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Hello everyone I had a question about voltage. I am a newbie when it comes to wiring and electrical but I did my research and read the forums. 
 

I have a 1977 280z and it looks like someone’s been in there trying to figure out the issue. Missing bolts etc. anyways with my multimeter I tested the coil and the resistor and voltage. 
 

the voltage was off.. well there was none with the key on the on position, testing on the first terminal on the resistor. so this is what I checked, I went to the battery and checked the cables those are good, car turns over. I looked at the wiring diagram and found the black and white wire that leads to the ignition relay. That wire read at -12.45 volts. As if I I had my wires crossed on my volt meter. Then I searched and found the red and white wire that leads to the battery. And again same thing that wire read -12.45.. I went back to the battery terminals and tested there and that was +12.45. Sooo my question is why is it reading as negative in the wires? Is this normal? Andy ideas as to why the black and white wire that goes to the resistor is getting no power.. 

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The only thing that comes up is your car has the Plus on the chassis.. the battery cables are on the wrong pole? they are different diameters so the cables are on the wrong spot.

Does the Plus go to your chassis? and the minus go's to the starter? 

The ground should be minus and the big plus lead should go to the starter! Pictures show more than words! I would like to see whats the case ..

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14 hours ago, 280zdude said:

I went to the battery and checked the cables those are good, car turns over. 

I looked at the wiring diagram and found the black and white wire that leads to the ignition relay. That wire read at -12.45 volts. As if I I had my wires crossed on my volt meter.

If the starter works correctly, and the battery measures correctly, it seems likely that you might be placing your probes in the wrong areas or somebody has reversed some wires.  

Go back to the source of the power to the coil and see what readings you get.

image.png

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I responded to your other post: 

As I said in the other thread, you are leaving out important context of HOW you are measuring the voltage. Where are you placing the positive and negative probes?

Adding to this thread, what is the voltage from the positive battery terminal to the body? What is the voltage from the negative battery terminal to the body?

I have never heard of anything good happening to a 280Z if the battery terminals are swapped.

Here is an example of checking for voltage at the coil. For your issue, you could put the positive probe at the black/white wire at the ballast resistor. 

 

 

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Ok thanks for the reply’s I’ll do everything you guys are saying and try to take pics. and get back to you! 


At the coil there is no voltage. Red prob to the + of coil and black probe to strut tour. 
 

at the ignition switch. I connect the red and white wire to the red probe and the black probe to the body such as the door hinge bolt any bear metal under the car. 
 

Same goes for the black and white on the ignition relay. 

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9 hours ago, dutchzcarguy said:

The only thing that comes up is your car has the Plus on the chassis.. the battery cables are on the wrong pole? they are different diameters so the cables are on the wrong spot.

Does the Plus go to your chassis? and the minus go's to the starter? 

The ground should be minus and the big plus lead should go to the starter! Pictures show more than words! I would like to see whats the case ..

 Ok took some photos of the battery and the wires leading to the starter 

image.jpg

image.jpg

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Is your battery connected backward?  I can't tell where the cable goes at the circle I drew (weird how pictures are always fuzzy in the area that matters).  Not sure how the starter can work backward but maybe it can.  It's a DC motor and solenoids are just magnetic coils.  I wonder if your engine is spinning backward.  That would be a new one, never heard of it happening.

The positive cable should be connected to the solenoid, the small cylinder on the starter motor.  The negative cable should be connected to the starter mounting bolt.

image.png

 

Edited by Zed Head
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Your battery cables are probably swapped. Again, the way to confirm is to measure voltage from the positive terminal of the battery to the body and from the negative terminal of the battery to the body. If the battery is connected properly, you should see 12VDC from the positive battery terminal to the body and zero from the negative battery terminal to the body. 

Nothing good ever comes from crossing the streams...

 

Edited by SteveJ
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Yep, your battery cables are backward.  Hopefully nothing has been damaged.  

The cable that your finger is pointing to should connect to the - post on the battery.  Negative.  Ignore any cable or wire colors around the battery.  Red and black are meaningless.

 

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So new news I just connected the negative terminal to the the red probe and the black prob to the body and got negative 12 volts but when I did it the other way I got nothing.

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2 minutes ago, Zed Head said:

Yep, your battery cables are backward.  Hopefully nothing has been damaged.  

The cable that your finger is pointing to should connect to the - post on the battery.  Negative.  Ignore any cable or wire colors around the battery.  Red and black are meaningless.

 

I see can anyone send me a pic of how the smaller cables are connected. Hopefully I bought the car like this there were a couple blown fuses but only for the lights and what not. Hopefully not wires have been shorted in between 

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Making progress.  The backward battery is one of those Nissan pitfalls that catches many people.  Before you reconnect the battery though, check the two small wires that feed the EFI system.  You might have got lucky and those were switched also, meaning that they are now right.  You don't want to connect your EFI system backward.

image.png

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4 minutes ago, Zed Head said:

Making progress.  The backward battery is one of those Nissan pitfalls that catches many people.  Before you reconnect the battery though, check the two small wires that feed the EFI system.  You might have got lucky and those were switched also, meaning that they are now right.  You don't want to connect your EFI system backward.

image.png

How would I check those? 

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1 hour ago, 280zdude said:

I see can anyone send me a pic of how the smaller cables are connected. Hopefully I bought the car like this there were a couple blown fuses but only for the lights and what not. Hopefully not wires have been shorted in between 

You'll want to use your meter and determine which of the small wires is connected to ground and which is connected to the power supply to the EFI system.

Might be a good time to study a wiring diagram.  Doesn't look like you're one of the lucky ones with a complete car that just needs a couple of small things.  You can't get very far on the 280Z's without building up some good electrical skills.  It will be fun!

 

 

 

Edited by Zed Head

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1 minute ago, Zed Head said:

You'll want to use your meter and determine which of the small wires is connected to ground and which is connected to the power supply to the EFI system.

Might be a good time to study a wiring diagram.  Doesn't look like you're one of the lucky ones with a complete car that just needs a couple of small things.  You can't get very far on the 280Z's without building up some good electrical skills.  It will be fun!

 

 

 

Yup that’s the diagram I’ve been using to check the wires. Let’s see I’m trying to tackle one thing at a time first spark then fuel. Any suggestions on how to check efi if it’s connected properly. The tank is rusted bad sooo I was seeing if the car starts with some starter fluid before getting into that. 

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One way would be to test continuity to pin 73 at the EFI relay.  And I think that the ground wire is redundant, it's also connected to the intake manifold, grounding through the engine block.  While you're there at the battery check the fusible link.  They can look okay but be burned up inside.

The EFI relay is up above the hood release handle in the cabin.  If it's like most 280Z's, it's already been out a few times, might even just be hanging there.

This is the diagram you want to study to find check points.

image.png

 

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By the way, if you disconnect the two EFI connections you should be able to work on the other stuff without it.  It's what people do when they switch  to carbs.

Disconnect here where I circled.  That is EFI power and ground.  Two red wires - thank you Nissan.  Then reconnect your battery, see if the engine still spins (the right way), get your coil power back, shoot some starting fluid, etc.  Let your sub-brain ponder the EFI power situation while you work on that stuff.

image.png

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The length of the wires suggests that they are connected correctly though.  The positive connection is farthest away.  Hope there's no damage.

Your battery is actually what's flipped, which is how you got in to this mess.  Positive typically is under the fender edge.  More Nissan genius.

 

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Right that’s the next step but I tested the coil and that thing was toast. The internal resistance was through the roof! Need to do more studying on that as well 

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4 minutes ago, Zed Head said:

The length of the wires suggests that they are connected correctly though.  The positive connection is farthest away.  Hope there's no damage.

Your battery is actually what's flipped, which is how you got in to this mess.  Positive typically is under the fender edge.  More Nissan genius.

 

And it's a very good idea to orient the battery the way Nissan designed. I had a battery with the positive toward the engine, and it wasn't secured properly. When the battery moved, the positive terminal made contact with the engine. Lots of smoke and burnt wires. With the way Nissan oriented the battery, the positive is less likely to come into contact with ground.

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The car actually came with the original battery flipped from Nissan lol I guess the dealer who installed it messed it up... I’m the second owner of the car 

image.jpg

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The internal resistance of the coil is 11.2 at 200k ohm setting in the multimeter. Primary is .06 on 200 ohm setting.. soo I’m guessing that’s a very bad sign lol

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