73 240Z Wiring Harness Ground

[bartman]

I'm hoping someone can help me in determining where specifically the wiring harness is attaches to ground in my 73 240Z.  I don't mean a schematic, but where on the car physically the wire harness is connects to ground.  This could be directly to the battery or maybe somewhere the harness is just grounded to the chassis, I'm not sure.  Looking at the schematic it does appear there is a smaller wire connected directly to the battery but I'm not seeing this on the wiring harness.  If this is the case and there is indeed a wire from the wiring harness connected directly to the battery I just need help in locating where in the harness I can find it.

Thanks in advance.

[grannyknot]

Open the hood, just in front and below the battery you will see the wiring harness mounted on the frame rail.

Between the battery and the shock tower there will be a group of 4-5 wires coming out of the harness and attach to the wheel well just above the harness, that is one of the main grounding points, there are others but that is the big one I think.

Chris

[bartman]

4 hours ago, grannyknot said:

Open the hood, just in front and below the battery you will see the wiring harness mounted on the frame rail.

Between the battery and the shock tower there will be a group of 4-5 wires coming out of the harness and attach to the wheel well just above the harness, that is one of the main grounding points, there are others but that is the big one I think.

Chris

Thanks Chris, I found the grounding point you described.  It seems strange to me that it would be so close to the battery and not connect directly to it, which is exactly what I think I will do.

[zKars]

There are two other ground points. Talking 240's here. 280's have EFI related grounds as well.

The second is under the gas tank at the right rear of the chassis just inside the rear valence. It threads into the side of a frame member back there. Gas tank has to come out to get to it.

The third is to the left of the battery on the firewall. There is a 6mm threaded hole. Not the one directly above the battery where the frame attaches, about 2-3 inches left of the top of the battery. It was designed to have a lug from the main '-' battery cable connect there before it goes down to terminate on a starter mounting bolt. This provides the engine block to body ground. Often lost when the old stock cables are replaced with generic ones. If you don't have one, create a 8 or 10 gauge wire to connect that firewall point to some engine block bolt.

Maybe mention the black ring terminal ground connection on the back of the alternator as well? Important for proper voltage reg and alternator reference. 

[bartman]

52 minutes ago, zKars said:

There are two other ground points. Talking 240's here. 280's have EFI related grounds as well.

The second is under the gas tank at the right rear of the chassis just inside the rear valence. It threads into the side of a frame member back there. Gas tank has to come out to get to it.

The third is to the left of the battery on the firewall. There is a 6mm threaded hole. Not the one directly above the battery where the frame attaches, about 2-3 inches left of the top of the battery. It was designed to have a lug from the main '-' battery cable connect there before it goes down to terminate on a starter mounting bolt. This provides the engine block to body ground. Often lost when the old stock cables are replaced with generic ones. If you don't have one, create a 8 or 10 gauge wire to connect that firewall point to some engine block bolt.

Maybe mention the black ring terminal ground connection on the back of the alternator as well? Important for proper voltage reg and alternator reference. 

Thanks for the detailed information, this is very helpful.  Do you think these are all interconnected within the wiring harness?  I think it would probably make sense and maybe this ensures the best ground can always be obtained.

[Captain Obvious]

On my 77 280 there are several different ground connections to the harness, and they do not all connect together inside. Some do, some don't. The ground scheme is the battery cable to the starter bolt and then they use the engine as the distribution center from that point on. There are a couple places where the engine is connected to the body through the harness, but there was no small wire going directly to the battery (exception being for the fuel injection, which you do not have).

So I can't be positive without taking measurements off your harness, but I bet the concept is the same as my 77. I bet there are couple ring lugs that connect to the engine block, and within the harness those connections star out to things like the turn signals, marker lights, coil, etc. as well as connect to the body. But there may be more than one star point. I think my 77 had two of them... One on the pass side area, and one on the driver's side area.

[240260280]

@zKars

 

I'm restoring a friend's 1973 but I forget where the ground wire near the gas tank comes off the harness. Do you recall?  Here are rear gnd pics for a 71 resto I did but I can't figure where it came out of the harness.

 

Here is the gas tank area gnd.

 

 

Here is the one near the antenna:

 

 

[zKars]

The ground is in the fuel sender/fuel pump harness that goes through the hatch floor just beside the right rear tail light. It attaches to bolt that goes into the side of the frame rail above the tank. Totally inaccessible without removing the tank.  If you think that lug is corroded, you are right. Just splice into the black wire above where it goes down below the hatch floor and make a new ground connection near the tail light. Sheet metal screw about 3 inches long should go right into the gas tank if you aim it right

[240260280]

Thanks Jim,

 

The 73 harness has the two fuel sender wires and a green and black wire coming out of the same part.  I thought both the green and black were for an optional fuel pump... it the black the harness ground I am looking for?

 

1971 fuel sender and harness connection

 

 

 

Here is other stuff I documented on the 71:

 

Broken Rear gnd wire from harness?

 

 

Patching and extending a new connector

 

Extended and fastened.

 

 

[w3wilkes]

12 hours ago, 240260280 said:

The 73 harness has the two fuel sender wires and a green and black wire coming out of the same part.  I thought both the green and black were for an optional fuel pump... it the black the harness ground I am looking for?

 

1971 fuel sender and harness connection

The green and black at the tank are for a optional fuel pump. The green wire doesn't have power by default. There is a connector in the harness up at the front of the console that is connected to nothing and taped with blue tape in the harness. The connector has 2 green wires. You can just jumper this connector and it sends power to the green wire at the tank. It is on the key and powered with the key in the On position. The black wire is the Neg (ground) for the pump. If you do a electric fuel pump you should put an inertia switch in the loop to jumper the connector so power to the pump will be cut in a crash.

The dealer did put in an electric pump in my 73 after my complaining about vapor locking. Don't know about how the wiring was done up at the console, but there were a couple more relay type brass enclosures put on the body side of the passenger footwell kick panel. On my 71 I just jumpered the connector with an inertia switch in the loop.

Edited March 12, 2019 by w3wilkes