Electrical Issues - Solved and lessons learned.
 

I have an 88. I've done a lot of work to it. Twice in a row now I had some stubborn electrical issues that had the same solution

Problem one was the heater blower. It stopped working. Confusing system as it is I was able to narrow it down. The blower motor would work when you jumped 12V to it. When I used a multimeter on the connector it showed 12V as well....WTF? How can that be? I only figured it out when I read the voltage on the connector when the blower was plugged in. 0V. The circuit had too much resistance in it to deliver any significant amperage. The problem: Corrosion on the fuse.. You couldn't see any problem with the fuse just looking at it, you had to take it out and look at the ends. A bit of sand paper later and it was good to go. For me advice/instruction 'check your fuses' had always meant a visual check, nothing more. Especially if the mulitmeter showed 12V

Problem two was the head light washer system. Jump 12V to the motor and it works. Press the switch (with headlights on) and you hear a click. Look at the fuse and it's not burned out. Again, it was only after I took the fuse out and cleaned the ends that it the thing started to work.

I have since cleaned every fuse, including the ones in the engine compartment. I can only imagine what other problems they were causing by having too much resistance in the circuit. I am also curious if it affected the motronic system.

I hope this saves someone some headaches.

PS, on the carrera it is possible to access the headlight washer pump with out taking the bumper off. You just have to take the bellow off and have small girlish hands or access to small girl who has hands.

I've recently been tracking down numerous electrical issues in my '72 911T. Cleaning up the fuse box solved several problems for me. Fellow Pelicans pointed out that the multiple ground points (under the hood, behind the dash, outside the battery boxes, and in the engine compartment) can corrode and cause many electrical problems. Cleaning these helped a lot.

I lived near the beach and once every few months would spin the fuses to break the chemical bond. Ended up wearing out the ends.

Fixed that with an upgrade fuse box with bladed fuses.

I wanted to avoid similar problems. This was the hot ticket for me, in both of my cars and friends cars. Great stuff!

Classic Retrofit Fuse Pannel

Yea, BTDT. However, it is not just the fuses. Many of the other connectors and grounds can do the same thing.

What I did is use a digital volt meter with one probe on one side of the connection or fuse and the other probe on the other side of the connection. No voltage should be read with the power on.

I was reading .5volts around my fuses. So there was resistance.

Yes, a good thing to remember about our fuses... I once left my car with a valet who let the engine die. Couldn't re-start it. I had an appointment with a ribeye and Cabernet, so we pushed it into a spot, and I re-appeared a few hours later. Went straight to the fuse panel, rolled them a bit, car fired right up!

Once upon a time my car died on my way to work. No whine from the CDI. I LOOKED at the fuses, the seemed fine.

Later, after being towed home, I noticed the ignition fuse was burned on the END of the fuse.:mad:

Igntion fuse? Unless you have added this, the CDI box is not fused on any 911 with standard wiring.

The 'continental' bullet fuses are an issue on many European cars. If you want to stick with them I'd suggest you make sure they are the proper ceramic type (not plastic) which are increasingly difficult to find. The plastic ones can melt.

You'd be surprised how many people think the electrics are bad on a 911 when really it is just the fuses. E.g. electric windows and sunroof are noticeably faster when converting to blades. If you go with our replacemnt system you'll find the headlamps around 20% brighter too!

i have been telling people on here to use a test light instead of a MM for electrical work for years now because of the very issue of resistance reducing current but you canstill measure 12v. in fact, even had a few arguments about it with the other side stating "YOU MUST KNOW THE VOLATAGE!!"
I have even seen your problem repeated here. tail lights is a common place for this error. "I measure 12v at the light socket but the light does not work so I spent $$$ guessing at what it could be:"

sorry to rant but...

a MM does not need current to measure 12v. a light bulb requires current to light it, thus the need to use a test light instead.

old man neri and sballard...
Really dumb question: how do you clean the fuse connections and the ground points? Also, how does one clean the contacts for the round multi-pin relays?
Thanks in advance for any info/direction....

Not a dumb question.

Step one: disconnect the battery. You never know what is hot and you don't want to short something.

For the fuses I just use light sand paper and some spray on contact cleaner. They are delicate so one must be gentle on them.

The ground points are usually more robust. Clean the contact surfaces in a similar manner as above until shiny and clean.

Pins and pin receptacles are probably the trickiest and most delicate. Some people have had good luck using erasers on the pins. The receptacles I just spray contact cleaner in there and hope for the best. In my experience the pins and receptacles suffer least from this problems as the are the least exposed. I'm sure someone else has a better way to clean them.

also remove the wires from the fuse block and clean the screw and wire ends.

Thanks Guys...Happy Motoring!

Another valuable trick I learned from timmy2. Sometimes the posts on the round relays get loose. If you look at the posts straight on you will see that they are slotted. Use a razor blade to spread the posts to make better contact.

The wire brush attachment on Dremel tools is pretty handy for removing corrosion.

Also I recommend using Deoxit D5 as a contact cleaner. Stuff works great!

Excellent suggestions...thanks very much

Yes this fixed an intermittent power windows not working issue for me.

Did I see someone mention previously that a .22 cal bore brush works well to clean the holes into which the wires are inserted? My fuse panel has a fair amount of light corrosion and I think I am going to clean it up today. Several of the fuses have some corrosion and look over 20 years old so I think I will probably just replace all the fuses with new ones. I plan to use a Dremel with wire brush to clean the contacts.

Should I use something to clean the exposed ends of the wires before re-inserting them into the fuse panel? A chemical? Or just use the wire brush for that too?

Previous post on using a test light instead of a DVM is an excellent suggestion. Just found this out troubleshooting a problem with my AC system. DVM showed 10+ volts but test light was extremely faint.

Finished a little fuse pane rehab. Used some of the recommended Deoxit D5 and it seemed to work fine. I wasn’t having electrical issues so I didn’t need to fix anything. I only had a couple holes that had corrosion and a .223 bore brush worked fine for that. I used my Dremel with some brass brushes to clean the corrosion off the contacts. Worked very well. Replaced all the fuses. Some of the old ones were corroded in place and basically broke apart when I attempted to remove them. For some reason my fuel pump fuse was a 16A instead of the prescribed 25A. Any idea why that might be? I assume someone didn’t have the correct fuse or just didn’t know. After all was finished I checked all the electrical functionality and everything worked as expected. That’s one fewer thing I need to worry about. Looking forward to removing the old Clifford alarm and the rat’s nest of wiring that goes with it!