Interesting electrical problem.

[Xenn]

Interesting electrical problem developed today.

76 280z

When off, my battery seems to be disconnected from half the functions, my Accessory seems to be dead (and thus my fuel pump that is wired into it) , my fuseable links are good, , battery connections are good, it seems like a wire is on the verge of dieing, the battery shows on the voltmeter sometimes, but when i try to put a load on it it drops to 0. When running, the voltage reads 8 and varies with rpm (im guessing its only alternator then) My question is, has anyone else had something similar happen? I'm thinking it is one of my fuseable links, just it doesn't look broken (and isnt fully yet), I just dont know if my voltmeter is wired into my accessory function, (it stays on when the car is off, but could be wired in before the ignition. Someone who knows the electrical system better than me where does it sound like a break may be?.

Also my accessory functions work when my car is running. I just didn't keep it running at one point, and now dont have enough fuel pressure to get it started again.

[Zed Head]

Possibly the ignition relay up by the fuse box. The Accessory circuit is powered through it. My relay was hot-wired straight from the ignition switch and my Accessory circuit didn't work until I replaced the relay. The internals of the relay were completely rusted away. It appears to be mounted in a spot that gets a lot of condensation or water when something leaks. Check page BE-6 in the FSM for the location.

[SteveJ]

When off, my battery seems to be disconnected from half the functions, my Accessory seems to be dead

That would relate to your accessory relay coil being de-energized when you turn the key to the OFF position.

(and thus my fuel pump that is wired into it)

Unless someone hacked into the wiring, no, the fuel pump isn't on the accessory relay. The fuel pump being off when the car is off is a good thing, too.

my fuseable links are good, , battery connections are good

Did you test the fusible links out of the car for continuity? How did you test the battery connections?

it seems like a wire is on the verge of dieing

How do you tell if a wire is on the verge of dying? Does it have a cough?

the battery shows on the voltmeter sometimes, but when i try to put a load on it it drops to 0.

Check this with a multimeter. Put the leads on the battery. If the voltage drops to zero when you put a load on it, the battery could be going bad. How old is it?

When running, the voltage reads 8 and varies with rpm (im guessing its only alternator then)

If the electrical system is running at 8 volts, don't run the car. You'll damage your ECU. Get your battery tested.

My question is, has anyone else had something similar happen? I'm thinking it is one of my fuseable links, just it doesn't look broken (and isnt fully yet)

You just said your fusible links were good.

I just dont know if my voltmeter is wired into my accessory function

No it isn't.

Also my accessory functions work when my car is running. I just didn't keep it running at one point, and now dont have enough fuel pressure to get it started again.

Get a good multimeter. Check your battery voltage as I described above. If it fails, replace your battery. Your fuel pump relay is NOT controlled by the accessory relay.

Edited March 18, 2012 by SteveJ

[Xenn]

Ignition relay sounds like a likely culprit, i get runoff from inside my fender Ive seen leak there.

I wired my fuel pump into my accessory because i couldn't get a new relay at the time and mine is dead, ive left it like that since because it does no harm to me. Accessory being dead meaning when i turn my key to acc, the coil doesn't become energized. Did not remove and test impedance of links, I made sure they were still connected, not loose, and didn't fall to pieces when stressed, they were, however very corroded, hence on the "verge of dieing". Checked battery connections to make sure they were tight and not corroded, battery is 3 months old.

The problem with the fuseable links is when they go, they burn out on the inside and usually dont melt the casing. I would just take my multimeter out there and go check them but the problem is being intermittent, when i let my car cool down (while i spent the last few hours looking up information on what happened) and went back out, the voltmeter read fine, and i was able to start it and idle it up to normal operating temp without any problems.

This happened when i did something i normally dont do, get on the freeway while my car was cold, i can understand that stressing the system, but even if the problem has gone away for the moment, it just means when what ever is going wrong, is soon to go out.

I just wanted to know where the furthest point forward in the electrical system that links both the voltmeter and acc and then work up from there, Ignition relay sounds possible, but i donno if it going out could effect my voltmeter, if not, then the problem is further back.

If its not that im think one of my links got unusually hot and broke the circuit, im just gonna replace my whole fuseable link box, im just wondering if this means its the time to do so.

I posted this yesterday but it didn't go up it seems, thank you auto save.

[Zed Head]

SteveJ gave a very good set of answers in his post. I just gave a brief one place to look answer. But I think that you might be assuming some things that are incorrect, thereby leading you to look in the wrong places.

The voltmeter in your car reads battery voltage all of the time, even with the key off. Voltmeters draw barely any current, even less than the clock, so it doesn't drain the battery.

You didn't really say that the problem was intermittent in your first post and it's not really clear what "the problem" is, besides having a battery that reads 8 volts sometimes. Assuming that the voltmeter is reasonably accurate, when it reads 8, it's telling you that there's a huge draw on the battery. Essentially a short circuit. That's not good. But, on the other hand, the voltmeters are usually inaccurate on these cars after 30+ years. Even so, if its' dropping to 8 occasionally, you probably have a loose wire somewhere shorting to ground. Odds are it's either the alternator charging wire or the main big battery positive cable, because any other wire would melt with that big of a draw on it. I would check those big wires for breaks or rubbing on the body first, and soon.

No reason for the coil to be energized on Acc. It's only energized at On/Run and Start.

Not clear what you mean by "put a load on it" and the voltmeter drops to zero. Trying to Start? Headlights on?

If you had a cheap volt/ohm meter you could test all of your fusible links and a bunch of circuits for power. Even a cheapie will save you a lot of time and money.

Anyway, there's a few more places to look, and some possibilities.

[Xenn]

I didnt say it was intermittent in my first post because it wasn't intermittent at the time, its only after i went back out after a few hours that the problem went away. The battery was reading 8 when the car was on and running (no charge light), and 0 when off, but the starter would still engage and get the engine running, though the voltmeter read 0.

As for my ACC, the ignition on a 76 looks like lock/off -> acc -> on -> start. So the reason i was so confused, voltmeter would read 0, i would turn my key to acc and my fuel pump, which is wired into it, would not come on, but my engine would turn over, and when it fired up, my alternator would keep my fuel pump running and my voltmeter would read 8.

Also, my car used to run at ~15 volts when on, after repairs, new battery, and some other general electrical work it dropped down to normal 13-14 when running, now its back up to ~15 so this problem might also be causing my car to overcharge my batt, could be unrelated though.

[Zed Head]

Maybe you have a bad voltmeter. I think that the voltmeter might read voltage at the external regulator. The wiring diagram from the FSM would tell you where to look. A hand held meter would be pretty handy to verify what's going on.

[Xenn]

Maybe, but it wouldn't explain the accessory loss though.

[SteveJ]

I didnt say it was intermittent in my first post because it wasn't intermittent at the time, its only after i went back out after a few hours that the problem went away. The battery was reading 8 when the car was on and running (no charge light), and 0 when off, but the starter would still engage and get the engine running, though the voltmeter read 0.

You should use a multimeter to verify your voltage readings.

As for my ACC, the ignition on a 76 looks like lock/off -> acc -> on -> start. So the reason i was so confused, voltmeter would read 0, i would turn my key to acc and my fuel pump, which is wired into it, would not come on, but my engine would turn over, and when it fired up, my alternator would keep my fuel pump running and my voltmeter would read 8.

Your engine turns over with the key in the ACC position?

By the way, the accessory relay does not receive power in the START position. This is yet another excellent reason to undo your wiring hacks before trying to diagnose your problems. (FYI, the other excellent reason to undo your hacks is that depending upon how you hacked the wiring, your fuel pump will probably still be pumping fuel after an accident.)

Also, my car used to run at ~15 volts when on, after repairs, new battery, and some other general electrical work it dropped down to normal 13-14 when running, now its back up to ~15 so this problem might also be causing my car to overcharge my batt, could be unrelated though.

What repairs & electrical work? How are you measuring 15 VDC? Under what engine speeds?

Here is what I suggest:

Make a timeline of the issues with your car and the work you have done on it. Don't spare the details. Organize your thoughts. You'll get better suggestions.

As I said before, the FIRST thing you should do is repair your hacks. You might have one problem, or you might have several. It's difficult to tell at this point. I have some suspicions, but I'll wait until you have the chance to provide a clear timeline.