Welcome all 928 forum refugees!
User avatar
By Shifted
#38013
Here's mine:
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The cable is flat enough to be placed in the same location as the factory flat grounding strap. It would also be very easy to wire in a whole car fuse. If you wanted quicker access to the switch, you could put a hole in the tool panel to be able to access the switch without removing the panel.

These are the components:

1x Battery terminal for 2 AWG wire:
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30" of 2 gauge flat marine cable:
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2x 3/8" 2 gauge ring terminals
1x 5/16" 2 gauge ring terminal
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1 to 4 5/16" washers:
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1x Battery Switch On/Off (275 Amp continuous, 455 Amp intermittent, 1250 Amp momentary):
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3/4" Dual wall adhesive heat shrink tubing:
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And how I assembled it:

1) Cut a length of wire so that with a 3/8" ring terminal on one end and the battery terminal on the other end, it will place the center of the battery terminal hole 21" from the body of the switch. You'll need to mock everything up and lay it out so that you can see exactly where the terminals will line up.

2) Do the same as above for the second wire, but with one end a 3/8" ring terminal and the other a 5/16" ring terminal. From the body of the switch to the center of the hole for the 5/16" ring terminal it should be 8-5/8".

3) Slide heat shrink tubing onto both ends of both wires. Strip the ends of the two wires. Crimp the battery terminal and 3/8" ring terminal to the longer wire, and the 3/8" and 5/16" ring terminals to the shorter wire. Pay attention to how the terminals are oriented with respect to the flat part of the wire. You'll want to make it easy to lay the flat wire along the lip of the battery tray opening and minimize the amount of twisting that you have to do in order to mount everything.

4) Heat up the heat shrink until you see the adhesive begin to squeeze out of the ends.

5) Bolt the 3/8" ring terminals to the terminals in the switch. After you assemble the switch, you will probably need to cut off the assembly bolts because they are usually pretty long.

6) Remove the factory ground strap. Make sure that the switch is in the off position and thread the wires into position. Attach the battery terminal to the negative post on the battery, and the 5/16" ring terminal to the grounding point that the factory ground strap was connected to. You may need to use 5/16" washers to space the wing nut high enough that it clears the new cable and terminal end.


For tools, a utility knife with a fresh razor blade works very well for scoring the sheathing on the wire. Good quality dikes work well for cutting the wire itself. Scissors are good for cutting the heat shrink, but the utility knife or dikes can work as well. A butane combination torch with the soldering tip removed works well for the heat shrink, but so does a heat gun, hair dryer or even a propane burner or butane lighter.

For crimping, you can definitely get away with a hammer crimper. But, a hydraulic crimper with hexagonal dies is best and easiest. You can also use solder slugs, if that's your preference.
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User avatar
By Sazerac
#39042
Well, there's an idea.

I used some of those switches that are mounted directly on the terminals and they kept corroding and causing electrical problems. On all my cars, I just pull the cable now. The switch you have looks robust. Do you have a link to it?
User avatar
By Shifted
#39043
The particular one that I ordered is no longer available on Amazon. But, it's generic and sold under lots of names, probably due to community/open-source manufacturing. Here it is under a different brand:

https://www.amazon.com/Nilight-Waterpro ... 07T288VN8/

It's a pretty standard design, so you can find much higher quality switches in the same size and with the same sized lugs. You can even find ones with removable "keys" so you could potentially mount the switch through the tool panel and then remove the "key" so that it doesn't get bumped accidentally.
User avatar
By linderpat
#39329
Shifted wrote: Sat Nov 28, 2020 9:07 pm Here's mine:

image.png

I like that. I may do this. :rockon:
User avatar
By Geza-aka-Zombo
#39392
Nice installation! I used this one - made a small right angle bracket to mount it. After reading that post about the 928 that went up in flames at ~2:00 am in a shop, mine get's shut off every time.

https://www.amazon.com/Fastronix-Curren ... 469&sr=8-5

Image
User avatar
By Shifted
#39395
With a remote cut off switch, it would be really easy to wire in a whole car fuse.

I remember reading that thread thoroughly, and looking at all of the photos. To be honest, I don't think the cause was as innocent and universally applicable as the business owner made it out to be. My personal opinion is that it was due to negligence of the shop, not anything inherently wrong with the 928's design, vehicle age included. How many others like this have you heard of vis-a-vis failed fuel line fires?

Regardless, my primary use for the cut off switch is to make it easy to work on things requiring the power to be disconnected. And it is really really useful for that.
User avatar
By Hey_Allen
#39448
Shifted wrote: Fri Dec 04, 2020 7:48 am With a remote cut off switch, it would be really easy to wire in a whole car fuse.

... not anything inherently wrong with the 928's design, vehicle age included.
After the picture thread about the fire, I found a large fuse holder with intent to install it on my car.

That said, I have found degraded wiring on my car, with insulation just dissolving or cracked and crumbling off, so I'm not going to totaly lay the blame on the shop.
User avatar
By Shifted
#39452
I understand and respect that. When that thread was active, I pointed out that ANL fuses are the right type for this application and provided technical references to back it up, but Carl ignored it and stuck with the MEGA/AMG fuses. Just something to consider before you commit to a fuse type.
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User avatar
By worf
#39630
Shifted wrote: Fri Dec 04, 2020 7:48 am I remember reading that thread thoroughly, and looking at all of the photos. To be honest, I don't think the cause was as innocent and universally applicable as the business owner made it out to be. My personal opinion is that it was due to negligence of the shop, not anything inherently wrong with the 928's design, vehicle age included.
I posted to that thread with some observations of how the front main harness is often misrouted.

Also, 'round the same time I had just installed a brand-new-out-of-the-Porsche-bag engine bay (light) harness. The NOS is remarkably cheap for what it is. Reminds me that I need to pickup a spare for my '91 while they're available.

In any case, with everything correctly routed, in my opinion, a car fire caused by the light harness or front-main harness is effectively impossible.

My bet is that that car, earlier in it's life suffered collision damage in/around that area and the harness was either damaged and not replaced, or damage wasn't noticed, or was improperly routed/installed during the work.

I have seen with my own eyes, too many times, how body shops 'skip' things or just plan fuck things up.
Hey_Allen wrote: Fri Dec 04, 2020 11:54 am That said, I have found degraded wiring on my car, with insulation just dissolving or cracked and crumbling off, so I'm not going to totaly lay the blame on the shop.
This too. I have noticed over the last 5-ish years that all of the wiring harness on 928s brought to me are very brittle. I take extreme care to perturb them only as much as needed and every single time I see cracked insulation on a power lead I deal with it.

Now, as far as insulation just 'disintegrating' on 12v leads, this I have yet to see except for the front main harness. That harness gets the most 'abuse.'

The jump post area and ABS terminal area always get an inspection on a new-to-me 928.
Shifted wrote: Fri Dec 04, 2020 7:48 am How many others like this have you heard of vis-a-vis failed fuel line fires?
I am of the opinion that the majority of fuel fires are the result of poor work(*) just prior to the fire. Or, in other words, 100% of fuel fires after fuel system related work are the result of poor work. I believe that there have been fuel fires due to three-decade old fuel lines releasing fuel however, I do not recall a credible story being posted to the other site.

I, once, a long time ago, received an S4 on a flat bed. Long story short, after some repair work, not fuel related, I took it on a test drive for evaluation. One result of that evaluation was an intake refresh. When I went to remove the intake as I was wiggling it up, I started smelling fresh fuel. After investigating I discovered that the return line from the regulator had a crack in it such that every time the motor rocked side-to-side a drop of fuel would escape.

A couple of things I learned from this:
- check your fuel lines often once they are 10 years old
- a drip of fuel isn't an instant engine fire
- when you do motor mounts be damned sure your supply and return fuel lines are in really good shape
- if for some reason you get a 'new' 928 into your possession, always inspect the fuel lines. And I mean the part of them you can't see. With an inspection mirror. And wiggle them.

(*) Poor work seems, IMO, to be lacking in one or both of these:

1) Always, always, always, do a long careful leak check by bypassing the FP relay as soon as you 'button up' the fuel system.

2) Fuel injectors go into the rails, then the rails go into the engine. Never, ever, ever the reverse.
User avatar
By hessank
#39674
Shifted wrote: Fri Dec 04, 2020 12:04 pm .............. I pointed out that ANL fuses are the right type for this application and provided technical references to back it up, ......... Just something to consider before you commit to a fuse type.
Can you please expand what you mean without going too technical?
While my car is sleeping and the battery is removed I plan on installing one of these System Protection Fuse.
Also can you say what amperage and is it installed on the Positive or Negative cable?
Please and thanks
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User avatar
By Crumpler
#39681
Shifted wrote: Fri Dec 04, 2020 7:48 am With a remote cut off switch, it would be really easy to wire in a whole car fuse.

I remember reading that thread thoroughly, and looking at all of the photos. To be honest, I don't think the cause was as innocent and universally applicable as the business owner made it out to be. My personal opinion is that it was due to negligence of the shop, not anything inherently wrong with the 928's design, vehicle age included.
Yep.
And yet with every tragedy there is a budding business opportunity!
When I followed that thread I was mouth agape to see that the shop owner then marketed a kit to not burn down a car in your shop....that took brass tacks.
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User avatar
By Shifted
#39707
Crumpler, you're right on the money with that one. Pun intended.

With respect to ANL versus MEGA, one of the main reasons that ANL is preferred is due to the interrupt rating. When a MEGA fuse blows, the melted metal can still congeal an allow the circuit to continue to be completed if the amperage is high enough. ANL fuses are designed to prevent that and have specific interrupt ratings.

Here are a couple of places that give some additional information in very simple terms:

https://www.vteworld.com/resource/html/ ... ga_anl.php

https://shop.pkys.com/A-comparison-of-A ... _b_44.html

There are more technical references available that you can probably find online just as easily as me, but that's the short of it. ANL fuses are designed for, among other things, cable protection and the very high amperage that can occur with a battery shorted to ground through a cable. MEGA fuses, on the other hand, are designed to protect electric motors and loads that draw too much current, not for guarding against a cable shorting to ground with a high amperage battery connected.
User avatar
By Shifted
#39843
I forgot to add that it doesn't matter if it's on the negative or positive, as long as it completely interrupts all paths that might complete a circuit to the battery. Traditionally, it's done on the positive wire, but putting it on the ground strap is fine. As for the amperage rating, I don't know specifically what is needed. It would need to be enough to let the starter crank when hot, which is more current than cranking when cold.

If you don't have any way of determining the amperage requirements, let me know and I can put am ammeter on mine and tell you what it says.
User avatar
By Erik N
#42001
How much?
User avatar
By Shifted
#42036
The cost of the materials for those last two was $30.77. But, the wire that I used has to be bought in 20' increments for about $57 including shipping.
User avatar
By SeanR
#42047
I'll be odd man out here. I abhor those things and have removed a ton of them from cars. Got a battery drain? Fix it. Want to disconnect the battery? Take the 13mm bolt or wing nut off and put a rag/cardboard on the end of the neg cable.

My '88 can sit there for a couple of months and will still crank over fine.
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User avatar
By Fox_
#42072
SeanR wrote: Mon Dec 14, 2020 5:54 pm I'll be odd man out here. I abhor those things and have removed a ton of them from cars. Got a battery drain? Fix it. Want to disconnect the battery? Take the 13mm bolt or wing nut off and put a rag/cardboard on the end of the neg cable.

My '88 can sit there for a couple of months and will still crank over fine.
Do they cause issues?

Would think a switch would be better than wearing out the threads in the ground post and/or accidentally arcing off the rear wiper motor housing. :hiding:
User avatar
By SeanR
#42074
In theory they shouldn't. But you are adding additional points to ground out your battery and a switch that can fail. Some of the mikey mouse stuff I have seen just makes me cringe when I see one. Seriously, if you want to store your car, undo a fucking bolt, not add a couple feet of wire and a switch that if you hit a bump is going to shut off going down the road.
User avatar
By Shifted
#42085
I hear you. Normally, I don't want extras like this on my cars. However, when I was doing my turbo build, the ability to very quickly disconnect the power was invaluable. For me, it's been a big positive with no down sides. And extremely easy to reverse. The only weak link is the switch itself. Which is very easy to replace or bypass. The cables and terminals are all high quality.
User avatar
By Shifted
#42086
Whoa...bad day? lol

It's not going to fail from bumps. It's not going to short or ground out. Nothing is exposed, and the wire quality far exceeds the OEM ground strap. The switch will eventually wear out. In a decade or three. And when/if it does, it's very easy to bypass or replace.

To each their own, but I wouldn't rag on someone else doing something that works for them.
User avatar
By SeanR
#42107
Shifted wrote: Mon Dec 14, 2020 7:32 pm Whoa...bad day? lol

It's not going to fail from bumps. It's not going to short or ground out. Nothing is exposed, and the wire quality far exceeds the OEM ground strap. The switch will eventually wear out. In a decade or three. And when/if it does, it's very easy to bypass or replace.

To each their own, but I wouldn't rag on someone else doing something that works for them.

Not a bad day at all. Unless you find some idiot put engine coolant in the windshield washer tank and had just fitted a new pump, which put that crap all over the car. Or had to fix someones idiot fix of a washer and a bunch of bolts to make a window roller work instead of doing the smart thing.

I was going to post exactly what I posted before but refrained because I figured it might hurt someone's feelings. Just decided to post my thoughts, of which I've had the same ones for years. You'll be fine and what you are doing looks great if someone were to want to go down that road. I still say one bolt and you are done.
User avatar
By linderpat
#42147
SeanR wrote: Mon Dec 14, 2020 5:54 pm I'll be odd man out here. I abhor those things and have removed a ton of them from cars. Got a battery drain? Fix it. Want to disconnect the battery? Take the 13mm bolt or wing nut off and put a rag/cardboard on the end of the neg cable.

My '88 can sit there for a couple of months and will still crank over fine.
I agree completely with this. I had a cut off on my Boxster because you cannot disconnect easily like the 928. I like the options here, but only for my 997, for the same reason as the Boxster.
User avatar
By Shifted
#42177
The problem with the 928 ground strap is that it's not like a normal car battery to disconnect. You can't just loosen a clamping bolt and then slip the terminal on and off of the battery, with a single motion creating/breaking a solid connection. You have to reach around and work a wing bolt, all while the strap is making intermittent connection. Sparking, setting the alarm's horn on and off, giving low/intermittent voltage to the electronics, and requiring a dexterous touch to get the bolt started.

When I work on someone else's car and just needed to disconnect the ground for one thing or one long session (like removing the alternator or disconnecting the ECU's), then I agree that it's no big deal to just unbolt the grounding strap. However, when you're doing a lot with the electrics on the vehicle, tuning it, testing systems, but need the power disconnected frequently as you adjust/test/remove/install, it becomes a bit ridiculous.

Sure, you could just remove the rear carpeting, remove the spare tire (or sub woofer), open the battery door, and work with the ground strap at the battery end like a normal car. Except the access to that becomes as big of a hassle as messing with the wingnut when you need the car buttoned up between each reconnect.

It's not about battery drain. It's not about being lazy. It's about facilitating work on a car that requires very frequent disconnecting of the battery and not wanting to put additional strain on aging electronic systems.

We're not talking about a shoddy setup with undersized or poorly insulated components, or permanent modifications, or unsightly additions. We're talking about adding a few inches of higher grade ground strap to move the point of disconnect a few inches over.

I'm happy for those that have infrequent need of disconnecting their car's battery. One day, I may remove my disconnect. But while I still tinker with the car, it's been one of the biggest time savers. And, I'm glad to no longer have to stress over all of that intermittent and poor contact parts of the whole operation.
User avatar
By Crumpler
#44134
Got mine today, apparently the package was in USPS geospatial orbit for a week!

Looks awesome, build quality looks industrial performance. Thank you Chris.
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