Electrical Gremlins: Ignition and Temp Gauge

[jfa.series1]

I have two problems, am presuming right now they are not connected.

1. Ignition switch - the engine will not stop running when I turn the ignition switch off. Some background: the car just had the rebuilt engine installed and when we went to fire it up, the ignition switch worked initially to start the engine, then gave up on the starter circuit after a couple of cycles. I used a jumper to the starter solenoid for subsequent starts. We also noticed the engine would not stop when the switch was turned off. I pulled the B/W wire on the coil to kill the engine. My diagnosis: worn out ignition switch. Got a new one and installed it today and the starter circuit works great, however the engine still will not stop when the switch is turned off. Resorting to the B/W wire solution.

2. Temp gauge - the gauge initially worked when we fired up the engine and for several run cycles after. I brought the car home and started it the next day - the temp gauge did not work, same result today. As part of the rebuild, it has a new temp sensor in the thermostat housing. The wire to the sensor is in good shape and it has a tight connection.

Details on the car are in my signature.

Thanks for any help.

Jim

[Arne]

Any changes to the alternator? The ignition problem sounds like a bad diode.

[LeonV]

For the temp gauge, pull off the connector to the thermal transmitter and clean off the corrosion. Mine worked intermittently until I cleaned off the male connector coming off the thermostat.

[EScanlon]

Did you "upgrade" the alternator to the internally regulated alternator? If so you need the alternator adapter installed. The stock external regulator AND the internal regulator are providing a dual path for the juice to get to the coil, that's why you're having to kill the power to the coil.

Temp gauge... was it installed with teflon tape on the threads? If so, remove it and clean that stuff off. It's insulating the gauge's sensor from completing it's circuit.

FWIW

E

[SteveJ]

Darn, I thought I responded to this last night. If Enrique is correct that you have an internally regulated alternator paired with an external voltage regulator, then you should be able to detect that with a voltmeter at the battery with the car running. Unfortunately it's easy to detect because you'll have an overvoltage situation that can do VERY bad things to your electrical system.

Also note that jumpering out the voltage regulator won't necessarily resolve the issue with the car not shutting off. You will need a diode in the alternator circuit when you use an internally regulated alternator to prevent it from feeding back through the ignition.

For the temperature gauge, the sensor itself is the load in the circuit. You should be able to read voltage between the sensor wire and ground when wire is unplugged. It's good to verify that you have a signal first.

[jfa.series1]

Thanks for the feedback, looks like you guys have identifed one or both problems.

Yes, I have a 280ZX alternator upgrade. I initially had the regulator replacement adapter in place but was seeing no charge on the ammeter and discharge for lights, turn signal, etc. I presumed the adapter was bad so I pulled it and installed the original regulator, getting a modest charge showing and small discharge for lights, etc. Looks like I must go back to the regulator replacement adapter. Not being too good at auto electrics, how do I determine if I am getting a charge with the new set-up?

On the temp sensor, I may have used teflon tape or other thread sealant. I will pull it and give the lock nut threads a good cleaning.

Steve - if I understand you correctly, I should be able to measure voltage between the sensor terminal and ground? Can I test this at any time? Engine hot or cold, running or not?

Thanks,

Jim

[SteveJ]

Thanks for the feedback, looks like you guys have identifed one or both problems.

Yes, I have a 280ZX alternator upgrade. I initially had the regulator replacement adapter in place but was seeing no charge on the ammeter and discharge for lights, turn signal, etc. I presumed the adapter was bad so I pulled it and installed the original regulator, getting a modest charge showing and small discharge for lights, etc. Looks like I must go back to the regulator replacement adapter. Not being too good at auto electrics, how do I determine if I am getting a charge with the new set-up?

On the temp sensor, I may have used teflon tape or other thread sealant. I will pull it and give the lock nut threads a good cleaning.

Steve - if I understand you correctly, I should be able to measure voltage between the sensor terminal and ground? Can I test this at any time? Engine hot or cold, running or not?

Thanks,

Jim

Jim,

You can always download a copy of the 78 280Z FSM or any 280ZX FSM from XenonS30 or XenonS130. From there, you can see the alternator diagnostics. Another way to check is to take a voltage measurement at the battery with the car off. It should be between 12 & 13 volts with a good battery. Have a buddy start the car and hold the throttle to between 2000 & 2500 RPM. Take another voltage reading. It should be between 14 & 15 volts. To be perfectly clear, jumper out the external regulator BEFORE doing this test. This test is just off the top of my head, but the FSM will give you solid diagnostics.

As for the voltage for the temperature sensor, detach the wire from the sensor, and measure from the wire to ground. The key should be in the ON/RUN position. The engine does not have to be running, but it won't hurt if it is running. The key position is what is important. You have to have voltage going through the gauge. By the way, has the oil pressure gauge been working? Those gauges have a common 12VDC+ coming in.

[jfa.series1]

Success on both issues (well, almost perfect)!

Removing the old voltage regulator and re-installing the adapter cured the ignition problem. Also, removing the temperature sensor and wire brushing the threads on the retaining nut seems to have cured the temperature gauge problem.

Right now there is one remaining question: I am seeing about 1 needle width of discharge on the ammeter with the engine running. I am not seeing any movement on the needle when I increase revs. I have a new battery and it shows fully charged on my maintainer (charging light is off).

Steve - I will try the voltage test you recommended. Should I remove the regulator adapter for this test? And yes, the oil pressure gauge works.

Thanks,

Jim

[Jetaway]

Success on both issues (well, almost perfect)!

Right now there is one remaining question: I am seeing about 1 needle width of discharge on the ammeter with the engine running. I am not seeing any movement on the needle when I increase revs. I have a new battery and it shows fully charged on my maintainer (charging light is off).

Thanks,

Jim

Total stab: Could the maintainer be keeping the battery at a higher voltage than the car's charging system is putting out? Would that produce the drain that he sees on the ammeter? If so, is it nothing to worry about as the alternator will start charging once the battery voltage drops sufficiently or does the poor guy have some more poking around to do?

Chris

[SteveJ]

Jim, no, you shouldn't remove the adapter. While the voltage measurement is a quick & dirty check, it doesn't replace the diagnostics in the FSM. Those diagnostics will help you pinpoint the problem.

Chris, if the alternator is putting out less than 13.2 volts with the engine at speed, there is a problem with the wiring or with the alternator. Again, the FSM diagnostics will pinpoint the problem.

Oh, and by the way, the FSM for a 78 280Z or for a 280ZX will have diagnostics to help pinpoint the problem.

[jfa.series1]

Thanks for the additional feedback.

Jim

[EScanlon]

The BASIC problem is that you are using a later year alternator in an earlier year wiring circuit.

You can go ahead and use all sorts of fancy instruments, data, interpolation of results, statistical analysis and all the fancy terminology you want, but you are still going at this bass ackwards.

The reason you're not showing a charge through the Ammeter is basic. By removing the original Voltage Regulator, which included the Ammeter in it's circuitry, and using an internally regulated Alternator (with the Alternator Adapter) that does NOT use it, you've eliminated the Ammeter from the circuit.

2¢

E