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Discussion Starter #1
This is just a curiosity question.

The other day while driving my 74 gtv, the alternator light came on bright and my oil pressure gauge went to zero.

I pulled over right away, and suspecting an electrical problem I started checking the fuses first. I began pulling out fuses and inspecting them one by one, starting on the left. Somewhere between fuse 4 and 7 (?), I found one blown. I didn't have my reading glasses so I couldn't read the value, but it was white. I replaced it with a new white one, and off I went. No further issues.

My question, after studying the diagrams, is which fuse was it. And how did it cause those two effects on my dash?

Thanks,
 

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Most likely #6 as it powers the gauges... where as #5 lights the gauges.
 

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Discussion Starter #3
My fuse blew again twice today. Any ideas to the cause? The diagrams show the fuel cuttoff solenoid through the micro switch. Has anyone seen this to cause an intermittent short?
 

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My fuse blew again twice today. Any ideas to the cause? The diagrams show the fuel cuttoff solenoid through the micro switch. Has anyone seen this to cause an intermittent short?
Happens a lot on cars converted to carbs and the wire is left loose.

Have you done anything to the car recently?
 

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Discussion Starter #5
The fuel cutoff wire might not be hooked up. If it isn't, I'm pretty sure I taped it up or zip tied it out of the way. I'll check on that tonight.

Is is safe to say that with the fuse blown (in case I run out of fuses) that I can run OK?
 

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Is is safe to say that with the fuse blown (in case I run out of fuses) that I can run OK?
Yes. Once the fuse blows, there shouldn't be any power to the circuit with the short.

the alternator light came on bright and my oil pressure gauge went to zero.....Somewhere between fuse 4 and 7 (?), I found one blown.....I replaced it with a new white one, and off I went. No further issues....My fuse blew again twice today. ...The diagrams show the fuel cuttoff solenoid through the micro switch
Whoa, tell us the whole story:

1) When the problem first happened, was the oil pressure gauge the only gauge that died? E.g., were the water temp and gas gauges registering normally?

2) The first time you replaced fuse, did both the oil pressure gauge and alternator light return to normal?

3) When the fuse blew again, were the symptoms the same as the first time? E.g., oil pressure gauge dead and alternator light glowing brightly?

4) What leads you to suspect the fuel cutoff solenoid? Is that what the blown fuse powers? What else does your wiring diagram say it powers (gauges perhaps)? And what # is that fuse?

5) Does you Alfa still have Spica? If so, is the fuel cutoff solenoid connected? Did the car start backfiring on decel with the fuse blown? And if it has been converted to carbs, what happened to the wire to the fuel cutoff solenoid?

I'm having trouble imaging what single fault would cause your only your oil pressure gauge to go dead and alternator light to glow bright.
 

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Discussion Starter #8
Unless you run out of gas or oil.....
Made me laugh! I suspected something like this was coming.

Jay's questions. It may be that more gauges went out. The first time it happened a year ago, I only noticed the alt light and the oil pressure. Those items raised my heart rate very quickly. At least the oil pressure. Once I thought about them both coming on at the same time and not related to each other, I suspected an electrical issue. I didn't drive it as much as my other Alfa all year and just started driving it more this week so the time between now and then is really only a matter of miles.

Both items return to normal with a new fuse.

Today, I noticed the alternator light and knew what had happened so I pulled over and replaced the fuse. I did not pay attention to the other items.

It is fuse #6. Diagram says defog control, gauges, reverse light, fuel cutoff solenoid. I'm thinking I may have disconnected that one and left the wire open.

It is Spica. I had installed a new pump at some point before. Rebuilt from Wes.

Thanks,
 

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So you're saying that you replaced the fuse that powers the defog control, gauges, reverse light and fuel cutoff solenoid and that made the alternator light go off? Wow, in that case, I'm stumped.

All I can suggest is examining the wiring that powers those items (decel solenoid, defog, ...). If you don't see an obvious problem, disconnect them one at a time and see if the fuse survives an extended drive. I would begin with the microswitch and solenoid in the fuel cutoff circuit.
 

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Discussion Starter #10
If I understand the alternator light, it has 12v at one end and the alternator at the other end. Is that right? If the alternator is charging, 12=12, no light. If the fuse is burned out, current could find a way to ground the other way, possibly through one of the other circuits?

I'm not sure if I was clear that the fuse blew on my way to work and when I replaced it, everything was fine for a few more miles. Then it blew again. Changed it again and made it to work.

It must be a wire touching ground once in a while. That could point to the cutoff cylinder wire which is always just hanging around the Spica pump. I've never seen a neatly dressed wire on that device.
 
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