Anxious about electrics - relay fused?

[phaetn]

I have never had a working lighter or hazards, so I used the cigar lighter hole to run wiring for an iPhone holder (power and 3.5mm headphone jack) when I installed a new dash cover and console, and just hid the hazard switch that didn't work properly. The iPhone gets it power through the radio.

Thinking ahead to the drive to FFO, I thought it would be useful to get an external 12v accessory adapter and would mount it somewhere near the manual throttle knob. The device just needs 12v and a ground.

I thought maybe I could use one of the purple wires for the inspection light socket since they aren't plugged in to the receptacle; no juice. Argh! That would have been too easy!

I see two inline fuses under the dash. This is consistent with a '74. One has an 8amp fuse installed with red and black leads. According to the '74 wiring diagram side 1 (thanks for hosting this, Brad!!) this is for the lighter; the red is hot to the lighter, the black wire goes to fuse A, from which a violet wire goes to the inspection lamp socket. No juice from this inline fuse. This makes sense based on what I have already been seeing, and presumably there's a disconnect somewhere. Too bad I can't use it, but I'm not about to take the dash apart to figure it out.

The other inline fuse has a 20 amp fuse in it that is blown. It has a single pink on one side, double pink on the other. The inline fuse itself looks quite aftermarket as it's orange. Again, according to '74 wiring diagram side 1 this should be for the fuel pump relay. But my pump still works even with the busted fuse. The one side is hot -- I used a voltmeter and got about 11.6v. So I know this is a good wire if I need it for the 12v accessory socket. I've replaced the fuse and now know that the other side is getting power but I don't see any difference in the functioning of anything electrical. The diagram shows one of the double pinks goes to the thermostatic switch (which seems fine) and the other to fuse box item I which, with a white wire, eventually goes the the fuel gauge which seems to be working fine (though I'm not yet sure about the low fuel light.

When I put the key to ON (not start) I could hear the fuel pump, as always. I have disconnected every fuse, both in the array and the two inline ones, and I couldn't get it to turn off. Is this a concern? Is it okay that the pump is always unfused? Is the fuse really just meant for the relay that then connects to other stuff?

Meanwhile, can I just use the pink wire that's hot and -- running a totally new and separate inline 16amp fuse -- use that for my 12v adapator? I know it would work, but I don't want to in any way affect the load that might be supplied to the fuel pump as this is critical for car operation. On a test run with the fuse replaced the car still seemed to run okay, but I also don't want a leak that might drain the battery given that everything seemed to run okay even with the blown fuse...

Everything that I need to work -- lights, turn and brake bulbs, instruments, radio, horn, fans (engine and heater) -- all work fine so I'm reluctant to mess too much with wiring. Should I be concerned that there's a blown 20amp relay purportedly for the fuel pump relay and that the pump clearly still works without it? Can I draw from it?

I guess things are always tricky with electrics. I know the previous owner installed Hella H4 halogen lights that run of a relay, so clearly everything isn't original, and he had the brown wire fix done.

Any help/suggestions would be much appreciated!


Cheers,
phaetn

[wizard124]

Aren't electrics fun?

I took a look at the Artigue diagrams to try to help you out.

On page 2, the green/black hot from the fuel pump shows a second wire running out from a connection block to the ignition switch. It appears the pump is not fused and runs coninuously when the ignition is on. The other wire runs to the fuel pump relay, it is also green/black. I don't know this relay's location It would be easy to check if this goes hot with the key in run; match to schematic?

[wizard124]

Question

Are the Ignition Relay and the Fuel Pump Relay (shown in the diagram) really switching relays? Or are they merely junction boxes that split and direct current? The diagram is hard to decipher without really studying it. For instance, if the contacts at the ignition switch were labeled "OFF", "Run", and "Start", it would be easier to understand how it all is supposed to function. Same with the input and output of the relays.

How is the brown wire fix done in your car? Maybe this has something to do with why some circuits are still functional with the fuses blown/pulled.

[wizard124]

You mentioned the black wire from Fuse A, which runs to the hot side of the in-line fuse is cold. Fuse A gets its juice from the Alternator and Starter.

I would remove the 2 screws holding up the fuse panel. This allows you to lower this wire bundle to have a better look. What is behind fuse A? Is the black wire pulled or snipped? Any splices? Might be an easy fix! Then you can enable the inspection light socket through the fuse.

This light socket is wired for higher draw making it a good choice for your assessory adapter. If you are looking just to recharge a phone or use some other minor amperage electronics, I would say you can splice in most anywhere.

[phaetn]

Thanks for the replies and studying the diagrams, wizard124. Another set of eyes really helps!!

I, too, am somewhat confused as to the function of the fuel pump relay. What does it actually do? Is it actually a switch, or merely some sort of junction?

Good news that the fuel pump is always live if the ignition is on. I suppose in later years they must deal with that in case of accident so it doesn't just keep pumping fuel even if the ignition is on but the car/motor is otherwise non-operational. Is that why there is, in fact, a relay?

Apart from the headlight relay and brown wire fix, the other bit of custom electrics I have is that the car no longer has a distributor, but the Gen. 1 CompuTronix igntion (which has its own set of relays in the engine bay).

I can definitely pull down the fuse box and check behind it. I was a bit reluctant to do this in case:
i) I somehow pulled on some wires and messed up a connx
ii) if I do make the violet wire live that it somehow causes a short because the ball of mess that is the hazard wiring switch isn't properly connected/wired itself, and I'd have to pull the dash/console to get at it.

Now that you've assured me that the fuel pump isn't fused, I'm tempted to just use the double pink hot lead, especially given that everything still works on the car even with the inline fuse blown that goes to the single pink (and links to the fuel pump relay according to the wiring diagram); replacing the fuse hasn't seemed to make any difference to functionality that I can tell... That means I could take the fused side out of the loop, and have it go to my custom accessory instead...

Thanks again and cheers,
phaetn

[toplessexpat]

Hey - before pulling the fuse box, disconnect the battery! Eliminates the chance of shorting. Use the continuity tester on your multimeter to check for connectivity from the fuse box through the car, instead of looking for +12v. Ok - depending on where in the circuit your are you can't see circuits that are relay switched - but it'll be safer when dropping the FB, and you can always move "downstream" of the relay. As a good friend says.... "Electricity is like water", so if it's not flowing something is stopping it. Brads wiring diagrams are a great start - although it sounds like you've had a fair amount of modification in your cars history. Accessories are one thing - but hazards are always needed!

A

[phaetn]

Thanks for the tips.

I know not having hazards isn't great. So I have two safety triangles: one to hang from the trunk, and one with a base to put on the road. Plus I have flares. The cars are so low I want mine seen from a distance if I have to pull over and stay there.

As for at the moment of trouble, I guess I'll just have to wave people around.

Cheers,
phaetn

[toplessexpat]

I feel that my next work trip to Toronto may include a diversion over to Ottawa!

[spiderdan]

may include a diversion over to Ottawa!

If you do, poutine and beers on me.

[phaetn]

I feel that my next work trip to Toronto may include a diversion over to Ottawa!

Totally! Hopefully it will be a lot warmer then the last time you were in the Great White North.

Cheers,
phaetn

[toplessexpat]

I hope so.... -40F wasn't pleasurable!!!!