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1975 280Z
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Discussion Starter · #1 ·
I have a recently acquired 75 280z that is having some starting issues. If the car is able to turn over it will start reliably however, that is a coin toss as to if it will turn over. When keying on the car there is an audible click under the passenger dash on all key positions after ACC. I also pulled that starter motor to test it outside of the engine and it functioned fine when bypassing the other components. Fusable links I assume would still be fine since the car can still start albeit sporadically. Any one have any guesses as to what the issue may be?
 

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What is the battery voltage, and how old is the battery?
What is the voltage to ground at the terminal for the solenoid?

If the voltage is low, the solenoid might not engage. If the voltage is good, but the solenoid engagement is inconsistent, you should consider getting a replacement solenoid or rebuilt starter.
 

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1983 280ZX Turbo
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If the solenoid is what's clicking, that normally means low battery.

Also, the starter portion of my 1983 ZX recently wore out and I had to replace the ignition switch.
 

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1975 280Z
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Discussion Starter · #4 ·
Battery reads 12.9 volts with a multimeter but that was under no load. Will have to check the voltage to the ground of the solenoid. Would that just be done by connecting a lead to the empty post of the solenoid?
I was assuming the clicking under the dash was the starter relay engaging but it may be worth it to pull it out and test that out.
 

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You test the voltage at the solenoid by placing the lead where the yellow wire goes on the solenoid. There isn't much exposed metal, but there should be enough to place a meter positive probe. The negative probe should be on battery negative or a chassis ground.
Voltage will drop while cranking, but if your battery is in good condition, it should not drop below 10 volts.

The only possible relay in the starter circuit would be the mislabeled "SEAT BELT RELAY". It's actually a relay controlled by the inhibitor switch for the automatic transmission. You would only have that relay if the car started life as an automatic. A bad inhibitor switch could prevent the solenoid from receiving power. Again, that is only if the car has an automatic transmission.
 

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1975 280Z
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Discussion Starter · #6 ·
I will test out the solenoid when I get back Sunday evening. ZCar depot sells what they call a starter relay but upon further investigation I believe this is the ignition relay. I don't believe the car started life as a transmission, but I do know the 5 speed in there now is not the original.
 

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Here's what happened to me recently on my'78. It ran fine in the morning, then in the afternoon, no crank. Battery voltage normal until I tried to crank, then battery voltage dropped to zero. Bad battery? Nope. It was a corroded battery terminal. When I cleaned it up it started and ran perfectly.
 

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Try a remote start switch, where you jump between the battery positive and the solenoid. Or, when it is in a mood just take a screwdriver and bridge the positive post on the starter and the spade on the solenoid (with the wire disconnected). If it cranks consistently then, put a relay in to supply voltage to the solenoid.

The problem is that the load to activate the solenoid is carried through the ignition switch, and it is a bit too much load for it. Over time the contacts in the switch arc, the connectors on the back of the switch melt and burn. You end up with a cycle of increasing resistance and heat. I always like to add a relay near the started to power the solenoid. Then the switch only needs to carry enough amperage to close the relay, and no more melting connectors!

I will do the same with the headlights and horns.
 

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1975 280Z
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Discussion Starter · #9 ·
Finally found some time to get back to the car, voltage from battery to the spade terminal on the starter measured at 11.5 Volts. Car was also starting fine today so I'll have to try the test again when it is being temperamental to further diagnose it.

Would the relay just be wired from battery + to the spade of the solenoid and use the original starter wire to activate the relay or is there a better way of implementing a relay into the circuit?
 
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