I HATE electrical problems!!!!

[jluetjen]

After I resolved the electrical problems from earlier this year I've been driving my 911 all summer, and it's run like a dream. It starts, it runs, it gets 24+ MPG. It's almost like having a modern car!

Then earlier this week the same old problem returned -- without warning the ignition goes dead. Neither the fuel pump nor the ignition system comes on when you turn the key (nor does the alternator light), turning the key to start doesn't do anything. It happened twice in close succession and restarted a few minutes later, so I was able to drive home. The next time I had the car out, the same thing happened, but it was a hard failure and I needed a tow home. At least I had my trouble-shooting tools in the car and I was able to confirm that...

-The battery was reading ~3.5 volts.
-When I turned the key, the same voltage went to fuse 6 (which is tied into the run circuit)
-I disconnected the battery and still got the same voltage.

Ahah! Maybe the battery has a dead cell or an internal short. I pulled the battery and picked up a new one at Autozone. When it came out of the car, the car was still dead as before, and the battery still said 3.5 volts. The guy at Autozone said that the battary looked good, but low on charge but since it was 6 years old I replaced it anyhow.

When I got home I plugged it in and...

... nothing. The same symptom persisted. When trying to start the car I noticed an audible spark sound when I turned the key, so I ordered another ignition switch from our host.

Two days later it arrived and I plugged it in -- and still nothing!!!
So I started unplugging all of the connections to the switch, and confirmed the connections with an ohm meter before reinstalled the whole thing in the car. Still no improvement. I also noticed that sometime when I turned the ignition on, I would read ~3.5 volts on the run circuit. Nothing seemed to make a difference.

So I pulled all of the fuses from the front fuse panels and the 3 relays behind the dash. Starting with just fuses 1 and 2, the fuel pump would come on the starter crank on command. Progress! So I added the fuses one at at time through the whole first panel, and things were still looking good. Next I added the fuses in the second fuse panel, and still the fuel pump would run and the starter crank as normal. Finally I re-added the 3 relays, and still everything worked. So I took the car out for a spin around the block, turned on the headlights, used both directionals, ran the washer pump and the wipers, started the blower fan and pushed in the cigarette lighter. Everything worked!!!

What did I do???

AAAAaaahhhhhhhhhh!!!!!!

[Cdnone1]

I don't think you have solved your problem. I would bet you have a short to ground somewhere that will rear it's ugly head again
Sorry
Steve

[Joe Bob]

Probably knocked some corrosion off a fuse or seated a relay that was a bit kerflumpf...sorry to use a technical term.....

Mine died last week.....found the fuse. licked it and it worked. Tasted awful.

[Brando]

Jluetjen, it may be time to upgrade to the modern blade fuses.

It also wouldn't hurt to (disconnect the battery and) pull every fuse, unscrew the contacts and clean them, then re-insert them to the fuse-panel and tighten it back up. Time to check your grounds and clean them. Put a little dielectric snot on them afterwards.

Corrosion can cause all sorts of problems.

Also, it wouldn't hurt to crawl under the car and take a gander at the wires attached to the starter.

[911pcars]

John,
Assuming the battery is good and connected correctly:

The voltage source for the ignition switch (and thus starting and ignition) is from no. 1 fuse position (as is my '69). I'm sure you've checked the fuse and it's okay. However, the post connector-to-wire contact at the fuse box could be the issue. Try loosening then tightening the screw terminals on this fuse, then retry.

If a no-go. connect a multimeter at the ignition switch (#30) to measure source voltage. None as per symptoms? Probe towards the fuse panel to see where the source path is interrupted.

If voltage is good at #30 position, switch the ignition ON, then check source voltage at terminal #50 when the switch is in the "start" position. This energizes the starter solenoid and should be about 9-10 volts during cranking.

Let us know.

Sherwood

[Bobboloo]

The fuse blocks can develop corrosion on the back side. I would suggest disconnecting the battery and then removing the fuse blocks to inspect the backside.

You might consider taking some flux to the copper bridges on the back and adding some solder. The posts are just riveted to the bridges and corrosion gets in there.

[jluetjen]

Originally Posted by Brando

Jluetjen, it may be time to upgrade to the modern blade fuses.

It also wouldn't hurt to (disconnect the battery and) pull every fuse, unscrew the contacts and clean them, then re-insert them to the fuse-panel and tighten it back up. Time to check your grounds and clean them. Put a little dielectric snot on them afterwards.

Corrosion can cause all sorts of problems.

Also, it wouldn't hurt to crawl under the car and take a gander at the wires attached to the starter.

Good points all. The wires to the starter are in fine condition an clean. I just checked them in the spring time.

The voltage source for the ignition switch (and thus starting and ignition) is from no. 1 fuse position (as is my '69). I'm sure you've checked the fuse and it's okay. However, the post connector-to-wire contact at the fuse box could be the issue. Try loosening then tightening the screw terminals on this fuse, then retry.

If a no-go. connect a multimeter at the ignition switch (#30) to measure source voltage. None as per symptoms? Probe towards the fuse panel to see where the source path is interrupted.

If voltage is good at #30 position, switch the ignition ON, then check source voltage at terminal #50 when the switch is in the "start" position. This energizes the starter solenoid and should be about 9-10 volts during cranking.

Let us know.

Good point. Earlier in the week when the car died, I was measuring ~3 volts at fuse one as long as the car wasn't starting. I checked each fuse yesterday when I pulled them out and they were fine. I also measured the same voltage into and out of the switch, and on the yellow wire (start circuit) when the key was turned to "start". The problem is probably between the battery and the start switch since it is affecting both start and run. Headlights, wires and stuff like that continue to work unaffected.

As a side note...
The previous owner had added a cable from the battery directly to the starter so that it is in parallel rather than in series with the rest of the car. I don't see that as a problem.

As a result of my electrical fire, and what the PO did with the starter the wiring has been changed slighty. Unlike what is shown in the wiring schematic I've moved the battery connections fuse locations 1 and 2 to the opposite side and added a 25 amp fuse, so all of the circuits connected to fuses 1-5 are now downstream from a 25 amp fuse. In the factory schematic all of these circuits are unfused.

I think that I'll confirm that all of the fuse terminals are clean next.

[jluetjen]

Ahha!!!

I pulled the 911 out of the garage this afternoon and it started right up. So I turned it off and pulled out fuses 1 and 2. When I tried to restart, nothing happened. Everything was as before with the exception of headlights, which wouldn't operate.

So I put fuse 1 back in and now the headlights work*, but the engine doesn't crank or start. The charging light doesn't come on either. It looks just like the problem that I've been having. So I guess I'll polish off the contacts for that fuse and see how it goes.

Here's hoping!!!




* The previous owner had wired the headlights with relays as opposed to having the current go through the switch. So that's another change to the electrical diagram. It's worked for almost 10 years now so I've never messed with them.

[Cdnone1]

Have a look at this.
I am having the exact same problem. This didn't solve it but it didn't hurt. I have had the switch out and replaced, the 14 pin connector a parts and cleaned and am still chasing an intermittent start problem.
Good luck and keep us posted, especially if you find the solution
can this be cleaned up?

Steve

[RWebb]

John - you know about using vinegar to remove the corrosion on the fuse and its socket, right?

I always spray it with Caig ProGold after I clean it.

[jluetjen]

Actually Randy I scraped the leads with a screw driver, and then I borrowed from tarnex from my wife. We'll see how that works.