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Sparky’s got me. It’s the coil. Why?
#1
Hey guys,

My fuse nr 4 kept blowing today after I had a nice run. I came back, turned it off, gave the car a clean and when I wanted to drive it inside, ignition was gone. Upon closer inspection fuse nr 4 was blown again.

I replaced it twice but it blows as soon as the key hits ON.

In the past I replaced the turning signal wiring and I have added 1 wire to operate the solenoid on my pmgr starter. Both work fine.

My Haynes book says fuse 4 is for: indicator lights, oil pressure, engine water temp, dual brake system, seat belt warning lamp and buzzer, emision control solenoids, throttle solenoid positioner, electronic spark control.

I have no idea where to start investigating this issue. I kind of know about all those things the fuse is for but I have no idea where thewires for them are.

If I want to tackle this issue, where should I start? What would be the things to look into first?

Any pointers would be appreciated! In the meantime I’m going to study some schematics I think...

Thanks for any helpful ideas!

Vincent.
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#2
Disconnect your dash cluster and start the car (assuming you have no tachometer). The oil pressure, brake proportioning valve, and temperature bulbs in the dash may be shorting to ground. If the fuse still blows, disconnect the blue square plug for your seat belt indicator lamps in the engine compartment, near the NSS/BU switch. Those wires may be pinched and shorted to ground. The other three purposes/wires are rarely used today.

Let me check your shorts!
http://midlifeharness.com

[Image: Flamicon2.jpg]


[Image: oldfart.png]
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#3
Is there an easy way to disconnect the cluster? Last time I worked on it I removed the steering wheel and took the cluster out...
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#4
I would start with the wires in the engine compartment, easier to get to.

Did you repurpose any of the wires, like using the throttle position solenoid wire for electric choke?



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#5
There was an electric choke in use when I bought the car (still is), I I don’t even know what that solenoid is or where it is located, let alone which wire was connected...

Here’s Haynes on nr 4 btw:

[Image: a0423a4dbe9009b9a79c66f3c5829b6e.jpg]
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#6
(06-09-2018, 03:36 PM)midlife Wrote: Disconnect your dash cluster and start the car (assuming you have no tachometer). The oil pressure, brake proportioning valve, and temperature bulbs in the dash may be shorting to ground. If the fuse still blows, disconnect the blue square plug for your seat belt indicator lamps in the engine compartment, near the NSS/BU switch. Those wires may be pinched and shorted to ground. The other three purposes/wires are rarely used today.


I got brand new cluster printboard and I replaced a bunch of bulbs with led versions a few years ago.

What/where is the nss/bu switch?
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#7
(06-09-2018, 04:50 PM)Don C Wrote: I would start with the wires in the engine compartment, easier to get to.

Did you repurpose any of the wires, like using the throttle position solenoid wire for electric choke?

Vinnie,
what Don is saying makes pretty good sense.
I would hook up a circuit breaker up in place of that fuse and start targeting the loads of that circuit.
you have more solenoids on that line than meets the eye.
get the ones in the engine compartment first.
then the warning buzzers.
after the major players are eliminated it comes down isolating the circuit (opening up splices)
no one wants to do that on a car that is almost 50 years old.
Boilermaster
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#8
I have ordered a circuit breaker to do further testing.

Where abouts should I find that blue connector?

Also, could this somehow be temperature related? All the times the fuse blew was when the engine was warmed up...
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#9
If you have a 1971, you may not have a blue connector, as it was introduced mid-way through production. It is located in the engine compartment, near the neutral safety switch/backup plug, the engine gauge feed (oil, coil, water) plug, PRNDL lamp plug near the firewall on the back side of the engine.

Let me check your shorts!
http://midlifeharness.com

[Image: Flamicon2.jpg]


[Image: oldfart.png]
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#10
Before start doing any dashboard sport or get headaches reading diagrams, i'd put back the fuse and connect to a voltmeter at this #4 start the car, and observe if voltage is constant or fluctuates with rpms.

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
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