1978 280Z electrical gremlins

[mdbrandy]

Well, all of a sudden this morning, I've developed a fairly serious electrical gremlin in my 280. I know it's pretty tough to diagnose on the forum from reading about everybody else's gremlins, but I wanted to post the symptoms to see if anyone recognizes the problem.

Parked last night. No problem. Came out this morning, started right up, and the radio acted like it had lost power (no memory). Then I noticed that the clock had stopped too (and yes, it had always kept perfect time before). While the car is on (engine running), all is fine. Volt meter shows correct voltage, all lights work. As soon as I turn the key from On to acc to turn the car off, the radio loses power, the dash goes dark, and all rear lights go off. There is also a loud relay click at the passenger kick panel at the same time. The headlights still work. If I turn the key back to the on position (but don't start the car), all guages go to their appropriate positions EXCEPT the voltmeter, which stays at zero until I start the car, at which point it goes up near 15V and all is well again. Before today, the voltmeter always just dropped back to 12V or so when I turned the car off. In the ACC position, there seems to be no accessory power at all, and no lights except headlights. I'm assuming the relay I'm hearing is the ignition relay, but I don't know yet.

The only "smoking gun" is that last night after parking the car, I replaced the two plastic covers over the fusible links in the engine compartment. I didn't start the car after I did that.

After studying the electrical schematics for a while, I'll be taking a look at the area around the fusible links first, but I can't imaging what I might have done. If I had broken one of the links, I would think that something would be always off instead of working when the car is running.

Oh, and I should mention that this morning while driving, the radio died 3 or 4 times randomly and immediately came back. Didn't happen at all driving home tonight.

Any insights or recommendations would be very welcome before I start digging into circuits, grounds, etc.

Thanks.

[TomoHawk]

One of those fusible links goes to the dash and interior lights. Forget which one.

[mdbrandy]

Originally posted by TomoHawk

One of those fusible links goes to the dash and interior lights. Forget which one.

Cool. I'll certainly check that out. But if I broke it, or loosened it's connection, why would everything work in the 'on' position of the ignition, but not the "acc" posiiton? That'll probably take some schematic reading...

[TomoHawk]

The power going through the fusible links comes straight from the battery. Because of some wiring redundancy, after you start thye engine, the power from the alternator finds it's way on different wires.

[mdbrandy]

Thanks Tomohawk. Looks like it is the fusible link. There is one maked "ACC", and when I wiggle it, the lights that are out flicker on and off, and when I put the continuity meter on it (off the car) and wiggle it, it varies between a few ohms to infinite resistance. So I need a new link. I see sets on e-bay all the time, and I'm sure Chloe can probably get them for me, but does anyone know if this is something you can get at the local auto parts store? Or even at Nissan?

[TomoHawk]

I has one that looked ok on the outside, but was broken inside, until I pulled on it and it broke apart.

Fuse links are a special order item from the dealer, MSA has them individually, and I dunno what to think about the eBay ones.- only get the unused ones, of course. Those thinks are too important to not have complete trust in them.

[mdbrandy]

Originally posted by TomoHawk

I has one that looked ok on the outside, but was broken inside, until I pulled on it and it broke apart.

Fuse links are a special order item from the dealer, MSA has them individually, and I dunno what to think about the eBay ones.- only get the unused ones, of course. Those thinks are too important to not have complete trust in them.

This one actually looks fine. Doesn't break apart, seems pretty solid. But wiggle it and it appears to have a small internal break.

Bummer on the special order. I'll pull one off the wiring harness from my parts car and see if it works while I order new.

Thanks.

[TomoHawk]

When I inquired at the dealer I was told about a week for delivery. MSA could get them to you just as fast, and you could get only the one(s) you need. My dealer had to order the whole set. Your dealer might be different. Your call.

I'm looking into the books to see what the ratings were. I think I saw it somewhere, but didn't have time to Xerox.

oops- photocopy.

[mdbrandy]

Originally posted by TomoHawk

I'm looking into the books to see what the ratings were. I think I saw it somewhere, but didn't have time to Xerox.

oops- photocopy.

I have the factory manual, and they seem to be rated in terms of the cross sectional area of the wire. There are three different sizes listed, and visually, this is by far the biggest one.

[TomoHawk]

tjere has to be some correlatiopn between the cross-section and some kind of current rating. How else would the engineer select one? color?

[mdbrandy]

As long as the material is the same for each of the link wires, then the resistance of the wire will be proportional to the length and the cross sectional area (i.e., the resistance per unit length will be proportional to the area). They are color coded too, though.

[mdbrandy]

Oh, and for reference, the three listed by color and cross sectional area are:

Black 1.25 mm2 (0.0019 in2)

Green 0.5 mm2 (0.0008 in2)

Brown 0.3 mm2 (0.0005 in2)

They don't provide any resistance values to go with the area.