Fuse box ground?

[70spider]

I'll check the three pin connector tomorrow. I never understood why the designers would put so many functions on one circuit, couldn't they just used a larger fuse box say 20 circuits instead of 10. That way if something does go out it doesn't cripple the entire car.

[spider2081]

couldn't they just used a larger fuse box say 20 circuits instead of 10.

Yes but on of the concepts in consider is the more parts the more possible failures so there is a balance to consider. Corroded and intermittent fuse contacts are more common than shorts and blown fuses.
There are 2 output connections on Fuse 9 One has 2 white wire in a single terminal and the other has 2 light blue/white wires. Removing the push terminals from the fuse panel should allow easy isolation of the short. Once the color of the wires with the short is determined, isolating it's location should not be too difficult. Shorts often occure withing the load or at the ends of the wires. It is much less common doe a wires insulation to be compromised leading to a short.

[70spider]

Well, I went through the all the grounds I could find and replaced an inline fuse the P.O. owner had spliced in on the pink wire leading into the ignition switch, grounded the dash, and grounded the engine. I have run him for about 30 minutes, long enough for the fan to kick on and still it all seems ok. It probably isn't but I'll run him until the issue pops up again. Well thanks for trying to help.

[70spider]

Update, the number nine fuse blew again. I used the short tester and it indicates the short is in the fuse box. It is a new fuse box, how can it be? The three connectors to that circuit look a little old but ok, no frayed wires and no melted insulation. should I get another fuse box? The mystery continues but with progression.

[spider2081]

I don't have any experience with a short tester so I won't comment on that. I think if there is a short in the fuse box causing fuse 9 to blow it should blow with the Fuse 9 output wires removed from the fuse panel. There should be 2 push terminals on the back, bottom of fuse 9 Remove both terminals from the fuse panel by pulling them off. One of the terminals should have 2 white wire and the other 2 light blue/white wires. If t he fuse blows with the wires off the fuse panel I would suspect the fuse panel. If the fuse does not blow with the 2 push terminals removed I would think the fuse panel is good.

A common cause for Fuse 9 to fail is a broken wire at the back up light switch mounted on the rear of the transmission. The wire brakes off the switch and shorts to ground.

[70spider]

The short finder is a circuit breaker that connects to the fuse box and a hand held receiver that has a direction arrow. Holding the hand held receiver over the suspected wires when the circuit breaker "pops" the receiver's arrow will bounce towards the direction of the short. In my case the direction went back to the fuse box until directly over the box the needle then stabilized. I got the idea for the tool from this video: https://www.youtube.com/watch?v=TZrCrBx ... esrealfast
I'll try your idea and check the transmission wires. Thanks

[70spider]

Update:
I did what you said and tested the fuse box without the 2 wires and it didn't trip. Then I connected the wires and tested it. For some strange reason the breaker did not trip, hmmm head scratch! I crawled under the car for shits and giggles checked the wires leading to the back-up light switch. I manipulated them a bit to inspect and nothing to dramatic caught my eye, I then checked the connectors to the switch. I went back in the car and checked if the circuit would trip, and it did, hmmmmm head bang! So I disconnected the light blue/white wires from the fuse box and tested it again, no tripped breaker. Do I dare say I have found the gremlin? Thanks for your help.

[spider2081]

Do I dare say I have found the gremlin?

I don't think you have isolated the issue to a specific part or point. There are 2 light blue/wires in that push on terminal you disconnected. I think one of them goes to the back-up light switch and the other goes to the headlight switch.
Did you at any time during your investigation put the transmission in reverse? Do you know if the fuse blows when ever the transmission is put into reverse??
There is a metal strap holding the wires to the transmission back up light switch above the switch. its possible the wire insulation chaffed through there and shorts to ground at the clamp.
I think you need to try and isolate what being powered on that causes the fuse to blow. I find writing down what I am testing helps me analyze what is happening better.

[70spider]

I agree. I am working on everything that runs off the blue/white wires. My back up switch is good, pulled it out and tested it. The wires leading to it are a bit weathered and have a few small cracks in them so I will be running new wire from inside the car to the switch and putting them in a weather proof sheath. After that I will deal with others: wiper motor and wiper motor switch, and the electrovalve, which the P.O. removed and I pilfered the 12V hot wire from it to run the electric choke on the carburetor. It will be a slog, high temps here are in the low 30's for the next week.

[18Fiatsandcounting]

I can't remember if we covered this before, but the "input" for Fuse 9 is a large pink wire, and the "outputs" are 2 white wires and 2 white/blue wires. One white wire goes to the instrument cluster to power the gauges, and the other white wire goes to the switch on the brake pedal for the stop lights.

One white/blue wire goes to the backup switch on the rear of the transmission for the backup lights, and the other white/blue wire goes to the indicator bulb in the center dash for the "handbrake on" and "brake system effectiveness" warning light. Make sure none of those leads to a short.

In some notes I have, I also wrote down that Fuse 9 powers the fan electroclutch if you happen to have that setup (somewhat rare), or from 1970 onward, the relay for the cooling fan. Not the fan itself, just the relay operation. So make sure that those wires aren't dangling somewhere and grounding out.

Fuse 9 also powered the electrovalve, but since that is removed and you are running the electric choke, I wonder if the current draw on this is too much? Unlikely, but if you ran the choke, the car was in reverse, and you stepped on the brakes, that current draw might be getting close to the 8 amp limit of the fuse.

-Bryan

[spider2081]

and the other white wire goes to the switch on the brake pedal for the stop lights.

There it connects with another white wire that powers the solenoid of the coolant fan relay. So in early Spiders the ignition switch needs to be "on" for the coolant fan to run.
I think the electrovalve is a solenoid and it probably would draw much less current than the choke. I am not sure but I don't think either the electrovalve or the choke draw current for a long period of time. Does the fuse blow instantly upon turning on the ignition switch?
If the fuse only blows with the light blue/white wires connected to fuse 9 then I don't think the coolant fan circuit would be the issue.
The light blue/white wire are used in the turn signal (though the hazard switch), electrovalve, brake effectiveness light and back-up light circuits.

[70spider]

Update:
This is where I stand, I repaired the wires going to the back-up light switch and the issue is still there. I used the short locator and it led me to the pigtail connector in the driver side panel. I disconnected the pigtail and did a continuity test from the connector to the fuse box and it came back with a 0.4 on the 200 ohm setting. With the pigtail still disconnected and the light blue/white wires connected to the fuse box I turned the key on and it tripped the fuse. While the circuit breaker was popping I used the direction meter and it leads to the pigtail ????????? if the continuity is ok why would it still trip the fuse? At this point I might just get some dynamite and blow the #$@@@%$^&&$ car up.

[spider2081]

I am having trouble following what you are doing. I believe when the push connector with the light blue/white wires is removed from fuse 9 the fuse does not fail. Is this correct? When the light blue/white wire terminal is connected to fuse 9 the fuse does fail. Is that correct?
One path for the light blue/white wire is to the hazard switch. When the hazard switch is in the "off" position fuse 9 power passes through the hazard switch to the turn signal flasher. When the hazard switch is in the "on" position this power is not used and battery power fuse 1 (hot all the time) power is switched to the hazard flasher.
Have you disconnected the turn signal flasher to see if Fuse 9 blows?
Do the Hazard lights work?
Have you visually inspected the wires on the Hazard light switch? The light blue/white wire combines with a yellow/black at the dash brake warning light. So a yellow /black wire on the hazard switch would be power from fuse 9

hope this helps.

[70spider]

I am having trouble following what you are doing. I believe when the push connector with the light blue/white wires is removed from fuse 9 the fuse does not fail. Is this correct? When the light blue/white wire terminal is connected to fuse 9 the fuse does fail. Is that correct?

Yes blue/white wire removed = no fail when connected = fail.

One path for the light blue/white wire is to the hazard switch. When the hazard switch is in the "off" position fuse 9 power passes through the hazard switch to the turn signal flasher. When the hazard switch is in the "on" position this power is not used and battery power fuse 1 (hot all the time) power is switched to the hazard flasher.
Have you disconnected the turn signal flasher to see if Fuse 9 blows?

Wow, I didn't see that the flasher was connected but looking at the wiring diagram again it is all connected thru the indicator lamp.
So, Yellow/black is goes from the emergency flasher switch to the Brake system effectiveness and hand brake ON indicator lamp. Also connected to the lamp is the blue/white wire from #9 fuse, and the white/black wire runs from the indicator lamp to the hand brake switch.
So with all that in mind, I tested the hand brake switch it is good (0.4) however the black/white wire going from the pigtail to the hand brake switch reads 01.5 on the 200 setting (is this bad?). I will test the indicator light and the e-flasher switch tomorrow (although it is virtually new, replaced it before I rebuilt the engine).
Well thanks for the help, I am use to 1960s Fords so this is a mess.

[spider2081]

the black/white wire going from the pigtail to the hand brake switch reads 01.5 on the 200 setting (is this bad?).

The Light blue/white supplies voltage to the Brake effectiveness light light. the White/black wire supplies the ground for the light to light. The white/black wire can only light the light it can't blow a fuse if shorted

I am not a fan of measuring resistance in auto circuits. There are too many sneak paths for the meter to be reading and it can be confusing. I prefer voltage measurements. Of course with a blown fuse you don't have voltage to measure. So if checking resistance try your best to know your are checking just one wire or circuit.