New Battery but starting being prevented
 

I believe I've read thru the (many) threads on battery drain but I haven't found my particular issue. I originally thought my 1990 C4 was afflicted with the 'classic' battery drain* but having replaced the battery and been a bit more observant of the specific symptoms I now suspect that there is some electrical gremlin that is actively preventing start. Here is what happens:

Newly connected fully-charged battery - starts once and can be driven. Once it is turned off, on next start (even a minute later) dash lights flash and then there is a 'click' and then nothing. No attempt to start. Then the power from the battery seems to be shut off altogether. Nothing happens on key turn. Interior lights don't turn on. the voltmeter plugged into the cigarette lights goes dark (was 12.5 before last start attempt and 14+ during last drive). Now if I disconnect the battery (manual shutoff switch at negative terminal), wait 30 seconds (I'm not sure why I'm doing this, maybe I read it somewhere? but it seems it can't hurt), then turn it back on. I can now start the car and run it. Until I turn it off. Then the process repeats.

Is some anti-theft something or other being triggered that then gets re-set when the battery is disconnected? Something else I should try?

*I believe there is ALSO a battery drain issue. But having read all the other threads I am now educated enough to at least start troubleshooting that once I get this sorted.

sound like you have a bad connection I would check the ground cable where it mounts to the body. your losing the battery you need to check battery cables

First and foremost change your DME relay in the main fuse box.

This seems to be a bad connection to the battery. I'd start with checking all cables and couplings from both poles to the related circuitry.
To find a current thief, here's a DIY check list and overview of the most common issues.
Cheers,
Tore

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The description of the problems does not match a faulty DME relay at all so no need to change that!

This does not make sense! DME relays don't drain batteries!

What is the voltage measured at the battery during one of these "no start" conditions?

hi, I’m having a very similar problem. What ended up being the solution for you?

964s are antiques.

I had internal corrosion on a positive side battery cable. The car wouldn’t start, the cable looked fine on the outside, but I replaced the cable because it was a 40 year old car (at the time) and I had never replaced it (it was a WAG, I couldn’t find any other problem). The new cable solved the problem, so I cut open the old cable (after replacing it) out of curiosity and found the corrosion.

On another antique, I had one of those green screw out cable disconnects internally corrode enough to maintain electrical power. I noticed the internal light come on when I opened the driver side door with the green disconnect in my hand as I was about to do some electrical work! Scared me a bit. Now I use knife switch disconnects on my old cars. I don’t like having power on a seldom used old car (I own three antiques).

I also replace rubber brake lines every five years or so after having one collapse on the inside. It looked fine on the outside, but locked up a caliper and I almost burned down the car. I do the same for old rubber gas lines after having a couple of fuel leaks. Nothing like the smell of raw fuel while driving to raise the hair on the back of your neck.

I was a functional check pilot in the Navy a million years ago, so I was trained to troubleshoot.

Thanks for the tips! I got my car to start-- it ended up being a short in the fuse box's harness. I need to look into the brake lines if that's the case. I already replaced all the fuel lines in the engine bay but now I found that a return fuel line is leaking just under the fuel tank.

It's so funny to me not too long ago I was working on older cars to make it to work and now I'm doing it again! It's definitely a lot more enjoyable this time around.

That’s good to know.

My corvette had its wire harness and fuse box replaced by the previous owner. It’s nice not having to rely on 60 year old insulation.