Blowing Fuse on Accessory / Ignition Circuit

[Butch65]

Hey Gang!  

It's been awhile since I've been on, and the new look is great.  

I'm hoping to get some help with a pesky fuse issue.  At this point, we have around 7,000 miles on the car since its overhaul. It had been running great with no issues. It made a couple of 300 miles trips and everything was great.  Then in the fall we began to have issues with the 14 amp accessory fuse popping at random. It wouldn't be a big deal except that the ignition circuit appears to run through the same fuse, so we it blows, we don't go! We've had to change fuses on the side of  I-75 twice. Not good.

I searched the forum for posts on "ignition" and found a couple threads talking about the Tach wiring as a potential problem area. Rocketman rebuilt our tach, and we ran a dedicated wire to the coil.  I'm thinking I'll look for where the original wires are to make sure they are connected together solidly.  

Other than that, any suggestions on what to look for other than shorts?  

Is it possible to run a dedicated ignition circuit, bypassing the accessory fuse?  

As always, your experience and thoughts are appreciated.

Butch

 

[midlife]

Hey Gang!  

It's been awhile since I've been on, and the new look is great.  

I'm hoping to get some help with a pesky fuse issue.  At this point, we have around 7,000 miles on the car since its overhaul. It had been running great with no issues. It made a couple of 300 miles trips and everything was great.  Then in the fall we began to have issues with the 14 amp accessory fuse popping at random. It wouldn't be a big deal except that the ignition circuit appears to run through the same fuse, so we it blows, we don't go! We've had to change fuses on the side of  I-75 twice. Not good.

I searched the forum for posts on "ignition" and found a couple threads talking about the Tach wiring as a potential problem area. Rocketman rebuilt our tach, and we ran a dedicated wire to the coil.  I'm thinking I'll look for where the original wires are to make sure they are connected together solidly.  

Other than that, any suggestions on what to look for other than shorts?  

Is it possible to run a dedicated ignition circuit, bypassing the accessory fuse?  

As always, your experience and thoughts are appreciated.

Butch

There are two 14 amp fuses, so which one is it?  The one at the bottom controls the door jamb/courtesy lights/fused power lines (green/yellow wires), and the fuse above the smallest one is related to ignition, but only secondarily.  The input power is the RUN-only line, and the output is fused for things such as carb solenoid, door ajar, and emissions control, none of which should cause the ignition circuit to fail. 

I'm puzzled, because I cannot come up with a simple scenario that fits your description.

 

[Butch65]

Hey Gang!  

It's been awhile since I've been on, and the new look is great.  

I'm hoping to get some help with a pesky fuse issue.  At this point, we have around 7,000 miles on the car since its overhaul. It had been running great with no issues. It made a couple of 300 miles trips and everything was great.  Then in the fall we began to have issues with the 14 amp accessory fuse popping at random. It wouldn't be a big deal except that the ignition circuit appears to run through the same fuse, so we it blows, we don't go! We've had to change fuses on the side of  I-75 twice. Not good.

I searched the forum for posts on "ignition" and found a couple threads talking about the Tach wiring as a potential problem area. Rocketman rebuilt our tach, and we ran a dedicated wire to the coil.  I'm thinking I'll look for where the original wires are to make sure they are connected together solidly.  

Other than that, any suggestions on what to look for other than shorts?  

Is it possible to run a dedicated ignition circuit, bypassing the accessory fuse?  

As always, your experience and thoughts are appreciated.

Butch

There are two 14 amp fuses, so which one is it?  The one at the bottom controls the door jamb/courtesy lights/fused power lines (green/yellow wires), and the fuse above the smallest one is related to ignition, but only secondarily.  The input power is the RUN-only line, and the output is fused for things such as carb solenoid, door ajar, and emissions control, none of which should cause the ignition circuit to fail. 

I'm puzzled, because I cannot come up with a simple scenario that fits your description.

MidLife-

Thank you - and apologies for the long absence.  After encountering this issue we parked the car, bought the son a Subaru and sent him off to his second year of college.  The pony has been under the car cover since then, maybe getting a few mile a month on it to keep things rotating.  He's home for the summer and it's seeing a bit more daylight now - but this issue came up last night so I'm back to bird dogging the problem.

Here's what we have for symptoms: it is either one or the other that shuts us down. 

1. The fuse in the #4 fuse block position will blow and when it does, we lose the coil. Replace the fuse- and we're back on the road.

2. The coil fails.  This happened when we tried to take it for a run last night.  Cruisin' down GA 400 at about 80 and sputter , backfire, dead on the road.  Emergency call to the house, pick up a new coil, drop it in- and it started right up.

I was reading up on some of the threads related to coil specs and have to admit I never checked the resistance when putting the system together- I just followed the mechanics lead and replaced what they had installed.  

I've attached a picture of the fuse block diagram that I have been using.  I found it in the electrical manual in the data section forum.  If you look at the description for the #4 slot it calls out "electronic spark control".  



Thanks in advance for any thoughts on this issue.  

Butch

 

[Vinnie]

I have recently replaced my coil because it was blowing nr4 (thread: sparky’s got me...). After all the research (using schematics from Haynes) and discussion I concluded that power to the coil should not come from nr4 but from another wire (the one originally used).

 

[Butch65]

Thanks, Vinnie. I'll check the schematics to determine where it should be vs. where it is pulling power from.

Butch

 

[midlife]

I have recently replaced my coil because it was blowing nr4 (thread: sparky’s got me...). After all the research (using schematics from Haynes) and discussion I concluded that power to the coil should not come from nr4 but from another wire (the one originally used).

Exactly right.  The coil signal is not fused.  I suspect the OP has miswired the coil from the engine gauge feed plug, but then, how does it get the I signal when starting?  Let me guess...he has an electronic ignition module which he has not yet told us about...

 

[Butch65]

I have recently replaced my coil because it was blowing nr4 (thread: sparky’s got me...). After all the research (using schematics from Haynes) and discussion I concluded that power to the coil should not come from nr4 but from another wire (the one originally used).

Exactly right.  The coil signal is not fused.  I suspect the OP has miswired the coil from the engine gauge feed plug, but then, how does it get the I signal when starting?  Let me guess...he has an electronic ignition module which he has not yet told us about...

OK Gents, here's what I found:

After reviewing Mr.Ford's wiring diagram I see that the positive side of the coil is powered not by a R-LG colored wire, but by a RY wire.  I chased that wire back and it seems to have 2 ends, the other which has been powering the electric choke. 1 problem found. 

Sidebar 1 - Back when the engine was replaced, the mech misplaced the original engine harness so we bought a new one.   Of course a couple months later he found the harness.  We left the new one on the car and I'm using the old one to help me understand the connections and routing.  I am assuming that the wiring color codes should be the same as the old.

Sidebar 2 - We're running a Pertronix Ignitor in the dizzy. Two wires out of the cap - one to positive, one to negative sides of the coil.

Here's where I'm at :  

Found the W-BK wire that is called out for electric choke power -disconnected from RY and connected to W-BK per drawing.

Found the R-LG wire with push on connector (it had been taped off against the harness trunk).  The diagram suggests this should be on the coil + terminal.  After disconnecting the RY wire and connecting the R-LG, the car fires right up and then stops. Hmmm. Went back to the RY and it fires up strong and keeps running.  Hmmm.  

So now the electric choke is on the correct wire and the RY is only servicing the positive side of the coil.  Now I have to understand if it is part of the circuit that runs thru fuse #4.

Heading over to Mustangs Unlimited in the a.m. to grab a new Flamethrower coil and whatever shop manuals I can find to help me decode and make sure everything is good under the hood!

Butch

 

[Don C]

The reason it starts and then dies is because it is getting power from the solenoid via the "I" terminal. I'm guessing the disconnect on your R-LG wire is at the old connection to your tach. It needs to be jumpered across the connector.

 

[midlife]

Red/light green wire definitely goes to the coil. Red/yellow is fused RUN-only power lines for accessories and various indicator bulb power.

Just because a new engine gauge feed harness was bought, does not mean it is colored correctly. Ask me how I know...

 

[Butch65]

The reason it starts and then dies is because it is getting power from the solenoid via the "I" terminal. I'm guessing the disconnect on your R-LG wire is at the old connection to your tach. It needs to be jumpered across the connector.

Don- 

Can you elaborate?  Where would I be looking for the connector that needs to be jumped? 

Many thanks-

Butch

 

[Don C]

It would be under the dash and behind the tachometer. In the original configuration the ignition circuit ran from the ignition switch to a connector to and through the tach, then to the resistor wire, to a connector that connected it to the wire from the "I" terminal on the solenoid, and then to the coil. The Rocketman conversion requires removing the original connector at the tach.

 

[Butch65]

It would be under the dash and behind the tachometer. In the original configuration the ignition circuit ran from the ignition switch to a connector to and through the tach, then to the resistor wire, to a connector that connected it to the wire from the "I" terminal on the solenoid, and then to the coil. The Rocketman conversion requires removing the original connector at the tach.

Thanks, Don.  I just pulled up Rocketman's instructions and I see the jumper in the diagram. It's been a while since we did the dash work- looks like we'll be pulling the gauges to check it out!

Butch

 

[midlife]

Butch called me tonight, and we had a long chat and trouble-shooting session. To remind everyone, Butch has a Petronix 1 in his distributor, an RCCI replacement 3 wire tach in a tach dash, and a 1973. He had the dash out and wanted to know where to jumper the tach plug. He couldn't find it, but did find a pink resistor wire with an end just floating in space. Uh oh...so where's the mate on the tach plug? No plug, so we suspect both wires were cut and the mate is now buried in the re-taped underdash harness instead of spliced to the pink resistor wire. So...with no resistor wire in the circuit, either someone bypassed it (very difficult to do because you have to have the right pins on the back of the fuse box junction box, or no signal out to the coil. I think the latter, since he can start the car with the I signal but as soon as he lets off the key, it dies (i.e. no coil signal from the ignition). So...the doofus mechanic finds a RUN-only wire (now fused) and used that to power to coil. Only thing is, the coil needs an external 1.5 ohm resistor which is now missing, so that fries the coil and/or blows the fuse.

So...the root cause is buried in the underdash harness, which was not prepped correctly for the aftermarket tach. I suggested he send in the underdash, headlight, and engine gauge feed harnesses and let me sort everything out, put it all back into stock form, and he should be good to go, so long as he uses a separate line from the alternator STATOR lug to the electric choke, as Ford did for so many years.

Don't you just love folks who don't know what they are doing to muck up your car? I know I don't.

Mid.

 

[Butch65]

Butch called me tonight, and we had a long chat and trouble-shooting session.  To remind everyone, Butch has a Petronix 1 in his distributor, an RCCI replacement 3 wire tach in a tach dash, and a 1973.  He had the dash out and wanted to know where to jumper the tach plug.  He couldn't find it, but did find a pink resistor wire with an end just floating in space.  Uh oh...so where's the mate on the tach plug?  No plug, so we suspect both wires were cut and the mate is now buried in the re-taped underdash harness instead of spliced to the pink resistor wire.  So...with no resistor wire in the circuit, either someone bypassed it (very difficult to do because you have to have the right pins on the back of the fuse box junction box, or no signal out to the coil.  I think the latter, since he can start the car with the I signal but as soon as he lets off the key, it dies (i.e. no coil signal from the ignition).  So...the doofus mechanic finds a RUN-only wire (now fused) and used that to power to coil.  Only thing is, the coil needs an external 1.5 ohm resistor which is now missing, so that fries the coil and/or blows the fuse.  

So...the root cause is buried in the underdash harness, which was not prepped correctly for the aftermarket tach.  I suggested he send in the underdash, headlight, and engine gauge feed harnesses and let me sort everything out, put it all back into stock form, and he should be good to go, so long as he uses a separate line from the alternator STATOR lug to the electric choke, as Ford did for so many years.  

Don't you just love folks who don't know what they are doing to muck up your car?  I know I don't.

Mid.

Thanks for the lifeline tonight Mid! We have the dash out and will be carefully pulling the harness(es) tomorrow evening.  While the rework is a bummer, I'm glad that we've found the problem and are on the road to correcting it for good.  After this exercise, the only thing we haven't refurbished/ rebuilt is the convertible top pump - and it's next!! LOL

I forgot to mention that we're running a one wire Power Master alternator. I'm looking into alternative power for the choke.

 

[midlife]

I don't do hydraulics, thankfully. Hmmm...is this one from the rare Mach 1 convertibles everyone talks about?

 

[Vinnie]

Only thing is, the coil needs an external 1.5 ohm resistor which is now missing, so that fries the coil and/or blows the fuse.  

Flamethrower (Pertronix) coils can run off the 12 volts. Doesn't this mean that no resistor wire is required?

 

[midlife]

Only thing is, the coil needs an external 1.5 ohm resistor which is now missing, so that fries the coil and/or blows the fuse.  

Flamethrower (Pertronix) coils can run off the 12 volts. Doesn't this mean that no resistor wire is required?

Yes, I think so.

 

[Don C]

Flamethrower (Pertronix) coils can run off the 12 volts. Doesn't this mean that no resistor wire is required?

That's correct, no resistor wire for the Flamethrower, and other coils that are designed to run on 12 volts.

The reduced voltage is to reduce arcing and lengthen the life of the points, not to protect the coil. The stock coils are designed to run on the reduced voltage and still provide adequate spark voltage. Running coils on reduced voltage that are designed to be run on 12 volts will degrade the performance and spark output.