88 930 What is the best way run a switched 12v lead to the rear torsion bar?
 

OK so this is for my 88 Slant Nose that has the oil cooler in the rear passenger wheel well along with the oil cooler blower fan.

I just had the NLA fan rebuilt and have a post about helping with the wiring here: http://forums.pelicanparts.com/porsche-911-technical-forum/1134637-oil-cooler-fan-non-op-car-but-works-bench.html
where it was determined that the PO bypassed the factory fuse panel and used a higher amp fuse than the factory 16 amp which helped lead to it's failure.

So my plan is to put a manual switch in the cabin but having a problem thinking of the best way to run a wire to it which is right above the torsion bar. I'll keep the ground connected to the harness as that appears to be OK.

It's a cabriolet so no rear defroster nor rear wiper and the bottom of the 3 fuses in the engine bay appears to not be used, but I'll double check.

I was thinking of maybe pulling power from that which would be an easy run to the fan but how do I run a lead to the switch in the cabin?

I hope I am laying this out correctly, if you look at the above previous post that may help as there are a few pics of the fan in the car, I can provide more if that helps..

I am really stuck here and am hoping someone out there can help.

I appreciate any and all help!

can you run off the fog light switch - there may be an empty 12v "tab"
if not - you can purchase the proper style switch - used for the rear fog lights.
me not certain of amperage requirements vs switch feed/switch capabilities.

That's a good idea, the fan is on the same 16amp fuse as central locking and interior lights.

The real issue is how to run a hot lead from that switch to the fan which is right at the passenger torsion bar, not sure how to cleanly route it.

I'm going to keep the fan attached to the harness ground so just need to run one wire from the switch to back there.

Thanks for replying!

You might consider using a relay. Power from the starter (maybe an in-line fuse), ground and coil ground from lots of places back there. Run the coil hot through from the cockpit where the speedometer wire goes through the firewall. Easy to run a wire through the tunnel to that area from your dash switch. Coil wires can be very thin and do the job.

Walt that is a great idea, really appreciate the thought you put into it. You have me re-thinking the solution that I came up with.
I got a little confused with your following statement, I think I understand what you're referring to but can you elaborate a little bit please: "ground and coil ground from lots of places back there. Run the coil hot..."

My plan, which is very fluid, is to use a remote controlled 12V relay switch that is designed to be a12V battery cut off. Essentially you push the button on the remote and it disconnects the ground connection so you no longer need to open the hood to manually operate the battery cut off switch but I'll have the 12V lead running through it

I'll put the Amazon link below for the remote switch, it can be returned for free, but it's listed at 300 amps which they always exaggerate so I chose it over the others which state a 30 amp max just to be safe. If the Pelican forum filters edit the web site with 'X's' either substitute them for Amazon or just Google: KTNNKG 12V DC 300A Current Max Remote Control Car Battery Disconnect Switch .

I'm thinking of mounting the relay somehow behind the engine bay fuse cover and pull 12V from the engine bay 3 fuse panel. Then with an in line fuse I'll run Ancor marine grade 14 2 and route it from the fuse panel behind the shocks and feed it through the rubber grommet for the oil level sending wire, there's plenty of free space where I can cut a little hole for the wire and then feed it along the charcoal canister hose and then down to the fan.

The relay will be here tomorrow and I'll try it on the bench but I do like your idea Walt, I'm going to sleep on it.

Thanks again, much appreciated as this has been a huge issue, I'll definitley update this post with the results of the bench trial and will also be thinking about Walt's plan.


Amazon link: https://www.amazon.com/gp/product/B0B7QK2ZGT/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Seafood
I apologize. I thought you were adding a blower and oil radiator. I have now looked at your other post. I had no idea that your year Flachbau had an oil cooler located in the front of the rear fender well, and that it had a temperature controlled switch to turn it on. I gather that the oil thermostat which other cars is located in that area isn't there. And I now see that the Flachbau wouldn't have room up front for the oil coolers other 3.2s have (though the '89 cooler version looks really good).

This one year deal doesn't show up in the PDF parts catalogs Porsche has available, at least not in what I downloaded.. Only shows the later, better up front cooler, with no electrical temp sensor in it (they's have used the trusty oil thermostat). Bentley for the 3.2s doesn't cover the Turbo, much less the Flachbau that I can see.

So I was just suggesting, as I see others more or less have, a fairly standard wiring practice: Place a relay close to the device and to a source of high current Positive power.. In this case, you can get positive from the big black battery cable where it connects to the starter relay on an 8mm stud. And there are lots of places in the rear to get a good ground somewhat close to that fender well area. For instance, the transmission ground strap. You could put an in-line fuse on either.

From what your electric motor shop says, 25A is all you need. That 300A part you have purchased is massive overkill, isn't it? Any FLAPS 30 or 50A relay should work fine, if what Porsche used somehow won't work.

That way the wires (and fuses) from the temperature switch (or any additional switch you might want so you can turn the fan on manually? Not sure why here) can be of small diameter, can come off of about any 16A front trunk fuse, easy to route, etc.

But you should have a relay and wiring already in place (maybe cut up a bit, but mostly there). Should be no need for adding another relay, running extra wires, etc. Just figure out what someone messed up, or what part (relay or sensor) failed. The fan was running before it physically broke, wasn't it? When fuses blow, moving to a higher amp fuse is not the way to go normally. Fix the cause of the overload (sounds like your fan could easily have done that when damaged). Maybe trying that explains the add on blade fuse? Note what you were advised - match the fuse to the wire gauge/current draw.

If Porsche did things like they did for the regular front oil radiator fans, they ran (if I read Bentley correctly) the positive power from the on/acc positions on the ignition switch to the fan relay coil, and then ran the coil ground to the temperature switch (screwed into the supplemental oil cooler), which closed to ground when the oil got hot. I'd expect they did the same here, except the cooler and sensor and fan (and relay) are in the back.

Is a relay in one of the sockets on the panel back in the engine bay what Porsche used for this oil cooler blower? Or one of the rectangular aluminum boxes on that panel?

That would make sense. It would require a wire from the front fuse panel/ignition switch in the harness or outside it back to the rear panel for relay coil +, and a small wire to the temp sensor in the cooler would provide the coil ground as needed. To run the fan, there are sources of 20A positive back on that panel (looks like Porsche figured16A was enough for the front cooler fan on the regular fendered cars), controlled by a relay, which could also be the high amp in source for a relay.

Why would you want a separate switch you could use to turn this fan on when the oil isn't hot enough to make the sensor contacts close?

As others have suggested, I think your best bet is to use a VOM to trace wires. Follow one of the fan wires to ground to make sure that is working. If I am right that it runs through the temperature sensor, first off jumper the sensor input to ground to see if that grounds the relay coil. Then figure out how to test that the sensor is functioning - if it won't close its contacts inside, the fan won't run. You might have to remove the sensor to test it by hitting it with a flame or putting it in boiling water. Follow the fan motor "hot" wire to a relay. Trace the hot-in pin on the relay to where it gets its current, and make sure it is, indeed, hot. It will probably be hot all the time. Somewhere in this path will be a fuse (20 or 25A). Then see if turning the ignition switch to run makes 12V show up on one of the relay coil terminals.

An easy way to test a round relay is to plug it into the horn relay socket and beep the horn. Or plug the horn relay into the socket in back and see if that makes any difference.

But yes, if you jumper the relay high current in to the relay high current out (doesn't really matter which is which), you should hear the fan motor run.

Do you have the Bentley 3.2 manual? Page 970-31 and 2 show the wiring for the NA engined 3.2's oil cooler fan, with wire colors. A 16A fuse 2 in this circuit. Alas, they don't show relay pin #s or wire diameters. I'd scan and post a copy, but my scanner is down. Just a guess that Porsche followed their usual wiring and looms for these special order cars as much as they could, including wiring conventions.

Hi Walt, I quickly skimmed through and CANNOT thank you enough.
I wanted to point a few things out, I will post the link to a post I made a few days ago, when I got the fan back from being rebuilt I connected it to the factory harness and I grounded pin 85 of the relay, just what the thermostat does when it gets hot, it grounds that pin.
When I grounded pin 85 the fan turned on, all is great I thought!
I went for a test drive and the fan worked for a few seconds and then died and I could not figure out why, I spent all last weekend trying to figure out why I could not get the fan to work like it did by grounding pin 85 of it's relay.
Walt it was driving me crazy, I skipped going to a couple of different Super Bowl parties as this was more important.

Herre is the post: http://forums.pelicanparts.com/porsche-911-technical-forum/1134637-oil-cooler-fan-non-op-car-but-works-bench.html#post11920672

I discovered that the PO bypassed the factory 16 amp fuse and installed an inline 25 amp blade fuse hidden behind the panel. I spent days tracing everything as you'll see in that post only to discover non factory wiring. I am guessing that the fan was getting full of dirt and kept blowing the fuse so tjey kept sticking larger and larger fuses in there.
When I ran the fan with that 25 amp fuse, remember, I did not know it was there and thought it was using the factory rated 16 amp, it blew the 25 amp and I can only assume it blew it because the PO must have fried the factory wiring harness by increasing the fuse amps.

When I got the car the fan the blades were stuck in place, road gravel was wedged between the blades and the housing and the windings were fried. I can only assume they messed up the factory harness by increasing the fuse and the fan finally cooking itself to death, literately.

I only ordered the 300 amp switch as it seemed more rugged than the 30 amp switches that were the next step down, it will be heavily fused connection so no worry there.

I just wanted to quickly reply to you and show you my post to help explain how I got here.
I am totally open to options and you have given me some great ones and for that I really appreciate it!!! I cannot thank you enough for taking time from your life to help a stranger.

I will update with any results I get from bench testing.

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I just wanted to ensure this point gets the attention it deserves, It appears that I am unable to use the factory harness to properly [power this fan.
The factory had in place a 16 amp fuse that was shared among this fan, central locking and interior lighting.
Given that the PO bypassed the factory fuse and put in place a blade fuse holder with a 25 amp fuse shows that the fan was dying and they kept increasing the fuse to keep it running until it finally died, thereby also damaging the factory harness in one way or another.

I connected the fan to the harness with a 20 amp fuse and it ran for 3 minutes before blowing the fuse, somewhere there is resistance in the wiring blowing the fuses.

Tomorrow (Wednesday) I am going to bench test the fan with a 15 amp blade fuse and see what happens, I'll attempt to run it for no less than 20 mins. and will report the results.

The alleged weakness in the harness is why I am looking to run a new circuit like the post states but let's see if the rebuilt fan can run on the bench for a while, if it does then it is the harness and if not it's the fan.

The picture of your new fan motor shows it is 50 Watts at 12VDC. You should be looking at about 4 amps (maybe starting up adds a few more). On the test bench, use your VOM to measure the amp draw.

You should be able, with some cleverness, to measure the resistance of the wires involved in the power part of the relay. You should be able to discount the control wires which give power and ground to the relay coil, as they aren't likely to blow a 20 or 15A fuse - the relay coil wires are very thin and would melt, or their solder joint would, before the fuse would blow or the external wires would melt.

If the relay connects the motor to ground, a ground wire short ought to mean the motor would run all the time, so to speak. So it is the path of 12 volts to the relay and then to the motor which could have melted and basically shorted to ground.

You are looking at the wires which provide the 12VDC to the motor. With a wire not connected at either end, when you check its resistance to ground you should have almost infinite resistance. If it is a wire connected to the ignition switch (thus not easily disconnected), just make sure the ignition is off. If not infinite or close to it, that is probably your culprit, with the insulation melted off in such a way that the wire connects to ground somehow.

I'd think that if you find that wire and the short, you can replace that wire by running a new wire along its path, using the same holes in bulkheads. The original culprit seems to be the excess current draw (causing a lot of heat) of a physically damaged motor which melted insulation and caused a short after the owner kept trying bigger and bigger fuses.

Simpler than building a whole new system.

I have a rear mounted oil cooler with fan in my SC. I have also deleted the rear wiper.

I just use the original rear wiper wiring and of course the switch is already on the dash. My oil cooler has a thermostatic switch but I use the dash switch as an override.

My '85 slant had this rear fender cooler/fan setup. The PO had it replaced with a front mount cooler, all the old parts came in a box with the car. He may have had similar wiring issues, don't know.
I agree that the most elegant solution would be to repair the current wiring. If that is not feasible I would pull power from the rear fuse panel or use the rear wiper circuit as suggested. I've used the rear fuse panel before to run rear fuel pumps on 911's with 930 engine transplants; very simple and effective.