Updated rear fuse panel

[jazzbass]

There are things I love about my car - the mechanical engineering is amazing. And there are things I hate about my car - the electrical system absolutely drives me insane. Circuits that aren't fused, full headlight current run through the turn signal switch, bad grounds, and fuse boxes designed in 1940.

So I'm in Pep Boys today buying some 30W oil for the lawn mower, and I see this for $4:



Not the bandsaw, but the ATO/ATC fuse block. 4 fuses, 80A. The new block actually has mounting tabs which have been cut off in this picture (hence the bandsaw).

On my way home, I start planning - thinking about how I could design a new front fuse box with several of these blocks. They snap together, and I'd fab a new holder for them.... then I get home and look at my 911 in, roughly, 100 different peices in my garage. I'm in the middle of a suspension overhall, and just for giggles, I'm replacing the interior at the same time. Oh, and installing H4s and a new windshield, too.

So designing, building and installing a new front fuse box gets shelved. But I have this fuse block - what to do? That's right, replace the engine compartment fuse block. So I start with this:



I hate those fuses - really. So I pull the whole assembly, remove the relays and the old fuse block. Now, time to install the new one, hopefully in a way that makes it look the way Porsche should have done it around 1979.

Step 1 - Mark the chassis to cut out a hole for the new fuse block.


Step 2- Cut it out with a jig saw and lots of filing. It's aluminum, so it cuts and files nice and easy like.


Step 3 - Fab up some brakets to hold the new block. These are made from 1/8" angle aluminum I got from Home Depot for $5. TO make it so the fuse block could slide in and out easily (since the block will be wired directly into the car), I used #6 countersunk machine screws to attach the brackets to the chassis.


Step 4 - Install the block. I used 2 #6 machine screws in the side of the fuse block to bolt it to the chassis.


And its done!


It was really pretty easy - the whole process took about an hour (not counting trips to Pep Boys and Home Depot). I'll install it tomorrow, and since there's only 5 wires, that should take another 1/2 hour or so. Three down, 21 more to go!

[masraum]

Very cool!! And I nice looking job of it too.

[masraum]

Hmm, well, the picture seems to be gone, but someone has already done exactly this for the front box, here's the thread, maybe Olivier will repost the pic for us. I think this thread may have part numbers or something too.

http://forums.pelicanparts.com/showthread.php?threadid=100263

[jazzbass]

Originally posted by masraum
Hmm, well, the picture seems to be gone, but someone has already done exactly this for the front box, here's the thread, maybe Olivier will repost the pic for us. I think this thread may have part numbers or something too.

http://forums.pelicanparts.com/showthread.php?threadid=100263

I remember when I had my 73 VW I wanted to rewire the fuse box because I had NOTHING but problems with it. Imagine my joy 10 years later at discovering the mid-Eighties car I bought also had the same stupid fuses! The thread you list here is the one that really got the idea going, though. It was a nice looking job - I wonder where the picture went.

[DavidI]

Great looking job! I may do the same after seeing the clean look.

David

[vash]

great job. i saw a block at my autoparts store that used the glass tube type fuses. iwas going to use that. there is one for 3 fuses already. your original one is way cleaner than mine already!

[aigel]

I thought there was a cover to keep your eyes off the WW2 electrics. I sure was shocked to see those fuses, when I got the car. There is no excuse, they just never redesigned it because they wanted to make max. profit. I would have really been pissed, paying 38k in 1981 for a car with such an electrical system. If you buy it 22 years old, it is worth a good laugh.

Great job, make it a kit and sell it to us!

George

[Glasgow 911SC]

I updated my rear fuse panel too as the fuses were forever corrodong. It seems impossible to find a block for 3 blade fuses however, so I bought 3 individual ones that snap together.

I reassembled and it worked fine for a while. The heated rear screen fuse must hve a short somewhere in the circuit though, because I've melted the fuse and holder!

Chris,
how are you going to jumper the connectors together? On mine the top 2 old fuses fed off the same power source and were jumpered by a copper strip. I cant seem to find a suitable, blade fuse, alternative.

[Randy Webb]

Ronin would be prous of you ....


Pelican ought to make a fuse block upgrade kit for these cars -- especially the 1973! It would be a big seller.

Listening, Wayne?

[Bigtoe]

NICE JOB!

Sanitary installation and space for a spare fuse!
Who wouldn't spend a hour for such great results?

[fred cook]

Ah, the never ending tale of "fuse woes" in a 911. I did the flat fuse conversion on my SC a little over a year ago. Since then, no blown fuses and no electrical problems! Here is a picture of the rebuilt fuse box in my '80 SC coupe.



The fuse holders came from Norway (Thanks Ove) and are rated for fuses up to 20 amps. The only existing circuit that exceeded the 20 amp limit is the fuse that supplies power for the front condenser fan AND the evaporator fan. Since there was room for 24 of the new fuses (vs 21 originals) I simply put the two fans on separate fuses. By mounting the fuse holders in an aluminum bracket that I made, the original fuse cover will still fit. You will probably have to extend a couple of wires and be sure to use the very best connectors that you can find. On the connectors that are attached to major power leads, I soldered and crimped to make certain of a good connection.

Good Luck!
Fred Cook
'80 911SC coupe

[jazzbass]

That looks great, Fred. That's my goal after the suspension and interior are back in.

[Par911]

Nice Job Chris. Too bad I couldn't make it over to help you tear her apart some more.

[Par911]

What's the deal with all the black relays?

What's the difference between them and the red ones?

[jazzbass]

Originally posted by Par911
What's the difference between them and the red ones?

There is a diode across the relay contacts on the red ones. These are used when the relay controls any type of inductive load, like a motor. Inductors don't like to turn off, and when they do, generate a spike of electricity in the opposite direction. The diode suppresses that spike by shorting it to ground instead of letting it arc and burn out the relay contacts.

[Bigtoe]

Chris,

Excellent explanation!
I checked your profile and was bummed that it didn't show you as an Electrical Engineer.

[fred cook]

The picture that I posted is for the front, main fuse box. The red relay is the fuel pump relay. The black ones are for everything else. Sorry about the confusion. I did however replace the rear 3 panel fuse block with 4 of the same type flat fuse holders. I also added a 4th fuse, but in my case it is for the main power input into an MSD ignition box. Now my SC is totaly free of the old, original stick type fuses.

Fred Cook
'80 911SC coupe

[vesnyder]

Great job. I have not had much issue with the old style fuses, but if I do I now know the solution!

[david914]

I got a little reminder this afternoon on the way home of how fragile the old "torpedo" style fuses are. Near 90 degrees today, A/C on full tilt, and 1/3 the way home it dies. Of course, I knew exactly what it was. Pulled over, popped the hood, and removed the fuse panel cover. Um-hmm, just as I suspected, A/C fuse burnt to bloody hell. Fortunately, I carry plenty of spares (a by-product of cutting my teeth on old VW's) and replaced the fuse. Ahhh, that's more like it, only 85 degrees inside the cockpit now instead of 90. Much better!

Fred, have you (or did you) ever documented your fuse box "upgrade"? It looks very clean! I'm sure most of us would like to see more details on how you made the bracket to hold the new fuse holders and where you got the fuse holders from. I know I would!

[Early_S_Man]

Uh ... Chris, the diode in the red relays, and the resistor or diode in standard DIN relays ... is across the coil, not the contacts!!! Suppression diodes, as they are commonly referred to, have nothing to do with contact arcing ... they are to suppress the high-Voltage inductive spike that would normally be introduced to the +12 Volt power bus and cause havok to semiconductor devices spread thoughout the electrical system, such as CDI units, factory alarm control boxes, etc!

Back to fuse boxes, etc. ...

If the fuse blocks are cleaned annually ... polishing/rubbing compound on the fuses to burnish corrosion, followed by cleaning with Q-tips and Brakleen, then a coating of Dow Corning 4, 4X, 111, or 112 Silicone Grease ... you won't have any problems with the OEM fuses or blocks!!!

ATC fuses and blocks aren't immune to problems in 20-year old cars, either, though the fuse selection is much, much better! I have seen '80s cars with partially-melted ATC fuse blocks ... and if you want to talk about a real nightmare ... just try doing repairs to a USA-made auto fuse block and wiring harness after being overheated!!! ATC fuses do have more contact area than the OEM German fuses, but you are still only talking about the same equivalent connection as a single 0.25" Faston connector at each side of the fuse ... hardly ideal for high-Amperage circuits of 25 A or more! For those, you should really use the Maxi-fuses which are the equivalent of 0.375" Fastons on each side!

Last week I posted a message about a modular ATC fuse block, but I mistakenly referred to Littlefuse as the mfr, when it should have been Bussmann ... the 15660-series on p. 17 of the following catalog is what I was referring to ...

http://www.bussauto.com/shared/library/catalogs/Buss_Auto-Fuse_Cat.pdf