• 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
What might cause constant "on" at coil?
Something has happened to my ignition system. I noticed a completelky dead battery, and while charging it, noticed that my coil got really hot.

Turns out thewre is constant power to the coil even with the ignition switch turned off.

I know this could be a bad ignition swith itself, but do any of you know the best way to diagnose this gremlin? I hate to tear into the steering column if this may be a more common issue such burnt out relay or ground somewhere.
I'd start by replacing the starter "solenoid" (it is really a relay) as if it is malfunctioning it might account for your symptoms, it is cheap, and it is easy to get to.

If your coil got that hot I'd also plan to replace it once you get everything corrected.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
I had one do the same thing and it was the solenoid that was the culpret
Thanks. I'll start with that. So in regards to the selenoid... Since I have upgraded to duraspark with a Accell Super Coil, will a 70's are OEM type replacement selenoid be OK or should I be looking for something more from the mid to late 80's?
The OEM part should be fine. I ran the same coil with the OEM solenoid back in the 70s without a problem. Chuck
It is really just a great big relay.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
The more I think of it, I don't know that the selenoid could be the problem. My mechanic buddy (who ran out of time helping me) snipped the wire coming from the ignition switch... snipped it yet the lead coming from the switch was still hot. I think that would eliminate the selenoid being the issue wouldn't it? Maybe not because of other hot wires going somewhere out of the selenoid that aren't supposed to be hot??
The I post of the solenoid supplies 12 volts to the coil during start. When the key is released the coil receives 9 volts from the ignition switch through the 'pink' resistor wire. A damaged solenoid can indeed cause voltage to flow to the coil and 'backfeed' all the way to the switch.
The easiest test is to pull the small brown(?) wire off the I post of the solenoid and check that voltage at the coil drops to 0.


Tachs, Voltmeters, Headlight kits, Wiper delays and more at
[Image: smlogo.jpg]
Rocketman's Classic Cougar (and Mustang) Innovations, LLC
When I look for an electrical drain, the first and cheapest thing I do is start pulling fuses.. it doesn't cost anything..

Leave the negative battery cable loose on the battery, but snug so it will conduct voltage.. When you pull it off and on, there will be a noticeable small spark, indicating a power drain.. With the cable snug, pull a single fuse and then slowly remove the battery cable. If you still have a small spark, that circuit is not the problem.. Repeat the procedure, one fuse at a time until you get to the one where there is no spark at the cable end.. That will be the circuit with the issue.

Trace the wiring back from the fuse panel to the switch, light, radio, clock (you get the idea) that is causing the problem..

Hope this helps.. It might save you some $$...
OK, so with the old coil removed (it was cracked from over-heating while charging), AND the ignition wire snipped...

I connected the battery. Used a volt meter with the negative probe on the negative battery stud. There was 9 volts coming from the firewall side of the ignition wire. The other wire from solenoid to coil was disconnected from everything.

Looks like my ignition switch isn't turning into the off position, or I have a short somewhere.

I wish we weren't going out of town this weekend... I'd like to get this straightened out.

Thanks for all your advice, guys! Keep it coming, and if the weather turns bad, maybe I can talk the family into coming home early since boating will be out of the picture.
Share Thread:  

Possibly Related Threads...
Thread Author Replies Views Last Post
  351 cleveland battery to coil wire resistor DeereFanatic 6 290 02-27-2019, 03:31 PM
Last Post: batwrangler
  New ignition coil question. Sumit 8 1,290 05-24-2017, 10:07 PM
Last Post: Don C
  tach bypass, resistance wire, coil pwr SteveO_71 1 832 03-20-2016, 01:03 PM
Last Post: jbojo
  powering the coil Omie01 5 1,313 03-28-2015, 08:56 AM
Last Post: Don C
  Slight confusion with coil/dizzy Omie01 1 604 02-15-2015, 08:55 AM
Last Post: c9zx
tach No Spark from Coil hetrickw 12 1,919 07-18-2014, 02:23 PM
Last Post: 72HCODE
  Couple of Coil Questions goodnigh 15 2,297 06-17-2013, 12:10 AM
Last Post: Wolverine
  Mustang Coil Spring Compressor marks73 20 5,554 02-26-2013, 12:46 AM
Last Post: gpierce

Users browsing this thread: 1 Guest(s)