is powered on the bottom position which should be Start, which doesn't seem right. Usually accessories are disconnected for Start. 5 is shown as bypassing the resistor which should be the Start circuit. Kind of confusing. Switching the wires would bypass the tach and the resistor at Run. Makes sense that the engine would run but the tach would not work. Edit - looking more closely at the grainy drawing I think I see small circles at 1, 3, and 5. Matching AnvilZ's post below. Doesn't answer the question though. ,

I did not watch SteveJ's video (no offense SteveJ) but if you have tested everything and confirmed that the wiring through the loop on the back of the tach is correct then you end up with "tach is bad". They do crap out after 40+ years. I had a bad one in my 76. I think that there is a place or two that can rebuild them. Have you confirmed that the needle is not stuck? If you take it out you can take it apart and do some cleaning. People have had success doing that. It's a common problem. Just watched your three videos. The tach is probably not destroyed. It's just not working. It's fixable. You might post another thread titled "Who can rebuild/fix my tach?". I can't remember who knows but they are out there.

If you saw continuity, then never mind.

You might take those measurements again, following SteveJ's instruction. Make sure that the current is actually passing through the loop. You could also take a measurement at the tach plug to make sure the voltage is getting to the tach. Then you'll know for sure.

You should put your videos on youtube.

So, what, in detail, does the tach do and not do? Does the needle twitch at all when you turn the key on or start the engine? These old tachometers fail often and in many different ways.

I found an old thread. Pretty much original owner. So, external regulator, old alternator. The VR's go bad eventually, but usually go high voltage. Might just be a bad alternator. Could even be a bad connection on the back of the alternator. Pull them off and clean them up and see if things are better. You'll need a meter like SteveJ says. This is a sign that there's no alternator current -

Can't remember what car you have. and if it's been modified. Things changed over the years.

The prices are trending up. That 300K one really screws up the resolution. I filtered it out. https://bringatrailer.com/datsun/240z/?q=240z

Both of those local coils would probably work just fine. That's a wide spec on the Duralast coil, but it will probably be in the middle at about 1.5. Even if it's a little bit low, that's not a huge difference. Maybe a little extra heat but worst case it will probably just last 50,000 miles instead of 100,000. I'd buy one of those two coils and just use it with your ballast resistor. You'll probably want to check the size on that older Ford/GMC coil if you use that one, it might not fit well. But it should work with no problems once you get it mounted. If you have a meter you could take it to the store and verify primary resistance before you buy if it worries you. Secondary is not as important for longevity, I wouldn't worry too much about that measurement. Just for fun - https://contentinfo.autozone.com/znetcs/psb/en_US/2/0/27/c831_coil_specs.pdf

I never did but probably should have. I think that I used to over-torque my aluminum wheels and was distorting the rims at the seat, squishing it there. The lug nuts used to get stuck in the holes and I'd use a rat tail file to open them up a little. Probably Not Good. Now I have a Ford truck that specs 150 ft-lbs per nut on steel rims. So I bought a wrench and used it. That's a lot of torque.

https://www.gorilla-auto.com/replacement-keys "A Wheel Lock Registrations Key is required to identify the unique key for all Original Gorilla Wheel Locks, X2 Locks, Gorilla Guard or Small Diameter Wheel Locks. Replacement Small Diameter Lug Nut and Hex Lug Nut Sockets can also be ordered using Key Registration Number or Part Number stamped on your Gorilla socket. Why do I need my Wheel Lock Key Registration Number? We are the leading wheel lock manufacturer for good reason, your unique wheel locks and key are nearly impossible to identify through simple visual inspection. Your unique key/lock combination is one of thousands of possible combinations which means your investment is protected."

It's done by computer, and it's not a mold, it's a milling machine. What good is a lock if one key fits many of them? That would be insane.

You must have good eyes. Can you share the photo? Hope it works...

How do you know? The splines are of varying width. It's not just the number nine.