'94 Grand Am Blackout No Electrical Power

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1994 Pontiac Grand Am 3.1L cranked fine yesterday afternoon. Stopped at the library but when I went to crank it again, all electrical power was lost. As I was turning the key, the instrumental panel started lighting up like normal but ~ halfway through turning the key, everything went off. No power windows, locks, dome light, no clicking, nothing. Battery is good at 12.6V.

What should be my sequence of testing? Voltmeter is ready.

Thanks.
 
First check the negative battery cable. Follow where it goes (probably the engine block) and see if there's any voltage between that point and the negative battery post. There shouldn't be any. There should be another cable that goes from the engine to the body. See if there's any voltage between the engine and the body. Again, there shouldn't be any. If that's good, then start checking the positive cable. Follow the positive cable to the fuse box and see if there's voltage difference between there and the positive battery post. If that's good, just keep working your way downstream until you find the voltage drop.
 
Do as noted above. There's a borderline connection somewhere. Thing about those connections is that starting is always the event that sets them off, especially when dealing with a loose ground.

Start with the simple part: Battery terminals. If they are even a hair loose, they will do exactly what you are experiencing. Turn the key, blanks out.
 
I have experienced something similar in the past, could be few basic things: 1- As stated above 2- loose ground or a corroded one 3- Worst case, bad battery.

Curious, how old is battery?
 
Turn on the key and measure at the battery again. A bad battery can measure voltage with nothing connected, but then drop to near zero with the slightest load.
 
Don't measure voltage on the battery.

Measure where the battery cables terminate.

Generally, it's most likely the battery terminals are corroded.
 
I'm guessing it's a GM side terminal battery so not a lot of choice where to measure.

If you have a post terminal battery you want to measure both-- first directly on the posts to confirm that the battery itself is live, then on the terminals.
 
Battery is 4.5 years old. I've only put ~40k miles on it in that time. Yes I know that mileage isn't necessarily the issue just stating for completeness.
No corrosion on terminals. I've had that issue on my '02 Accord & learned from it.
It's an Interstate MT-75 side terminal.
Terminals are tight as I checked that yesterday (again previous issue/learning with that).
So no thoughts on it being a fuse of some sort?
 
You have a bad connection someplace. Not a fan of side terminals. Take them apart and clean them. Don't know about GMs but Ford used fusible links back then. What happens when you turn on the head lights? Check the ground strap jumping around the motor mount. Is there a jumper from the back of the engine and the firewall? Sitting doesn't do good things to cars,especially 24 yr old cars. How are the connections at the starter? AGe of the car, you're gonna get wiring troubles. wires corrode, fray at the ends where the jacket shrinks back and exposes copper.They get brittle and don't like being messed with. BE CAREFUL.
 
Positive terminal had come loose slightly. Tightened back (spec is 11 ft-lb). Started up well.
BTW, vehicle doesn't sit but rather is my daily driver due to good gas mileage (26-28 mpg).
 
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