12 Volt switch source

[Pomorza]

Hey guys,

I'm planning on installing two new gauges in the Z but am having a hard time finding a 12 volt switched (i.e car has to be on) source. Any ideas?

Thanks

Jan

[EScanlon]

Radio or A/C power leads Blue/Red in the earlier cars.

As long as there haven't been any perversions done to the car, you could just tap into the wiring. However, if the instruments you're adding need a pulse free power source, you may want to avoid the A/C one.

E

[EScanlon]

Radio or A/C power leads Blue/Red in the earlier cars.

As long as there haven't been any perversions done to the car, you could just tap into the wiring. However, if the instruments you're adding need a pulse free power source, you may want to avoid the A/C one.

E

[Pomorza]

E.

I searched every free wire in the radio area and there's not a single one that is switched. There were two that were constant 12 volt sources but none that were switched. Any ideas? Anyone?

[EScanlon]

The wire you're looking for may not be loose, it may be in use. The Radio power wire will almost definitely be plugged in to the back of the radio. The AC line may also be connected if the AC is installed.

However, both of those wires will allow you to splice into them, and as long as your instrument power needs aren't excessive you won't have any problems. The problem lies in ensuring that. Look at the documentation that came with the gauge and see what the power requirements are, add those to the Radio's requirements and that way you will know if you are exceeding the fuse for that circuit. Don't forget to leave a margin for safety (surges).

Most new instruments will only require a few amps if not barely an amp, but it depends on the instrument.

Another possibility is to wire directly to the ignition switch, but here you're tapping at one of the main circuits which is why you hear of PO's having messed up or cobbled the wiring, so be careful. At the ignition switch I'd look for the wire leading to the Accessory Relay, it doesn't get power until the switch allows it.

I am more familiar with the 240's, so I can only suggest generalities for the 280. Have you checked the wiring schematic and seen what is showing and where?

FWIW

E

[EScanlon]

Another thought, PM SBlake01, he's very knowledgeable on the 280's and it would not surprise me if he didn't know of a wire right off the top of his head.

E

[Jeff G 78]

Not sure if it's on the '76, but on the '78, there is an unused blade connector on the RH kick panel above the fusebox. I went through the same search and someone on the forum pointed me to that source.

[EScanlon]

Not sure if it's on the '76, but on the '78, there is an unused blade connector on the RH kick panel above the fusebox. I went through the same search and someone on the forum pointed me to that source.

Not positive, but would not be surprised to find out it was Stephen who pointed it out. His knowledge of the 280's is close to encyclopaedic.

For the record, he is also a whiz with Air Conditioning.

E

[Pomorza]

Hey guys,

So I found a 12 volt source but do have a question. What exactly makes this a "switched" source. Is it the key itself or is there a relay someplace. If the ignition was going bad (the key that is) could this cause fluctuations in the voltage output?

Thanks

Jan

[EScanlon]

"Switched" refers to it being turned on / off by the ignition switch, whether directly or by a relay is secondary.

(Conversely, "non-switched" means CONTINUOUS power, i.e. it's ON as long as the battery is connected to the car's harness.)

Typically, it's the current load to be controlled that will determine if it should be run through a relay circuit or if it can be run through the ignition switch. Higher CURRENT circuits are best through a relay. (So are High Voltage circuits, but we're talking about a 12v Car.)

The 240 Z's headlight circuit is a good example of an item that is NOT on a "switched" circuit (controlled by the ignition switch) that is safer and better through a Relay circuit instead of part of the car's wiring.

Other examples of Non-Switched are Hazard Lights and Brake Lights, the Cigar Lighter and the Dome lamp.

The Starter is another good example, but now it is an item that IS "switched" AND on a relay, although it's called a starter solenoid.

Here you have the rest of the car's circuits which, without the ignition switch being toggled to the ON position, would not be functional; i.e. the radio, turn-signals, gauges, and the distributor/coil etc.

Now, you can check to see if it's a switched source simply by putting a light on it and seeing if you have to have the key on or not for the light to turn on.

Key OFF and NO light / Key ON and YES light = Switched

Key OFF and YES light / Key ON and YES light. = Non-Switched.

If your ignition switch is starting to go bad, and you now have intermittent electrical contact at it's connections, don't hesitate to replace it. An intermittent electrical source can quickly fry any component attached to it, regardless of whether it's on a direct or relay circuit. Simplistically, not so much because of a voltage drop, but due to the changes in the current supplied. You're literally turning it on and off repeatedly.

I gave you more of an explanation so you can determine by what you are connecting, whether you should use relays or not. (and also future readers of this post)

HTH

E