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Car randomly losing 100% electrical power, battery testing good

Was driving one day, and when I came to a stop sign, the car just died… I couldn’t start it up, so I pushed it to the side of the road… I tried to turn the key again, and it fired right up… No issues for about a week, but then I came outside one morning, and the car was completely dead. No interior lights, dash wouldn’t light up, nothing. (no cranking noise when you try to turn the key) I assumed it was because the battery was old, and the car had just been sitting there for about a week without being started up. I was about to give it a jump, but when I opened the door, the lights came on. I put the key in the ignition, the dash lit up, and the car fired right up… No issues for about a week, until again, came outside, car was completely dead… I used my other car to run up to the store, and when I came back, decided I would try to start up the DeVille again. Randomly, upon opening the door, the cabin lights lit up, and sure enough, car fired right up… no one had touched the car while I was gone… I drove the car up to a shop near my house, where they tested the battery, which tested good. Terminals are all clean, and he made note that the ground connection to the car was also firm and clean. He offered to run a diagnostic the following Tuesday for $125. I returned home, drove the car once more over the weekend, but when I went to start the car Monday, it was again, completely dead. It’s been over a week now, and I haven’t been fortunate enough to get it to start. I again tried this morning in hopes that I would get lucky, but it’s still completely dead. I have fairly limited car knowledge / funds, so I was curious if there were any suggestions which I could try, prior to going with the diagnostic. If not, then does the $125 price seem high/fair/low? All input is appreciated, thanks !! -Jimmy

The $125 is reasonable, this covers the time for the tech to go over and check all the possibilities that could be causing this problem. It would be worth taking the terminals off the battery and cleaning the battery and cables, and putting them back on. Visually they may look OK, but there may be some corrosion in between. Another thing to check is the battery cables, they may have corrosion inside that cannot be seen. If the ignition switch were bad you should still get dome lights, not sure what else could be causing this. Your shop checked the quick and obvious things. What is the make/model/year/ miles/ maintenance history on the car?

Thanks for the feedback! It’s a 98 Cadillac DeVille. I don’t remember the mileage off hand, believe it’s around 100,000. IT was my grandmother’s old car, and was perfectly maintained until she passed away. It then sat in her garage for a couple of years. I gave it an oil change before I started driving it around, and everything has been great until this.

When a GM vehicle comes into the shop with an electrical problem, the first thing I suspect is the side mount battery cable terminals. Especially the positive cable terminals.

What can happen is corrosion can form under the red cover for the positive battery terminals. This corrosion can also leech down to where the terminals are crimped onto the cables causing poor connections.

The next time there’s no power the vehicle, try wiggling the positive cables at the battery. If this restores power to the vehicle, replace the positive battery cable assembly.


Thanks! I actually tried this last night, but a friend had suggested I do it for the negative. The positive looked good, so I didn’t really mess with it. I’ll give it another shot tonight!

If possible, remove the positive cables from the battery, and peel back the red cover to expose the terminals to see if they’re covered with corrosion.


Yes…good suggestions by Tester…as usual. Definitely check those cables out…and I also HATE those side mount battery setups…never seen anything so silly and wonder why they were ever even put into use out there.

If this ever happens again…when the vehicle seems totally dead…try the headlights and see if they function. When I read your problem description I was thinking cables and corrosion and bad connections… but then I started to wonder if this vehicle doesnt have some kind of main power Relay that is acting up… Either that or the ignition switch is wearing out inside and not making the proper connections when the key is being turned thru its course. Both have the ability to make this scenario a reality. I am leaning toward that ignition switch as the cause because this happened while you were driving it and it just shut down in that way. like the key was shut off. Seems the main power wire that feeds the ignition switch may be getting disconnected to all other sections by the internals of that ignition switch…when those contacts wear down all sorts of fun symptoms appear. It can be quite confusing if you have never dealt with this issue before. I still remember my first time with a faulty ignition switch…it was ugly.


If it’s the ignition switch, why don’t the interior lights come on when the door is opened?


The trouble is just due to a bad connection that is most likely between the battery and main distribution panel under the hood. By simply cleaning all the connections between those points, along with the ground side, using a soft wire brush you will most likely fix the trouble. It would be nice to have a test light probe you could use to verify where power is getting to. Spend 10 dollars on that and forget about the $125 dollar service fee.

Power is supplied from the battery, to the fuse panel under the hood, then to the ignition switch and on to the dash fuse panel. Since the interior lights didn’t work this means the trouble is near the battery since power for those lights comes from the panel under the hood. The brake lights are another circuit that is closely connected to the battery power source.

I had previously peeled the red cover back, and everything looks spotless! Yes, the battery being mounted sideways is extremely annoying. I will double check tonight when I return home that all these areas are clean, and also check out a “test light probe” Thank you very much for all the suggestions, i’ll report back with any new info!

I suggest you clean all the connections using a fine wire brush even if they, “look okay”.

I definitely will. I’m also going to see if I can pick up one of these “test light probes” you mentioned, are they fairly simple to figure out?

Does this Cadillac use the junction terminal located near the battery positive terminal? If so, maybe the connection there is poor. All electrical power except the starter motor windings go through those terminals and those can cause a fine one minute, everything stone dead the next type of problem.

It may even correct itself as a poor connection may come and go depending upon the temps.

To be honest, I’m not sure. I’ll have to check when I get home. I’m assuming it has to be some sort of poor connection which is sometimes making contact, sometimes not (depending on temps as you stated)

Tester…That is True…I’m really not sure if power for interior lights is fed to the ignition harness and switch before getting to the lights its possible that it lies between the fuse panel. Hell its something to look into esp since the ignition switch is associated with the delayed Off feature of the interior lights and radio (I BELIEVE) not certain but its not out of the line of diagnostic reasoning here. Plus the vehicle shut down as though the key was turned off at the igniton…which got me more suspicious of the ignition switch. Unless the shutdown was on purpose via the Security System…again ignition switch area. Anywho…the switch was something to quickly investigate…not spend all your money, or bet the farm on.

I hope that when the OP reads our or my suggestions that they use them exactly as that…“A Suggestion” Something to look into… Wont be too hard, or take too long to quickly sniff round that ignition switch. Which will lead to a Relay for the power of the interior…or Visa Versa? I dunno, just some shite to look into. I’m not sure how that “Delay Off Power” function actually works but I’m fairly certain the ignition switch has a part to play in that…since the delay off timer doesn’t begin counting down until the key is in the Off position and also removed I believe. How Cant the ignition switch be involved in that feature?

You cant bet the farm on any of us here UNLESS we say we are Absolutely Positive of what is wrong…which happens sometimes, but will be a rare occurrence while we try to help via the internet with no vehicle nearby for us to Hear, See, Smell…etc… LOL


You do realize that I have access to factory wiring diagrams?

I always look at those first when someone has an electrical problem before I provide a possible cause for the problem.


Test light probes are the easiest power devices to use. You connect the clip lead of the tester to a good ground point and you touch the probe end to the area you want to check for power. The light turns on when you have found a tie point to power. No power, no light. It’s that simple.

Oh well that’s definitely a good thing. Sorry I was just thinking out loud trying to help here without wiring diagrams handy. If the ignition switch is out of the mix…its out… Sounds good to me.


The junction terminal is usually located on the chassis next to the battery positive terminal. The heaviest battery cable will run to the starter motor; the next heaviest will run to the junction and the terminal may look something like this but with a cover over it.

SAABs also use them and can also be a fine one minute, dead as a mausoleum the next minute.

If you have a heavy keychain, more than 4 or 5 keys, I might be looking at the ignition switch.