Signs of a bad harness?

[FastWoman]

... or if you want to roll your own, read deep into this thread of mine, and you'll learn all about maxifuse upgrades AND headlight relay upgrades in a '78 (probably very similar to your '77):

http://www.classiczcars.com/forums/showthread.php?t=35588

The schematic for my relay modification is in post #35. Total cost was less than $10, as I recall. I have to agree that splicing into the wiring harness is completely safe if you do it well. Crimp your connections, sweeten with solder, and then heat shrink. If you do this, your connections will actually be superior to the original Datsun factory connections. If you just do crimp connections, your connections will be similar to Datsun's, except fresher.

If your idea of splicing is shaving off the insulation, twisting wires together, and then wrapping up with electrical tape (or even using wire nuts), then definitely DON'T do it.

[SteveJ]

The 1977 came stock with the external regulator. You could look at the spot where the external regulator should be to see if it's still there and plugged in, if you want to be sure of what charging system you have.

That is based upon the assumption that the person who put in the new alternator knew what he was doing (provided the alternator has been replaced at some time). If you get an alternator for a 280Z from the parts store, you might get one with the internal VR or you might not. There are plenty of opportunities for error.

[Zed Head]

I agree, I mentioned it mainly for his own future reference so that when he goes to the parts store for an alternator he can ask for the right one.

I was also going to mention that the external regulator can put out up to 15.6 volts, adjusted correctly, depending on the temperature according to the FSM. They are kind of an odd mechanical device. I was already over my word limit though.

After looking at FW's diagram in her referenced rely thread, I also realized that he might have just blown the fuse, since the headlights are split and fused left and right. The first thing I would do is check the fuse for that headlight, then check the circuit and headlight. A new headlight shouldn't blow from high amps, before the fuse does.

[SteveJ]

I was also going to mention that the external regulator can put out up to 15.6 volts, adjusted correctly, depending on the temperature according to the FSM. They are kind of an odd mechanical device. I was already over my word limit though.

After looking at FW's diagram in her referenced rely thread, I also realized that he might have just blown the fuse, since the headlights are split and fused left and right. The first thing I would do is check the fuse for that headlight, then check the circuit and headlight. A new headlight shouldn't blow from high amps, before the fuse does.

Mechanical adjustment is correct on original regulators. I think most any produced in the last 20 years or so are solid state. Those boxes are sealed tight and non-adjustable.

You have a point on the blown fuse. Ty - was the headlight completely out or dim? If it is dim, that means the other headlight is backfeeding through it.

On the other hand a headlight can blow from overvoltage, and the fuse will go through unscathed.

[tymarbry]

Here is the car with the right headlight in the picture dimmed horribly. It was originally the brighter of the 2.

Im sure the fuse for both headlights are fine. Im going to check it tomorrow along with the volt/ohm test if my ohmeter is working.

[SteveJ]

Did you try switching between high and low beams? Frequently with a bad headlight, only one element goes bad with the dual filament bulbs, so you still have one or the other.

As for the fuses, NEVER trust a visual inspection. Pull the fuse and test with an ohmmeter. If it is more than about 0.2 ohms, replace it.

[tymarbry]

Switching between high and low beam makes no difference in the right headlight.

The working headlight does still have a high and low beam though.

[SteveJ]

And the fuse?

[tymarbry]

Havent messed with the fuses or the ohmeter yet, Im waiting for the weather to straigten up.

[tymarbry]

Fuses are fine and I ran the volt/ohmeter on the headlight plug and it runs at 13.6/13V when car is running. So I guess it was just bad luck with a bad bulb.

Im still awaiting my H4 Lights from autopal to come in.

[Zed Head]

You have a point on the blown fuse. Ty - was the headlight completely out or dim? If it is dim, that means the other headlight is backfeeding through it.

If the dim light doesn't change when going from high to low then SteveJ's clue here looks promising. The headlights share a common ground. The bright light might be grounding through the dim light to a short on the other side of the dim light. You probably have a "partial" short (high resistance short circuit) in the area of the fuse box.

I would crawl up under the dash by the fuse box with a volt/ohm meter and do some investigating at the headlight circuits.

[tymarbry]

I have no idea on where to start with that honestly. Im not good at electrics at all. I hate them.

where are the headlight circuits located at under the dash?