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Addition of a Relay to a 240Z Starter System


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FWIW - I've been running a similar relay set-up on my '72 for at least 20 years to solve the same problem described in the article. However, I put the relay inside the car, on the inside of the firewall in the passenger footwell.

Wiring is pretty straightfoward - the original wire going to the solenoid is extended and run into the car to energize the relay then goes to ground. A larger gage wire from the positive battery terminal comes into the car, through the load side of the relay, then to the solenoid terminal.

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It really shouldn't take much current to pull in the solenoid.

My son's Geo Metro had a similar problem. It would only engage the solenoid when the car was hooked to a battery charger or being jumped from a running car. (It seemed to prefer G.M. jump starts, perhaps because they run a little higher voltage.)

Anyway, I fixed the problem by spacing out the starter from the transmission housing with washers. The starter gear was being forced to far past the flywheel, and a couple of extra volts were enough to slam it home hard enough to make the contacts that actually fire the motor.

At first we replaced the starter (twice) but that had no effect. Apparently a PO must have left off a cover plate or something. (Thus the need for spacers)

I only bring it up in this thread because I suspect that the relay may be fixing a symptom, not a systemic problem. There could be some stack-up issue or just a worn or improperly installed solenoid causing the problem.

(or, to be fair... perhaps burnt contacts on the ignition switch.)

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My son and I have had the same starter problem on two cars a 72 240 and a 73, after searching on this form and Hybrid z we have tried cleaning the ground, replacing the starter and ignition switch (which took a long time to source and the local Napa parts store to get in) only to determine that the original parts was just fine.

What we found on both cars is that the ignition switch that the key tumbler turns, the part the wiring attaches too and is held in place with 2 tiny screws, spins ever so slightly to the left if looking from the drivers seat thus not allowing full contact in the start position on the the key tumbler.

I have put in a second switch onto the wiring harness used a flat bladed screw driver and started cars over a hundred times to test this threory and the cars both started ever time.

When I put the wiring back to the switch that is attached to the key tumbler it would not start again just click, so I loosened the little screws rotated the Ignition switch to the right as far as I could, and tightened the screws as tight as I could, reconnected the wiring and the car fired right up.

I wish that was the end of the problem after about a week or so with no starting issues at all the switch rotated back out of position again and the dreaded click returned. What I need to figure out is how to hold the switch in position for a premant fix.

Hope this helps and I think is the actual cause of this annoying problem.


71 240z newly getting full rebuild :love:

72 240z Sons car but gave me the z bug again

73 240z Canadian rust bucket, but good parts car not safe to drive

71 240z my first car written off in 81 :cry:

72 240z had to sell to pay for college in 84 have missed them every since.

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I believe that both Walter and Dave have valid points - eroded switch contacts and loosening of the electrical part of the switch. To that I'll add possible slop developing in the "socket" on the electrical portion of the switch that the mechanical part of the switch engages - this would then affect the degree of engagement of the switch contacts - and possibly promote arcing or otherwise burning the contacts so the problem would get progressively worse...

In my case, I originally had a problem with the start position on the switch - I wired around that with a starter button (that bypassed the "start" switch contacts) and it worked fine . Then, a number of years later, I had a problem with getting the solenoid to engage, even with the starter button that bypassed the ignition switch contacts. Thinking I had a current/power issue (perhaps corroded wires, contacts, etc.) that's when I added the relay. It's now been at least 20 years with no problem.

Since I did all these mods, I have replaced both the mechanical and electrical portions of the ignition switch (as part of installing newer locks on the entire car). The start position on the new switch works so I don't NEED to use my starter button any longer (although, by habit, I always end up pressing the starter button to start the car - 20 year habits die hard). Some day I should perhaps disconnect my relay and restore the wiring to see if it was only a switch problem all along !

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Good food for thought. Thanks for the responses. I get the "click" from time to time. Usually I wait a second or two then try again and the solenoid activates. I'll try cleaning the switch with contact cleaner first along with looking for the "sweet spot".

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It's a great Idea, for any older car like the 240Z. I've yet to do this to mine but it also has'nt been a problem yet.

Sorry for the delay, I'm out of town building a composite decking Deck for a friend. I'll be gone till Monday the 16th.


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