Ok guys , i have lost 2 ignition coils in my 71 in just under 900 miles of driving. The first failed when i left the key in the run position overnight. It wouldn't start and while trouble shooting it i found the resistor wire was not in use and I had 12V full time to the coil. There were several other "anomalies" in the engine harness that i found as well. I replaced that coil with an old one that i had kicking around of unknown history and placed a call to M&H for a replacement engine harness which was installed about a week after the new coil. I then drove the car with no issues for several weeks and then at the end of May just before I went to sea for 90 days it started to run like crap. It ran OK at low speeds but at highway speeds it had a skip or misfire. Anyway i parked it until i came home figuring it needed a set of points and a tune up. Fast forward to this morning. I got home from sea yesterday and went to fire up the Buicks and found the 71 wouldn't fire up. Trouble shot everything and i find the coil is grounded. I had run a test light from the battery positive to the coil neg. and had my son crank the car and test light was on constantly no flashing as i would expect. I thought maybe it was finding a ground through the tach so i removed the tach wire and it was still grounded full time, i removed the wire from the points and it is still grounded. Obviously either the primary or secondary windings are grounded through the coil case. Why is this happening? The first one may have died due to the constant 12V but i thought the resistor wire was more to preserve the points? The second coil of unknown history may have been bad but the car was still running when parked for 3 months so how did it die with out being run? I neglected to disconnect the battery before I shipped out so any electrical fault would still have been there but after 90 days the battery still had a full charge so i doubt there was current through the coil to ground as that would have discharged the battery. The engine is a very stock 70 SF code engine and everything is very original on this car with the exception of the engine harness which is a brand new M&H reproduction. I'll install a new coil Monday and grab a second for spare and keep it in the trunk until i get this figured out, I'd appreciate any suggestion the group might have to offer as to what may be causing this. Thanks in advance for the tips and suggestions:beer
110% sure there is no power going to the coil when the car is off, and less than 12v going to it when running? The resistor wire is to preserve the points life, but a constant voltage to a coil will cause them to overheat and fail, and since the coils were designed with 9v in mind, most will cook with prolonged use of 12v, but I'd expect points to wear out a few times before that happens. What is your dwell set at also? If too high it could overheat the coils as well, further compounded naturally with 12v. High dwell time could cause mis-firing at higher rpm too. And I'm not sure the test light method you used would work. Never tried it, but not sure it would work since the coil is essentially a resistor and the hot side is always passing voltage through it, I wouldn't expect the test light to blink (aka akin to putting the test light on the 12v lug of the alternator, it wouldn't light up there). Maybe remove the + side of the coil, and put the test light on the + of the coil with the alligator clip on the + of the battery. But that test will see if your points are openning and closing, but other than saying if there is a break in the coil doesn't tell you much.
Thanks for the suggestions. I found the test light on the coil neg trick on a thread here at V8 buick. I thought about it a bit after i made my initial post and thought i should dig in a bit more despite my desire to go float around the pool instead. I disconnected the positive side of the coil as well as the negative side and found that the coil was no longer grounded. I checked the pink power supply to the coil and the wire was grounded. So out comes the shop manual and we start trouble shooting. I disconnected the R terminal at the starter and still had ground on the pink wire. Then i disconnected the firewall connection, ground was then gone. I consulted the wiring diagram and found the pink wire also powers the gauges so i pulled the fuse and re connected the firewall connection and the ground was gone when testing the pink wire for the coil. i figured i had a bad sender somewhere or a ground on the gauge cluster and figured i was done for the day. So i cobbled everything back together and was getting ready to push the car back into the garage when i figured what the hell and keyed the ignition and it fired right up. then i shut it down because i hate not having any idea what the oil pressure is and figured what the hell I put the fuse back in and she fired back up and ran like a champ. Gauges all worked , everything normal. I was somewhat befuddled before now i am completely baffled but at least it is running again. This is going to rear its ugly head again I am sure. One thing i did start to think could be an issue is the 1970 engine and TH 400 . There was a wire run directly from the kick down switch on the throttle linkage to the trans before i bought the car to control the down shifting and I have no TCS solenoid in use so the under hood wiring for the TCS solenoid and the 71 type downshift are coiled up and connected to nothing. I checked and they aren't grounding so i doubt this could be contributing to the issue with ignition coil. Maybe someone who is more familiar with the TCS function and the downshift wiring could let me know if this is could be part of the problem.
