Ignition coil fuse blows the second I turn the key on

[tevans720]

1980 Mustang w/68 302 points dizzy. Everything was working fine on Tuesday night. Wednesday afternoon I go to start it and it turns over with no fire. I'm in the middle of a dash swap finished all the wiring on Tue. night and everything was working fine. I put a charger on the battery cuz I was turning lights on and off alot during wiring. Well Wednesday morning I got the key out of it and realized I left the key on all night with the charger hooked to the battery. Don't know if that would have anything to do with it. I don't think so the battery never died.

Well anyways Wed. afternoon I traced it down to a blown fuse. I threw another in and pop right when I turn the key on. So I pulled the wires off the coil and put another fuse in. Turned key on and fuse was fine. I hooked the + up then the - for the tach. Still the fuse was ok. Then hooked the - from the dizzy. Instantly the fuse blew.

I traced the wire from the coil to the dizzy and it looked fine and tested it with a multimeter and the wire was fine. I looked in the dizzy to see if anything by the points were touching that are not supposed to and that was fine. So I started to follow the + wire. Followed that through the firewall and it splits through a harness. One to the fuse box the other to the cluster. Since I just was repinning the cluster I double and triple checked the wires all fine and all hold power fine. Also none were crossed or bare or anything like that.

So I swapped coils and the fuse was fine. Tried to start and still no ****ing spark. WTF! so I look at the coil and that thing was so hot I could hardly touch it. As fast as I could I pulled the wires off.

The only thing I can think of is I have a short somewhere by the cluster. But it worked fine Tue. at midnight and 14 hours later it don't and no one has touched it at all.

Thanks and please help I'm getting sick of wiring.

O forgot to add points were replaced 2 weeks ago.

 

[tevans720]

Well can someone just start throwing stuff out there. I have been over things like 20 times. Blowin over 100 fuses. I bypassed every wire hooked straight to the battery with a fuse in-between and right to the dizzy with a new wire. Still blew the fuse. new coil different dizzy still all the same.

I'm about to start slamming my dick in a sliding door to see if that helps. HELP!

 

[tevans720]

ok another hour goes by and still know one can help

 

[jrichker]

Check out AutoZone's self help. They will have wiring diagrams for you car. The original ignition system had a Duraspark box that did not use points, so your wiring may be different from stock.

See | Repair Guides | Understanding And Troubleshooting Electrical Systems | Understanding And Troubleshooting Electrical Systems | AutoZone.com for wiring diagrams.

If I remember correctly, the 60's-70's era Fords had a ballast resistor in line with the ignition coil. It dropped the 12 volts down to 6-8 volts to match the ignition coil's voltage requirements. If it got bypassed or mis-wired, it would cause the problems you are describing.

 

[tevans720]

Ill try putting this in.

http://www.napaonline.com/Search/Detail.aspx?R=ECHICR11_0195056800

Click shop online or put in your zip and it will show the part

I hate Napa with a passion but I gotta get it done.

Will this work I know it's a resistor wire in mine but this will work like that won't it?

 

[tevans720]

Oh yea forgot to add when the fuse holds I check the + coil wire I'm getting 12 volts. So I must have skipped the resistor.

With the resistor installed correctly I should get 6-9 volts at the + coil wire correct?

 

[jrichker]

Oh yea forgot to add when the fuse holds I check the + coil wire I'm getting 12 volts. So I must have skipped the resistor.

With the resistor installed correctly I should get 6-9 volts at the + coil wire correct?

Yes.... BUT only when the points are closed or you ground the points side of the coil to battery ground or the engine block. Approximately half the voltage will drop across the ballast resistor and the other half will drop across the coil. Voltage drops are measured by placing one meter lead on one side of the item under test and the other meter lead on the other side.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for more help on using a DMM to test automotive circuits.

The voltage drop across the ballast resistor only happens when there is current flowing through the circuit. When there is only the current used by the Voltmeter, the voltage will still read 12 volts. I am sorry that I don't have a simple non-technical explanation of voltage drops in a loaded series circuit compared to a non loaded series circuit at this time.

 

[tevans720]

I have no idea of whats going on. I put a new resistor in and that thing got orange hot and started smoking like crazy. That can't be normal. I have check the wires time and time again. No open, cut, or shorted wires. I have followed all the wires to where they go and there was NOT a resistor, or resistor wire for any of the ignition components. Only resistor wire that in the whole car goes from the ign. switch to the wipers.

I have also found out that when the points are open the fuse holds fine. The second they close the fuse blows. The only thing I can think of is to replace it all. Points, condenser, cap, rotor, coil, and wires. But still don't make sense to do that cuz I have dropped in a different points distributor and have the same issue. As soon as the points close the fuse pops.

This is just horrible my truck rear end decided to take a crap so now I'm left without a car.

 

[jrichker]

Here's a diagram of what it should look like. The fuse can be first in the circuit or the ballast resistor can be first in the circuit - the order of fuse and ballast resistor isn't important.

Note that you will need a 1960-70 Ford ignition coil to get the resistance in the correct range. The later Duraspark and EFI coils all had much lower primary resistance value. The lower the resistance, the more current it draws. The current draw should run between 4-7 amps to avoid overheating the wiring and burning up the points.

 

[tevans720]

Ive tried running the resistor wire straight to the + on the coil. The resistor wire started to warm up. So I pulled it off before I did any damage. Now I read somewhere that the wire is supposed to warm up cuz of the resistance. Is this true? Cuz I'll do this again if I'm not gonna burn the wire up.

 

[jrichker]

The wire is supposed to be protected by a fuse. Use the proper fuse for the wire size as shown in the drawing I posted and it will be OK.

 

[tevans720]

ok wish me luck then im off work in a hour and a half gonna do it right away.

 

[tevans720]

Traced everything down to the coil. Coil was shot just never heard of a bad coil blowing fuses though. Well went out and got a MSD coil and resistor kit. Installed and fired right up. I can't figure out how they did it before me there wasn't a resistor anywhere near to coil or wires.

Well I thought I'd ask you cuz you seam like you know what your talking about. That resistor gets so hot you can't touch it with out burning your self. I have read that it's supposed to get that hot but you know how trust worthy the internet can be. ha ha.

Thanks again for all your help.

 

[jrichker]

Traced everything down to the coil. Coil was shot just never heard of a bad coil blowing fuses though. Well went out and got a MSD coil and resistor kit. Installed and fired right up. I can't figure out how they did it before me there wasn't a resistor anywhere near to coil or wires.

Well I thought I'd ask you cuz you seam like you know what your talking about. That resistor gets so hot you can't touch it with out burning your self. I have read that it's supposed to get that hot but you know how trust worthy the internet can be. ha ha.

Thanks again for all your help.

The resistor will get too hot to touch. As long as the proper size fuse is used and the fuse doesn't blow you are OK. See the diagram I posted for fuse & wire sizes.

 

[tevans720]

Thanks again for your help. If the car is running the resistor is not hot. But I mounted it away from everything anyways.