I have a 76 F100 that has an aftermarket electronic ignition system that worked very dependably for 3-4 years. I have a transplanted 390 that has a distributor w/ a Crane optical triggered XR 700 that was triggering an MSD 6A through an MSD coil. This past spring I developed an intermintent problem that in effect was killing the motor as if the power to the ignition was shut off. I've tried using other coils, replacing ignition wires, removeing the MSD 6A. Sometimes the problem only acts up a little, sometimes I can't start the truck for days. Currently I'm looking at the ignition switch. A pale red wire w/a green stripe on it that is in the ignition switch harness is getting very warm when the ignition switch is on. I just tried a brand new ignition switch and its still getting very warm. When I have problems it always crops up only after the truck has been running between 5-10 min. Any ideas where this wire goes to or why it might be getting hot? I did have a radiator issue this spring where a mist of radiator fluid was coming out of the radiator and spraying around the front of the motor. Could I have a bad fusible link near my solenoid? Help? I'm on a tight budget and don't want to have to be replacing things on a hunch that aren't bad.

BBT

 

That wire is the resistor wire for the primary side of the coil. It gets warm during operation.

Antifreeze must be washed off the secondary ignition system immediately. Antifreeze forms a high resistance leak path for the secondary. Once a leak path has formed it burns a carbon track into the insulation which will continue to leak off the spark energy. Antifreeze also forms a leak path on humid days or in other wet conditions. Once your secondary insulation system has been damaged the only thing that can be done is to replace any component contaminated by antifreeze, wires, cap, coils, even plugs and the rotor at times.

 

Big,
Intermittent failure at temp could be the pickup stator in the distributor. it won't neccessarily fail the same way twice. Diagnosis can be very difficult, and obiviously maddening.
Secondly, if spark plug wires are failing, you can diagnosis by spraying a light mist of water on them in the dark. You may be able to see the arc to ground.
Good Luck,
KingFisher

 

I learned something this afternoon. I started the truck this afternoon. And not surprisingly it quit on me. The temperature around here is in the 80s and the symptoms seem to crop up in the heat. The first time it quit I quickly restarted. The second time, I couldn't immediately restart. So I took my voltage tester and found that I was only getting 4-5 volts at the switched terminal of the solenoid. After a few minutes, I was able to restart and get home. At home, I was able to test again and see that I was getting 7-8 Volts. Then I watched it quit again w/ a voltage drop. Now my aftermarket ignition, the Crane XR700 needs about 8 Volts and gets it's power along w/ the coil from the switched terminal of the solenoid. My volt gauge tapped in my fuse box is getting a healthy 14 Volts. Regarding the resistance wire that is getting hot near my ignition switch, being as I am not using the original Ford Duraspark ignition, should I disconnect it? The coil is getting power directly from the starter solenoid. The plug wires and coil wire are brand new. I haven't replaced the cap or rotor yet. I believe the root of the problem is the lack of voltage at the switched terminal of the solenoid. In the past when testing things, I've had 11-12 volts at that terminal. The Crane/MSD wiring worked well for about 2 years, and the Crane as a stand alone worked flawlessly on an older truck.

BBT

 

The coil gets power from the "I" terminal on the starter solenoid in START but in RUN the coil power comes from the ignition switch thru that resistor wire.

 

On my aftermarket ignition, the only power going to the coil comes from the wire I installed from the "I" terminal on the solenoid. The Crane box takes unswitched power and switched power, and the coil gets power from the same switched power source. The old duraspark stuff hasn't been used in over 2 years. I replaced the solenoid and at first I was getting 8 volts at the switched I terminal, then at the end of the block on the test drive, it quit again. I got it back into the yard and parked it for the day. Now I wonder why the battery reads 13.5 V yet the I terminal only 8Volts? Is the alternator involved? I do have a one wire GM style alternator I used on my old 69 Pickup after hogging out the hole for Ford use, that I could make use of again to replace the regular Ford alternator that I've been useing for several years. I remember that with that I had to find the right wire in the harness in addition to the "one wire". It worked fine along w/ the same Crane box and distributor when it was all in the 69 truck. I'm thinking that my alternator probably got bathed in alot of radiator/coolant mist when I had the leaky seam in that upper corner of the radiator near the alternator. When I started the truck cold after installing the new solenoid, the battery read 13.5V, the I terminal 8V, the +side of the coil 8V. Running, the I terminal was still 8V and the same w/ the +side of the coil. According to Crane, this is a minimal Voltage to run the system.

BBT

 

The "I" terminal is not connected to the battery unless you are starting the vehicle. It sounds like you still have the + coil running off that resistor wire and possibly your ignition box too.

 

Here's the latest. I took my electrical tester to the solenoid. The "I" terminal has two wires hooked to it. One is my switched power feed that goes to the Crane Box and is Y'd to the positive side of my MSD Blaster coil. The other is from a wiring harness under the hood. I took that wire from the wiring harness and removed it from the solenoid and checked the voltage with key switched on. It was getting 12.02 Volts. I then reconnected to the solenoid, it read about 8 volts. I then removed the feed to the coil and box, the I terminal then read 12 volts again. Next I reconnected the feed to my coil and box to the solenoid and took the + feed off the coil. That wire that goes to the + of the coil was nearly 12 volts.. 11.something. So it appears that the coil itself is draining voltage from the system. Maybe it is suppose to? I did go feel the wire from the ignition switch that had been on for several minutes. It wasn't hot like it's been. So I'm thinking my coil is bad. The auto parts store is asking about whether the coil is externally or internally resisted. They say the MSD coil is suppose to have an external resistor. Should I get a new MSD coil along w/ an external resistor for it?

BBT

 

First of all you need to know Ohms law among other things to troubleshoot an electrical system with a meter like this. I don't have near enuf time to walk you thru basic electricity. There are books on the subject but they all take time to read and study. Your best bet is to find a friend that knows electricity and electronics, and no I don't mean the friend that can hook up a stereo or computer. My son can do that but he knows nothing about electricity.

Troubleshooting is one of the reasons why I recommend people stay with the factory ignition system. The OEM DS-II system is way better than aftermarket systems.

From what I can tell in your posts your aftermarket system is hooked up incorrectly. I can move this post to the Electrical Systems forum but you still need to find a qualified electronics tech to work on your vehicle.

 

I've re-wired in my MSD box and the voltages at my "I" terminal I'm getting switched power from are normal again, and the wire off my ignition switch is no longer getting hot. And often the truck runs strong. But it's quitting again randomly and I've performed a test to determine if the optical sensor might be bad and it appears that it may indeed be the optical trigger that is intermintent. When I trigger the MSD/coil by tapping a screwdriver on the two wires that leave the optical trigger, I get good strong spark. So I call Crane about a replacement optical trigger. They suggest a new two wire optical trigger that eliminates my XR700 box and triggers my MSD directly for about $34. I'd really like to go to a magnetic triggering distributor. I know that there are a few Duraspark distributors found in 75-76 FE's. And some pricey aftermarket billet distributors from MSD, Accel, and Mallory that are in the $300+ price range. Any suggestions of whether a magnetic trigger distributor such as Mallory's are worthwhile in their improvements, or how hard it would be to find a late FE distributor?

BBT

 

To answer your last question, usually people buy the aftermarket distributors because they want to be able to play with the timing curve more easily. You can use a duraspark II distributor out of a 360, and then go to MSD's site and there they tell you how to use it to trigger the MSD box. But you will have a stock advance curve which may or may not be to your advantage as far as power is concerned. You can play with the stock Ford dist, but you have to take it all apart to do so.

I don't know how you finally wired your ignition up, but it sounds like it was wired correctly in the first place. And I hope you realize, unless there is something screwy with your solenoid, that you are not getting switched running power from the "I" terminal. To prove this, take all wires off the "I" terminal, and then check the "I" terminal for voltage with the key in "run". There will be no voltage there.

The voltage drop you where seeing was indeed from the resistor circuit from the red/lightgreen wire. Read the instructions for the coil you are using, but most coils do require a resistor. If your set-up does require a resistor, then you need to use it, or it will overheat the coil and put a lot of strain on the box. Just make sure to check to see if MSD requires a resistor.