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PostPosted: Mon Jun 30, 2014 2:47 pm 
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Location: CT
An inline bulb is just a test light. It (usually) has an indestructible lamp in the middle of two leads, one Pos, one Neg. When you complete a circuit (make electricity flow thru the tester) the lamp lights up. You can buy them at any auto store, but they're easy to make, too.

Those of us who drive Zs actually already have an inline bulb under our hood (altho they're not meant for this kind of use). The Underhood Trouble lamp on the inside fender well works exactly the same way as an inline test lamp does. When it's in its socket (normal position) it's grounded, so all you have to do is flick the switch and it comes on.

BUT, if you unscrew the lamp and pull it away from the base, the 4ft of coiled green wire inside allows you to move it all around the engine bay. With the switch flicked "on", any time you touch the metal hook to ground, the lamp will light.

It's usually meant to hang from the open hood latch, to give overhead flood lamp effect and light the whole engine bay. I've recently spoken to two Z owners who never realiZed their trouble lights were meant to do that. Searching Google images, I can't find any photos of the light unscrewed and extended, so maybe this whole generation has forgotten that this handy little lamp is meant to travel around the engine bay??
The bulb/cap unscrews with a 1/4 twist. Pull it away from the housing and there's 4ft of wire wound around a hook. Pull the lamp to anyplace and ground the hook. The lamp lights.


Attachments:
File comment: Good example of a simple in-line test lamp, also used as a voltage tester. When current is present, the bulb lights.
In line test light.jpg
In line test light.jpg [ 23.96 KiB | Viewed 2197 times ]
File comment: Our little friend
Datsun Z trouble light.jpg
Datsun Z trouble light.jpg [ 33.67 KiB | Viewed 2198 times ]

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PostPosted: Mon Jun 30, 2014 6:26 pm 
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Joined: Mon May 19, 2008 8:17 pm
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Location: Colchester, Ct
It's a pretty simple process. All you need to do is disconnect the ground wire to the battery and introduce a low voltage bulb between the disconnected ground wire and the negative battery terminal. A simple light socket with two leads is the best way to go. By making this connection, you have completed the original circuit through the battery with the exception of having a light bulb inline. If power is being drawn from the battery, the light bulb will glow. Then all you do is methodically remove fuses and/or electric components until the bulb goes out!!

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PostPosted: Mon Jun 30, 2014 10:18 pm 
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Thanx Uncle Phil, you're a LOT smarter than you look!!! :lol: :thumbs_up:

Q: Now, if that Z has two or more short circuits (grounded circuits), the light will not go out when any single fuse is pulled, because current will still be flowing thru the other grounded circuits. How does he check for multiple shorts?

A: He pulls ALL the fuses out, then replaces them one at a time. If the light stays out when he installs a fuse, that circuit is good and he can leave the fuse installed. But when the light goes on, he's found a grounded circuit. He removes that fuse again and moves his test to the next empty fuse slot. After he has checked each fuse, the empty spaces show how many 'leaks' he has in his electrical system.

PS ~ also, batteries can self-discharge across their terminals if the top of the battery is dirty enough to conduct a current. Anything conducive will work; water and grease are most common. Mixed with a little dirt, they can hide and look harmless. But it sounds as if your 'leak' is external here.

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PostPosted: Tue Jul 01, 2014 6:03 pm 
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Location: rhode island
You can also use a 194 bulb if you had to. (side marker bulb) As far as Diodes, they are a one way electrical gate, if they go bad, not a one way gate no more and electricity can drain back if that makes sense. Frank, I love those under hood lights.......Now that's engineering.


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PostPosted: Tue Jul 01, 2014 6:47 pm 
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Location: CT
Well Kent, by now you probably think we're all craZy in here. You ask a simple technical question and we all start talking amongst ourselves like a bunch of good ole boys around the pot bellied stove with our boots up on the barrel top.

No offense intended, we're not ignoring you ~ all this chatter is intended for your digestion. Just everybody re-living his own experiences with your particular problem. This happens a lot in here! :lol:

Lean back in your chair and put your boots up with ours.
And tell us what catches fire or explodes when you follow our advice! :lol:

Frank

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PostPosted: Fri Jul 04, 2014 6:13 am 
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Why Frank...Do you have a Pot Bellied Stove and a Barrel we can all put our feet on......and drink from of course.......


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PostPosted: Fri Jul 04, 2014 6:15 am 
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I have a feeling you do this on occasion. :shock: :D :P


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PostPosted: Fri Jul 04, 2014 8:49 am 
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I have removed two fuses and the battery holds a charge now for several days. The issue now will be to chase down the problem in one or both of those circuits. I still think the trunk or hatchback sensor is one of the problems. It attaches to a single wire, and whether or not that wire is grounded does not seem to make a difference. If anyone knows how to disable that sensor I would appreciate it. Taking it out of the circuit doesn't help, but pulling the fuse for the circuit does help.


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PostPosted: Fri Jul 04, 2014 10:50 am 
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You should suspect a short or even a dead ground anywhere along the circuit wire, and possibly even at the fusebox itself (that has happened to me on a different car). Because you don't mention blown fuses I would suspect a mild short rather than a dead-ground. Check for current at the end of the circuit (at the actuator button) to see how much flow you're getting back there. If it seems less than normal, you have a short somewhere along the line btwn the fusebox and the actuator button.

If you read full current and voltage at the soldered button connection, you should suspect the button itself. Disconnect the button and tape the end of the wire. Leave the fuse in and try Uncle Phil's in-line light test at the battery terminal. If the lamp does not light, you've isolated the button which was your problem. If the lamp lights, the problem is elsewhere along the wire.

Be suspicious of anyplace on the car body where a hole has been drilled for an electrical device. Rust loves holes (sometimes makes it own!) and a bit of corrosion around an electrical hole (door sensors, alarm buttons, etc) can allow lazy electrons to run back home (short out) before their work is done.

Consider electricity as 'lazy'. It wants to return to ground as soon as possible, with the least amount of resistance possible. If rust or a frayed wire or an exposed soldered connection provide a bridge back to ground before the current has completed its work, the current will take that shortcut.

It's also easier to picture electricity inside wires as if it were pressurized water flowing thru hoses. If there's a leak anywhere in the hose, the water will spray out there, lowering pressure and reducing the amount of water flow you get at the end of the hose, where the water was supposed to do its work. If the leak is big enough, ALL the water will spray out there and you'll get no flow at the 'work end' of the hose. Also remember most of your 'hoses' (wires) are connected to other 'hoses', so just because the hose you're examining is OK, doesn't mean a leak in a connecting hose won't steal water from yours. Your alarm button might be OK, but the leak is happening somewhere else in the alarm system.

As you probably already know, the body wires on the S30 cars run from the dashboard to the rear of the car thru two bundled electrical looms which lay btwn the seats and the doors. They're fairly easy to get at and unwrap. You can be scared by some of the rust you find in there if you've never unwrapped them before. Clean them, inspect each wire carefully, and re-bundle them with clean electrical tape when you're done. I found water in mine, while the car interior was completely dry. Anyone who has stripped an S30 down to the metal during a restoration can tell you weird stories about these interior wire looms.

Each wire has its own color code of course, so you can trace it when it emerges from some loom where you can't follow it visually. That allows you to test both ends with a multimeter, checking continuity and resistance.

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PostPosted: Sun Jul 06, 2014 6:32 am 
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I believe when you lift the hatch the door light comes on in the console. If not good sign that sensor is not working and could be shorted.


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PostPosted: Sun Jul 06, 2014 10:46 pm 
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Joined: Sat Jun 01, 2013 5:38 pm
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Location: Orange, CT
Excellent response Frank.
However the line test tool you referenced looks like a household 120V AC tester.
Here's a little tool I use and is invaluable when searching for short circuits.

http://store.snapon.com/6V-and-12V-Circ ... 44276.aspx

Snap-On is pricey, there are way cheaper ones on the market that do the exact same thing.
Probably Harbor Freight has one for less than $5.
I personally have 2 Snap-On units and they send me new bulbs whenever they go out. Which does happen ocassionally.

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PostPosted: Mon Jul 07, 2014 1:10 am 
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Yup, thanks. I agree, the only picture I could find was one of the household current tester. I have one of those units here at home and it's handy for checking that I indeed turned off the correct circuit breaker before I stick my fingers into the wall plug I'm replacing, etc. I used the only pic I could find to demonstrate any example of an in-line test light. Altho the one I showed actually responded to 12v DC on the Z when I tried it last year :lol: . It wasn't supposed to work, but it did!

I normally use a cheap multimeter which I actually carry around in the back of the Z.

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PostPosted: Tue Sep 16, 2014 11:18 am 
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Joined: Tue Sep 02, 2014 5:10 am
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Location: Waterford, Ct.
I had the same issue on my 86' 300zx. I'm not the one who fixed it but it's fine now, I was told it was a loose wire to the fuse box. Hope that helps, I'm at lunch and didn't have time to read through all the posts.
Colette


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