No Start '74 CIS... Electrical Gremlins...

[Don Z.]

This is just strange.

Turn the key. Engine turns over, does not fire. Turn the key again. Solenoid clicks, then all electrics shut off.

At first, I thought it was the switch itself shorting out, so I replaced that. Fully charged the battery.

First turn. Put the key to "run". Solid whine from the CD box. Radio works. Headlights on, then back off to start. Turn to start: Solenoid click, no more radio, no more CD.

Wait five minutes. Trunk light still on (noticed that when I hooked up the battery charger again. But no electrics anywhere. Five minutes later, the headlights still don't work, but I can flash brights... turn the headlights on, no light... but the fuel guage swings past full. Turn the lights off. Turn key on. Fuel gauge goes to three quarter (that seems right for the actual level). Turn to start... engine spins for about five seconds, does not fire. Rather than just spin it for thirty or forty seconds, I let go of the key... turn to off, back on. CD Box whine. Try to start it again, click... no more electrics.

Repeat cycle every ten minutes or so for an hour.

Swear in both English and German... Still can't get the thing to go. Starter? Solenoid? Loose ground someplace? No idea, but very frustrated...

Suggestions?

[Fidalgo911S]

That is odd. I'd check all grounds, clean battery terminals, disconnect battery and check/clean solenoid connections. Then try again.

I'm no electrical genius so that's the extent of my knowledge.

[Don Z.]

Monday morning bump... Any ideas, guys? I have no idea where to even begin to look...

[Don Z.]

Would a short in the battery make sense?

[Early_S_Man]

Don,

Losing power from an ignition switch is not necessarily a 'short' ... more often it is an intermittent 'open' condition!

However, from your starting sequence description ... it sounds like your battery may only have a 'surface' charge, and after one cranking attempt, battery Voltage is too low to operate radio, CDI, headlamps etc. Hence the ten minute cycle of 'lost' power. The capability shown by your battery is not that of a fully-charged battery by any means! I strongly suggest that you need to charge your battery with a 6 - 10 Amp charger, overnight, or longer!

The electrical portion of the ignition switch may be faulty. It can be replaced as a separate part. Not really the suspect at this point by my judgement at this point, though.

964-613-012-00-M100 Ignition Switch - Electrical Portion only, 911 (1974-89) Brand: Genuine Porsche $58.75

You can, of course, verify that different circuits are losing power when the switch is operated ... with a multimeter and long test leads. This needs to be done after the battery is fully charged, of course!

BTW, it is normal for radio and lights to be switched off when ignition switch is in the 'Start' position vs the 'Run' or 'On' position.

[Porsche_monkey]

Originally posted by Early_S_Man

The electrical portion of the ignition switch may be faulty. It can be replaced as a separate part. Not really the suspect at this point by my judgement at this point, though.

964-613-012-00-M100 Ignition Switch - Electrical Portion only, 911 (1974-89) Brand: Genuine Porsche $58.75

That was my guess. Very common on the older cars for this to crap out.

[Don Z.]

Thank you. Actually, the first thing I did was replace the switch. So that's done. "Surface charge" makes sense, which is what I was thinking. I wanted to take the battery out and to a load test, but did not have time this weekend.

Understood the radio goes off at the start position. But it should go back on when you put it back to start, which it was not doing. The CD box should whine at "run", and continue to whine whether at "run" or "start". In this case, the solenoid would click, and then the only electrical thing that worked was the under hood light, and that's it. To be clear, I'd turn the key to run, hear the whine... turn it to start, and then click... nothing. My thoughts were lack of power, dying starter, or a loose ground that I wouldn't even begin to know where to start looking...

So I'll load test the battery. I did charge it with a 20 amp charger, but that was only for an hour. Lower amps over more time makes sense, but you know how it is... you put the new switch in, and you want to see if it works "right now".

But at least I know I'm going in the right direction, even if I'm not actually getting anywhere!

[Porsche_monkey]

Don't load test it, just connect a voltmeter or test light to it and see what your voltage drops to when you try to crank.