13 hours ago, zclocks said:

Dave, 

A couple more photos of what My 75  looks like. No Ground wire attached to the terminal block. Mine is bone stock

Ron

Ok now I am bugged, can you pls take a look at where that large white spade connector goes to? Not usre if that is a purple or black, black I assume.

Another mystery, I do NOT have that ground connection shown attached to the nut under the term block. I have a place for it (the hole on the term block mount) but it is unused.

I checked the FSM engine harness #2 detail B did not show those, but the FSM I am looking at was for 75/76

Edited December 31, 20195 yr by Dave WM

looked at the PDF online FSM for 75 found this, def different from my 75.

ah now this is from a 76, so my 75 must have gotten the new harnes

BE.pdf

Dave, 

The black wire, spade connector , goes to ground. The attachment of the ground is under the AFM plate, but could go anywhere for ground. 

Again mine is a 75 CA model so it might be different. Couldn't open the BE.pdf. Also is the pdf , the one on line from the OEM FSM? I have a hard copy manual and don't see it if you can give me a page # I can look for it. 

Ron

 

OK,  I found the page in the FSM , BE 88. It says the spade connector goes to the AF sensor. If you look at the schematic for the 75 280 it shows that the spade connector is ground and goes to the AFM. 

Question : is you take the terminal block cover off is the black wire connected to the green wire?

On 12/28/2019 at 2:32 PM, Dave WM said:

here is a pic of my setup

 

I'd like to see where that black wire is connected also.  Looks like somebody in the past either made a bad guess or used some bad logic.  Wouldn't be surprised if it was just connected to the cover screw.  Ground to ground.

Dave , 

Taking a second look at the new lug attached to ground looks like this was a new addition. Can you provide a photo with the cover off the 

terminal block? Also, the green and red wires come from your distributor. If either is grounded then it would be shorting out the spark timing.

 

it was right on top of the green lead under the block. already removed and discarded (when I was taking it off the poorly crimped on eyelet under the term cover fell off, def not OE).

As far as grounding the green, it worked, I presume the signal wires are electrically isolated, so if only one lead was grounded it still works. I did note that with the ign on engine off, intermittent contact with the ground from the green signal wire would fire the spark. mentioned that a while back ZH speculated that it was just a slight change in the electrical potential from the grounding of the one lead. OR it was making no contact do to the poor crimp, but I doubt that. I have been driving it for years that way, and I am pretty sure when I started down this path of trying to figure out the issue, I did a resistance check of the green term to ground and it was a very low resistance reading that you would expect with a wire to ground connection.

 

Pretty sure I verified the isolation by checking for resistance from the dizzy pick up coil to ground (completely open) same with the term block wires, no ground path on either red or green. That is with the non OE wire removed.

I have no idea what the logic was from the PO on this hookup I am with ZH either a bad guess for just bad logic. Only think I can think may have been an attempt to ground the mount plate with the intent to connect to a body bolt near the term connector. Not needed of course since the correct OE ground wire was in place and attached in such a way as to ground it thru the chassis using the mount screw.

Of course the idea of using the green term block as a ground makes no since at all but, that is the only thing I can come up with. its so obvious that no extra wire belongs there, even just looking at the rubber plug on the side of the tern block you can see cut outs for wires, and you can tell its not cut to allow 3 wires out of the block.

Prob should have a thread for "Mystery Mods by PO's"

:)

 

 

Edited December 31, 20195 yr by Dave WM

Hi Dave, here's what wiring my May '75 build Z has:

 

yep that's it. I will check but I think mine was a Apr build.

I had just removed my AFM a few days ago (to facilitate other maintenance) and there weren't any rubber grommets installed on the mounting bracket screws.  According to the diagram in the Car Parts Manual, there should be 6 total grommets (3 for the screws that screw in a downward direction, and another 3 that are for the screws that screw in from the bottom of the bracket upward).  My car is a 78, and from the diagram it looks like all Zs had this configuration from 02/76 through the end of the 78s.

The rubber grommet part numbers are:

22683-N4201 (3)

22684-N4201 (3)

And, of course, these parts are NLA for purchase (according to courtesy nissan).

Would one of you be willing to post a photo of one or both of these grommets (removed from the bracket) showing enough detail that would allow me find a suitable substitute grommet(s)?

BTW, there was a ground wire attached to 2 of the screws on the bracket, but with the grommets absent, I don't see how it served any useful purpose.

 

 

Dave, I haven't looked at the design of the ignition modules to see if they reference either side to chassis ground. My assumption is that neither side would be tied to hard to ground in the module. That assumption is based on the twisted-pair nature if the pickup wiring. They are trying to reduce the loop area with the twisted pair and it would completely defeat that purpose if they would tie one side to ground in multiple locations.

My assumption without any reverse engineering is that the pickup inputs are not galvanically isolated (with a transformer or something), but they may feed some sort of floating input differential amp at the input stage of the module. If that's the case, tying one side to ground might not cause it to malfunction, but it certainly isn't necessary or desired.