75 280Z - Starter Motor intermittently clicks when restarting after car has been driven for several miles/in town driving

[Zed Head]

1975 seems to have some odd features.  The wiring diagram shows an "interlock relay".  It exists for both Manual and Automatic.  Could be involved.  I don't know how it works.  I think that the 74 260Z's have it also.  @SteveJ knows about, I think.  The diagram might be a holdover from the 260Z though.  The 75 FSM does not describe it.

Either way, your problem seems tailor-made for a test light with alligator clips.  Set it up on the circuit you're testing, turn the key, see what the light does.  If you get the click but the light stays on the problem is downstream.  If the light goes off it's upstream.  

 

Edited June 6, 2023 by Zed Head

[Zed Head]

I downloaded the wiring diagram years ago from 240260280's AtlanticZ site years ago.  It is excellent although it is black and white.

http://www.atlanticz.ca/zclub/techtips/electrical.htm

[SteveJ]

38 minutes ago, Zed Head said:

1975 seems to have some odd features.  The wiring diagram shows an "interlock relay".  It exists for both Manual and Automatic.  Could be involved.  I don't know how it works.  I think that the 74 260Z's have it also.  @SteveJ knows about, I think.  The diagram might be a holdover from the 260Z though.  The 75 FSM does not describe it.

Either way, your problem seems tailor-made for a test light with alligator clips.  Set it up on the circuit you're testing, turn the key, see what the light does.  If you get the click but the light stays on the problem is downstream.  If the light goes off it's upstream.  

 

I've never had the opportunity to tear into the wiring of a 75, but I strongly suspect that the interlock relay has been completely disabled. 

Ford developed the seatbelt interlock relay and presented to the NHTSA in the early 70s. The bureaucrats thought that it was the perfect solution for getting people to wear their seatbelts, so they quickly added it to the regulations for the 74 MY cars. This meant all of the other automakers selling cars in the US had to come up with their own interlock schemes and QUICK. Many of the implementations left a lot to be desired. I remember my older brother figuring out how to disable it in our family's 74 Impala.

Faced with a litany of complaints along the lines of cars not starting unless the bag of groceries was buckled safely for the trip home, the NHTSA quickly unwound the requirements. Most automakers were even quicker about removing these bastard implementations. However, documentation is usually the last thing the engineering team wants to address, and I'm betting all of the proofs were already completed for the service manuals for the already delayed debut of the 280Z before they got yanked.

If the interlock relay did ever exist in a production 75, I would expect it would have the emergency bypass switch like what the 260Z had.

More useless trivia: The switch was moved between the early and late 260Zs. On the early (first 12 months) car, the switch is on the right fender, near the battery. On the late (last few months) car, the switch is mounted on the firewall.

[HusseinHolland]

Video of the click/ammeter draw. This happened when I was sitting in queue for the pharmacy to pickup my Mum's prescription 😞

YT Video

So, I added the starter relay when I got home. I'll see if that resolves the symptom. I didn't eliminate the fusible links yet, I want to do one thing at a time

 

added riv-nuts to the top to secure the fuse panel that will replace the fusible links, and supply current for the headlamp relays, etc., moving forward

bridge wires routed 

@Zed Head- thank you for the wiring diagram link

I don't think there is an interlock relay on the car

 

Edited June 7, 2023 by HusseinHolland

[Captain Obvious]

I like the video. I can feel the frustration through the screen. 

So I'm not sure if the click on the video is the starter solenoid or not. Can't tell from my seat.

And as for the ammeter... I see the draw. If the gauge numbers are correct (and I have unknown to low confidence in the accuracy of the numbers on the gauge face) it appears that the car is drawing 20A or so when you turn the key to START. Question is... Is that a reasonable draw even WITHOUT the starter solenoid engaged? Does the ballast defeat and other associated functions come to anywhere near that when in START? I think I could be convinced that all the other ancillary functions can come close to that even without the starter solenoid.

Let us know how the starter solenoid works out.

I saw in one pic that your car is a manual trans. Did it come from the factory that way, or was it converted? Also, is your car a California spec? Do you know?

[Captain Obvious]

10 hours ago, HusseinHolland said:

Thanks for the schematic - I was wondering if the starter solenoid trigger came through a fusible link The green one does feel pretty warm to the touch.

Oh, and... Yes, the link that feeds the ignition switch is the green one.

And that schematic was originally made for 77/78. The concept still works fine, but the wire colors are a little different for 75 and 76. I'm sure you've already figured that out.

[Zed Head]

Interesting that the draw doesn't affect the other gauges, not even a needle quiver.  But it does affect that horn noise. Not sure what that is, is it the seat belt warning buzzer?

I have to say/ask - why are you avoiding the simple electrical diagnostic methods?  It's a very straightforward circuit with a simple solenoid at the end.  Low current, one device.  I almost replaced my starter when the spade terminal lost contact but then I pulled back to the basics and figured out what was happening. 

Another time on a Ford Escort I was halfway down to the starter when my brain told me the symptoms didn't match what I was trying to fix.  It was a loose battery terminal (not your case since the gauges don't move).  

Notice on the wiring diagram that there are other functions on that Starter wire from the ignition switch.  You could check those to find the break.

[HusseinHolland]

7 hours ago, Zed Head said:

Interesting that the draw doesn't affect the other gauges, not even a needle quiver.  But it does affect that horn noise. Not sure what that is, is it the seat belt warning buzzer?

I have to say/ask - why are you avoiding the simple electrical diagnostic methods?  It's a very straightforward circuit with a simple solenoid at the end.  Low current, one device.  I almost replaced my starter when the spade terminal lost contact but then I pulled back to the basics and figured out what was happening. 

Another time on a Ford Escort I was halfway down to the starter when my brain told me the symptoms didn't match what I was trying to fix.  It was a loose battery terminal (not your case since the gauges don't move).  

Notice on the wiring diagram that there are other functions on that Starter wire from the ignition switch.  You could check those to find the break.

The buzzer comes on with the key in the ignition, door open it will stay on, otherwise it goes off as soon as the engine starts.

Partly because I hate those whole car diagrams that have no color coding. I can't read them easily & tend to cross circuits in my head.  The best ones I've ever dealt with are Volvo. They show every individual circuit, but include ANY associated junctions that overlap, so they is no question of what you are looking at. They also show current flow in each case.

example:

Beyond that, I am totally unfamiliar with the Datsun wiring conventions & I really don't want to spend hours on visualizing the overall path of the given circuit in my head; I have to do that when fault tracing. Given that the issue is in the starter circuit I'd rather just do what I can with things like the starter relay, which if the issue with load on the factory circuit, will now be completely negated. I'm going to do a drivetrain conversion on this, so I also don't want to go too nuts with the stock engine management either. That's another reason I'm adding the additional power management in the bay.

[HusseinHolland]

10 hours ago, Captain Obvious said:

I like the video. I can feel the frustration through the screen. 

So I'm not sure if the click on the video is the starter solenoid or not. Can't tell from my seat.

And as for the ammeter... I see the draw. If the gauge numbers are correct (and I have unknown to low confidence in the accuracy of the numbers on the gauge face) it appears that the car is drawing 20A or so when you turn the key to START. Question is... Is that a reasonable draw even WITHOUT the starter solenoid engaged? Does the ballast defeat and other associated functions come to anywhere near that when in START? I think I could be convinced that all the other ancillary functions can come close to that even without the starter solenoid.

Let us know how the starter solenoid works out.

I saw in one pic that your car is a manual trans. Did it come from the factory that way, or was it converted? Also, is your car a California spec? Do you know?

 

Yeah - I edited out the F U C K  at the end of the clip 😆 maybe the click is just the various relays that are powered on start. Perhaps that draw is reasonable. When it starts normally, the draw is so brief it's hard to gauge whether it's pulling that much. 

I'll update with results after I've driven it awhile in warmed up stop & start conditions.

This is an original manual trans, 4 speed California spec car - has the cat, floor temp warning circuit, etc., I bought it from the original owner in California, and everything on the car is pretty much original (and worn out). Besides the dealer-added AC, and the more recent EFI harness hack, I haven't found any evidence of ****ery on the car

Edited June 7, 2023 by HusseinHolland

[Captain Obvious]

Well there's lots of diagnosis that could be done to figure out what the real underlying issue is, but at this point, if a starter relay makes it go away, then it sounds like that's going to be good enough for now.

There is some extra stuff on the CA spec cars that gets engaged when the key is in the START position, but I don't know how much current it would draw. With a quick look at the wiring diagram, it looks like it would be just a couple more "lamp test" lights in the HVAC vent panel, but in your video it looks like that panel (and it's associated light bulbs) is not installed.

Anyway, still hoping that the starter relay takes care of it.

if you're looking for something simple to use to test some of the theories (and get you out of a jam like when you're sitting in the que at the store)? Run two wires from your starter into the interior. Use those two wires to short to the solenoid directly like you were doing manually out in the engine compartment. Put a switch on it in the interior if you're feeling fancy (push button start like the new cars  ), or just connect the two wires together if you need to.

[HusseinHolland]

Another question - mounted on the relay bracket is a rectangular unit (#4) described as a "shunt unit" I'm not seeing what the purpose of this unit is. Any input on that?

 

[SteveJ]

13 minutes ago, HusseinHolland said:

Another question - mounted on the relay bracket is a rectangular unit (#4) described as a "shunt unit" I'm not seeing what the purpose of this unit is. Any input on that?

 

The shunt is for the Ammeter.