NewZed

The headlight low and high beams are controlled on the ground end of the circuits. Sounds like you have a short circuit to ground on the high beam circuit. That would also cause the high beam indicator to glow. Both circuits get power as soon as you turn on the headlight switch. The switch at the base of the turn signal stalk determines which circuit, low or high beam (short or long), gets grounded.

Those odd things. Forgot about those. I've seen it proposed that they are meant to stop engine movement if the car gets hit from behind or hits something. Seems more like they might be meant for ease of engine removal and replacement. Here's a place that might have some pictures. You'll have to browse. https://bringatrailer.com/datsun/280z/

Imagine the engine in the car with its tilt and choose accordingly. The vertical side will be the short one.

Beside the fact that it's a sign that the damper rubber has been damaged and/or is failing, 1/4" will almost certainly throw belts at higher RPM. I damaged a damper pulley on an old muscle car and it used to throw the power steering pump belt when doing typical high school kid stuff in the rain. Pretty exciting, but it was a good arm workout when it happened.

If you pulled on the rim of the pulley you pulled on the rubber. Might have damaged it. 10 thousandths is not 250 thousandths. Not clear what your first post meant, with the 1/4 inch.. Anyway, if your timing marks seem off that's a sign of a failing damper also. Good luck.

Both of those are not right, but the damper is most wrong. Damper rubber failure is not uncommon on these old engines. The crank pulley is mounted on the damper, aka harmonic balancer. https://www.rockauto.com/en/catalog/nissan,1976,280z,2.8l+l6,1209226,engine,harmonic+balancer,5512

1976 is different so my first comment might be off the mark. Here is 1976 -

There's a connector on the way to the gauge. If whoever cut the harness has been inside the car you might want to check there. C-1, it's blue. Also, it might be that in 78 they ran that wire up from the passenger side. My comment above is about a car like my 76.

Might help if you showed a picture of what you're dealing with. If the engine was in the car and the harness intact it would be in the bundle that runs along the top of the intake manifold. A yellow wire, according to the wiring diagram in the Service Manual. Here's a web site with pictures. And what I think is the main bundle that then splits up. p.s. I don't think it's part of the EFI harness. The two wire water temperature sensor is but the one wire temperature sender, for the gauge, is not. https://bringatrailer.com/search/?s=1978+280z

Download a Factory Service Manual and wiring diagram from the site below. The headlight low and high beam are controlled by the ground circuit at the turn signal stalk. Both circuits have power when the switch is turned on but only the one that is grounded will light. Seems like you might have a short to ground on your high beam circuit. https://www.classiczcars.com/files/

Looking back at your first post I see that you do have an aftermarket cam of some sort. Is the cam timing adjustable? Might be too advanced. Of course, the Isky cam will probably be correct, but you might have possibilities already there. https://help.summitracing.com/app/answers/detail/a_id/4706/~/advancing-%2F-retarding-a-camshaft

The basic subject of this thread was covered pretty well years ago. The thread is kind of buried in the L series sub-section under Powertrain FAQ's.

Kind of extreme from a guy who has no apparent experience building engines. I assume that you read something on the internet and absorbed it as your own. You were asking how to install a turbo just a few days ago. Nothing wrong with questioning somebody's comment but if you're going to fake expertise try to do a better job. Better yet, just don't. And there's no need for the insulting tone.

BRAAP did a lot of studying on the NA engines. He summarized his knowledge in the thread below. The third post and more might be relevant to your problem. I assume that your boost gauge is in the plenum. "Boost" is caused by restriction to flow. He also has quite a bit about port work. If the runners and ports are restricting flow a different cam won't help much. Not an expert. p.s. 270 HP from a 168 cubic inch engine is a lot. 1.6 HP per cubic inch. At the rear wheels. Have you thought about the bottom end, and durability? Solving your problem might be the end of the engine. Good luck.

Let it load upside down. People can manipulate it.