Wiring Question, Switched Hot @ Fuse Panel Options

[andys]

I need to run a some relays for my V8 conversion, and need a switched +12 volt source. I'd like to tap into a source off the fuse panel. My question is which fuses are 'on' when ignition is on (switched)? I'm pretty sure fuse #8 is switched, but which others are switched? I'd like to use #8 since it's for fog lights (which I don't have), but I believe it's constant +12 volts (since a relay switches them on). BTW, the wiring is incomplete so I can't simply power up the system and turn the ignition switch to read switched sources.
Thanks,
Andys

[zonedoubt]

914 Fuses

[andys]

914 Fuses

zonedoubt,

Thanks for the fuse chart, but I already have that. What I need to know which ones are switched on (hot) only when ignition key is turned on.

Andys

[andys]

Anyone?

Andys

[zonedoubt]

The circuit diagram is your friend. Haynes has one, and they're also on the popular sites.

Fuse 9 connects direct to terminal 15 (ignition out) of the keyed ignition switch. (Reading a '75 circuit diagram)

[andys]

I have a wiring diagram in my Clymer's manual, but it's awful small and very difficult to read the ignition switch logic, ergo my question.

Thanks,
Andys

[brp986s]

you probably know about this, but pelican has 'em here:

color coded with symbol reference

[Larry.Hubby]

Fuse #8 is the only one that is supplied directly from the switched terminal of the ignition switch (15). Fuses 10, 11, & 12 all hook directly to the battery, and fuses 1 -7 all have the headlight switch in between them and the ignition switch.

[Cap'n Krusty]

It's time, son, to buy a test light ..............................

The Cap'n

[Larry.Hubby]

I forgot to say that fuse #9 connects to the battery through a relay, the fresh air blower relay, that is switched on by the switched voltage (15) from the ignition switch. So, this acts like a switched connection. I don't know why they call it the blower relay, since it also runs the horn, and it pulls in as soon as the ignition switch is turned on.

[andys]

Larry,

So fuse #9 is switched, correct? My choices would therefore be fuse #8 and fuse #9.

Cap'n,

A 12 volt test light won't do me any good as I can't power up the system until most of the harness mod's are complete. I just figured someone here would know which fuses are switched.

Thanks guys,
Andys

[Larry.Hubby]

Andys,

Yes, fuse 9 is switched, but it's a little more complicated than I may have indicated.

First, the two fuses, F8 and F9, are different capacities. F8 is 25A while F9 is 8A, so, depending upon what you want to hook up, you might need to take account of that.

Second, after looking at the schematic a little longer, the difference between the two fuses, and the reason they drive the voltage on F9 with a relay, is that the relay isn't switched by the ignition on signal(15), it's switched by the accessory signal (X). The X signal goes on when the key is turned, but goes back off when the key is turned all the way to the start position, so whatever is hooked to F9 will not run while the starter is engaged (radios are often hooked up this way).

Third, it depends upon what year car you have. All the info I've given so far is correct for '70 & '71 cars. From '72 on, they interchanged the roles of F8 and F9. I'm not sure why. It seems to have happened when they had to add the seat belt buzzer. They don't seem to have changed the fuse capacities when they made this change, except that F8 drops down to 16A for '74 and later cars.

So, bottom line is: if you have a '70 or '71 car, F8 & F9 are on with the ignition switch, but F9 goes off when the starter is engaged. If you have a '72 or later car, it's the same thing, but it's F8 instead of F9 that goes off when the starter is activated.

[andys]

Andys,

Yes, fuse 9 is switched, but it's a little more complicated than I may have indicated.

First, the two fuses, F8 and F9, are different capacities. F8 is 25A while F9 is 8A, so, depending upon what you want to hook up, you might need to take account of that.

Second, after looking at the schematic a little longer, the difference between the two fuses, and the reason they drive the voltage on F9 with a relay, is that the relay isn't switched by the ignition on signal(15), it's switched by the accessory signal (X). The X signal goes on when the key is turned, but goes back off when the key is turned all the way to the start position, so whatever is hooked to F9 will not run while the starter is engaged (radios are often hooked up this way).

Third, it depends upon what year car you have. All the info I've given so far is correct for '70 & '71 cars. From '72 on, they interchanged the roles of F8 and F9. I'm not sure why. It seems to have happened when they had to add the seat belt buzzer. They don't seem to have changed the fuse capacities when they made this change, except that F8 drops down to 16A for '74 and later cars.

So, bottom line is: if you have a '70 or '71 car, F8 & F9 are on with the ignition switch, but F9 goes off when the starter is engaged. If you have a '72 or later car, it's the same thing, but it's F8 instead of F9 that goes off when the starter is activated.

Larry,

Thanks for the info (confusion (IMG:style_emoticons/default/huh.gif) ). My car is a '75, so it apparently uses F9 as a switched hot, if I follow your explanation correctly. The relays I need to energize (on the V8 conversion) are for the radiator fans (the gronud is switched by the PCM, and I have run separate wires for power;+12volts). Since it's low current and the fans don't need to run durring start, I suppose I can run it from either fuse.

Thanks again Larry!

Andys

[computers4kids]

Andy, how's your project going? I keep hearing tidbits and it's sounding pretty awesome.

My v8 914 is also a 75. I ran a dedicated heavy line to the fans as you have, I left my battery in the OEM position. My relays are energized by using the fuel pump cirucuit. Since you have a 75 the wiring is already there up front.

The Renegade engine wiring harness taps into switched power by removing and plugging into the relay board, which is helpful for pre 75 setups.

If you still need to identify switched power on the fuse panel, I can get my test meter out this weekend for you.
Mark

[andys]

Mark,

I deleted my relay board and changed the function of some of those exisiting 914 wires to suit what I need for the PCM controls. I still had to run 11 additional wires through the tunnel on top of that! I converted the fuel pump wire to a PCM controlled fuel pump signal wire. I don't think I'd want to risk driving three other relay coils using that wire since I'm not sure how much current the PCM can handle without causing damage.

I think my only question from Larry's posts was F8 and F9 functions and switching and of course how the '75 wiring diagram differs from the earlier models. If you could verify which one of those fuses are switched, that would be great (not to question Larry, but a verification would end any hesitation).

I'm eventually going to to start some kind of build thread or blog or (?) of my LS1/Audi 6 speed conversion. As you know, it takes time to edit and organize all the photos.

Andys

[Krank]

Andys,

Larry,

Thanks for the info (confusion (IMG:style_emoticons/default/huh.gif) ). My car is a '75, so it apparently uses F9 as a switched hot, if I follow your explanation correctly. The relays I need to energize (on the V8 conversion) are for the radiator fans (the gronud is switched by the PCM, and I have run separate wires for power;+12volts). Since it's low current and the fans don't need to run durring start, I suppose I can run it from either fuse.

Thanks again Larry!

Andys

Keep in mind, you are not directly running the device, just the coil, so the current required is less than one amp to energize the relay's coil. You should be able to piggyback any (keyed) circuit safely on the car as long as you use a dedicated power source for your device circuit (correctly fuse protected from a master buss or similar supply). Note some relays are designed with diodes to prevent feed back to RF sensitive devices like sound equipment. Just pick the right relay especially if you are going to run an electric motor like a cooling fan.