Starter motor question

[Dcreech0]

Hello all. I really hope I can get some positive help here

i recently purchased a 1971 240z that has an l28 swap that had set in the desert a couple years not running. So long story short, the previous owner had done some really “hackery” of a job to the wiring in the whole car. 
I have spent the past week or so getting the car ready to crank and start for the first time. I finally got the car to start and of course idled a little rough. But my concern is that when the engine stumbles and is about to die the starter solenoid kicks back on by itself without me touching the ignition. 
what could be the cause of this? I have installed a new starter and a new ignition switch. 

[cgsheen1]

Automatic transmission? (ever?)

The reason I ask is that the start "signal" generally goes straight from the ignition switch to the starter solenoid - in Datsun Z cars it's a Black/Yellow always. But in an auto car the B/Y goes through an inhibitor switch first. So if the car is/was auto and that wiring and/or switch is screwed up? 

The other thing that comes to mind is in some years the B/Y was also run to the ballast resistor as a by-pass to give full battery voltage to the coil at start. Do you have a B/Y at/near the ballast resistor (or where it would have been). Otherwise the start circuit is one of the most simple circuits in the car - just ignition switch to the starter solenoid...

Easiest fix would be to just run a new solenoid wire from the ignition switch to the starter. That would eliminate all other possible sources of voltage to the solenoid.

 

[Mark Maras]

I can't think of a direct reason for the starter solenoid to activate when the engine stumbles but If you are trying to keep it running by pumping the throttle or pushing in the clutch or something similar, you may be hitting a bare wire under the dash, by the pedals, due to the PO's hack wiring job. Something, somewhere must be completing the solenoid circuit.

[Dcreech0]

39 minutes ago, cgsheen1 said:

Automatic transmission? (ever?)

The reason I ask is that the start "signal" generally goes straight from the ignition switch to the starter solenoid - in Datsun Z cars it's a Black/Yellow always. But in an auto car the B/Y goes through an inhibitor switch first. So if the car is/was auto and that wiring and/or switch is screwed up? 

The other thing that comes to mind is in some years the B/Y was also run to the ballast resistor as a by-pass to give full battery voltage to the coil at start. Do you have a B/Y at/near the ballast resistor (or where it would have been). Otherwise the start circuit is one of the most simple circuits in the car - just ignition switch to the starter solenoid...

Easiest fix would be to just run a new solenoid wire from the ignition switch to the starter. That would eliminate all other possible sources of voltage to the solenoid.

 

Hey! Thanks for the replies. The car always was and still is a manual car. 
mom the B/Y wire theory though.... wire have been cut and moved by the ballast resistor also so I though it would look. So right next the the resistor in the loom there is a B/Y wire that goes back under the brake master cylinder. It’s a female spade connection but not connected to anything at all. 
I am going to try and attach pictures. Also just throwing in a starter picture for reference 

[Zed Head]

2 hours ago, Dcreech0 said:

the starter solenoid kicks back on by itself

 

2 hours ago, Dcreech0 said:

1971 240z that has an l28 swap

So, does the engine never die because it automatically restarts?

Describe more about the L28.  Is it carb'ed or EFI?  Are you using  mechanical fuel pump or electric?  Can't really diagnose a non-stock setup without knowing what you're using.  The Start circuit should only be active when the key is at Start.

Why did you replace the ignition switch?  For this problem or some other reason?

[Dcreech0]

2 minutes ago, Zed Head said:

 

So, does the engine never die because it automatically restarts?

Describe more about the L28.  Is it carb'ed or EFI?  Are you using  mechanical fuel pump or electric?  Can't really diagnose a non-stock setup without knowing what you're using.  The Start circuit should only be active when the key is at Start.

Why did you replace the ignition switch?  For this problem or some other reason?

It sounds like the starter solenoid never disengages even after the engine turns over. Or at least I assume because it will stumble and the starter will just continue to crank. All while I stand out of the engine bay touching nothing. Obviously turning the key back to the off position stops it. 
The motor is still running am the dual SU carbs, but I have changed over to an electric fuel pump and deleted the mechanical fuel pump. 
I replace the ignition with one from MSA because I bought the car with “lost keys” (already pulled the passenger lock and got the code to call a locksmith but just wanted a new ignition switch to rule that out). 

[Zed Head]

Why did you replace the starter?  Trying to figure out if the new parts caused the problem.

It might be mechanical.  Connect a voltmeter or test light to the starter solenoid and see if it has power after you let the key go back to Run.  If it only lights up on Start then it's not an electrical problem.  If the light or meter show power while the engine is running then it's an electrical problem.

[Dcreech0]

2 minutes ago, Zed Head said:

Why did you replace the starter?  Trying to figure out if the new parts caused the problem.

It might be mechanical.  Connect a voltmeter or test light to the starter solenoid and see if it has power after you let the key go back to Run.  If it only lights up on Start then it's not an electrical problem.  If the light or meter show power while the engine is running then it's an electrical problem.

I replace the starter just out of sheer ocd. The old one looked very old and made some odd noises and cranked very slow. 
I just tried to go through and replace a lot of wear and tear items when I got it. Plugs/wires/coil/oil/fuel filter/fuel pump/distributor cap etc. 

[Dcreech0]

Worth mentioning also I am upgrading to the zx alternator but havnt completed that wiring yet. That wouldn’t be in part of the ignition circuit would it?

[Zed Head]

10 minutes ago, Zed Head said:

Connect a voltmeter or test light to the starter solenoid and see if it has power after you let the key go back to Run.

This will answer the question about if it's an electrical problem.  There's just one small wire to the solenoid and it only does one single thing.

Starters do bind up sometimes.  The drive gear gets stuck in the ring gear.

[siteunseen]

That's what I thought, could be a bad starter.

[Dcreech0]

I think maybe I figured it out. Possibly.... in my attached picture diagram, the wire that shown going from the oil pressure switch to the starter solenoid.... where should this be attached to? It’s lists it should be + when starting? I had run this to the starter spade connection along with the B/Y wire