You don't need to use 'THAT' relay, but I strongly suggest using a relay - blower motors can draw a lot of current, and switching 10amps is something better left to a relay. A normal 20 or 30amp relay should work for this.

Chuck.H
'89 TurboLookTarga, 348k miles

"That" relay contains a bunch of circuitry designed to prove the engine compartment blower is running before switching on the auxiliary blowers in the footwells. You'll find a bunch more info on it if you search for threads on backdating heat in carreras. I think it might also serve some function for the multi-speedness of the blowers too but memory fails. Or not enough coffee yet.

Basically what I am saying is a basic old fashioned relay will work for the purpose. Best recommendation for the most user friendly setup would be to get heat levers with the switch built in that will start the blower when you need it.

Yes, I know there will be a fair amount of current running through it. I thought if I used an appropriate switch and heavy enough wire, it would be OK. But, maybe I should rig a relay into the circuit. The other thought with a separate switch (vs using the Carrera style levers with the switch) is to be able to open the heater control valves without always turning on the blower. I thought some heat would blow through the system without the blower.

Roger

The only existing relay you need is the rear defroster, and one fuse that feeds it. I used SSI's and backdated the heat to simplify and lighten the car. This is the wiring from my 1973.5 CIS, which differs a little from early 1973's and yours also, but much of the changes are the same. I made my own custom panel to eliminate the excess wiring and move the 14 pin connector forward on the panel to better line up with the '86 engine harness. Using the later electric fan should not be too difficult, but I have not looked into it yet.
http://forums.pelicanparts.com/uploa...1363899078.jpg
http://forums.pelicanparts.com/uploa...1363899171.jpg

Ed,

Fantastic! Thank you. I have never had heat in the car since I bought it back in '98 (the flapper boxes were rusted out). The car has been primarily a DE car since I bought it, so I didn't care. One of my reasons for converting to the 3.2 Motronic motor was to make it more drive-able in Chicago traffic. While it won't see snow or rain, it could see those clear cold early spring or late fall days. I think the auxiliary heater fan could be useful when sitting in bumper to bumper traffic.

Of course, this story sounds much better to my wife than, "I need the 3.2 to keep up with newer cars down the straights at Road America" :D

Thanks.
Roger

I'm also using SSI's and backdated the heating system just like E Sully mentioned, and believe me when I tell you that I get more (and instant) heat than I will ever need without having to use the auxiliary fan setup from the 3.2 motors.

And don't forget without a heating system you won't have any way to defrost your windows on those clear cold early spring or late fall days ;)

I hate to break it to you but the 3.2 L still won't keep up with the newer cars at RA - at least on those long straights. :( I have the original 915 with (I guess) stock gearing. Perhaps some top end speed could be gained with modified gearing - are you planning any gear box changes?

Keep in mind, newer for me is the 80s! I'm installing the stock 915 from the '84, which has slightly taller gearing than the '72 915. After running this car for 15 years with the 2.4 (140hp, then modified to about 160hp) and an open diff, 210hp and a LSD should be fun...especially at under 2400 lbs.

Roger

I don't have a 1972 to check for accuracy, but from the diagrams I highlighted in red what should be eliminated from wiring as compared to my 1973 CIS.
I would think that if you intend to keep the electric blower from the 3.2 you could mount a switch of some kind by the flapper box to activate one of the un-needed relays on the console with a feed from the spare fuse to feed it. It might be okay to just have it turn on whenever the engine is running, except for the wear and tear on the blower itself.
From what I read in the manual, the engine blower is activated by a servo controlled by the temperaature knob between the front seats of the Carrera, opening the ducts and activating the blower when heat is called for.
I don't know how it will work on your year, but I was able to hook the Bk/V from the DME directly to my original Tachometer and it worked well, it did not need the later Tachometer. Also the same with the oil pressure. If you decide to use the later instruments, the original Bk/V from the points to the tach could probably be used for the oil pressure light, which was not on the earlier gage.
1973 Porsche 911 - YouTube

http://forums.pelicanparts.com/uploa...1364047111.jpg


http://forums.pelicanparts.com/uploa...1364047215.jpg

my understanding is that the heater blower ALSO helps cool the engine and may be turned on by the DME

(I just finished putting 3.2 into my 914-6 & test drove it yesterday)

similar wiring conundrums as described above - had to test & verify every connection end-to-end - that also meant pulling everything
out of or down from the dash area - - it's a slow process

be aware that all yrs P don't all use the exact-same colors of wires (close, but...)

- and the gauges have different sender requirements so you have to match them - i.e., the 3.2 has 5-bar oil psi - your '72 probably has 10-bar

- I bo't a PMS adapter 3.2 to oem body harness - lots of the pins are not used so don't worry about them

- for DIY you CAN buy new 14-pin connectors - about $50 on eBay as i recall (I bo't an extra I don't need)

(my car is a "real GT" which had at 911R dual ign engine when it left Werks 1, - so it had a separate wiring bundle for the ign which bypassed the oem 914-6 harness - that complicated the conversion a bit)

- I removed that entire heater & blower setup since i have triad headers w/o heat, so it became irrelevant

( I do have the good-used relay, plate & blower setup FS) ;)

hunt around this site and also the 914World site - you will find complete diagrams of DME & wiring & the various connections - lots of us have been down this road already - it just takes a lot of time to wade thru and get it right

,



.

With respect to the fan, I think I will use a relay. I will see if I can rig a switch to activate the fan using the hand throttle lever. If this proves too difficult, I have an amber illuminated toggle that I can mount on the dash next to the hvac controls.

Here is my control panel. I opted to reuse the '72 panel. I cut a hole for the test plug (Note: Use a 1 1/8 drill. I used 1 1/4 and it's a little big.)
http://forums.pelicanparts.com/uploa...1364132502.jpg

My next task is wiring for the fuel pump. I'm using a Carerra pump in back where the MFI pump was located. The Carerra wiring harness has the rd/grn fuel pump wire going up front to the fuse block, then to the pump. I'm thinking I'll run this wire to the back, and possibly use one of the unused fuse positions on the control panel, then down to the pump. There is a grounding post on the bottom of the pump bracket (nut in picture), which I assume I can use.
http://forums.pelicanparts.com/uploa...1364133236.jpg

Does anyone know what the small black wire with the spade connector is? I know red/green is fuel pump and big black is coil, but I can't find a description for this wire. As you can see, it is grouped with the fuel pump and coil wires in the '84 wiring harness.

http://forums.pelicanparts.com/uploa...1364163233.jpg

That's for the factory ant-theft. It needs power in run and start, same as coil feed.

Why I hate electrical work...
 

OK, I installed a switch on the dash to activate a relay which will activate the heater blower. So far so good. Everything worked fine. Then I decide to check power to the three fuses in the engine compartment, since I want to use one of these to power the blower. I didn't seem to show power at the fuse for the rear defrost and rear wiper. So I turned on the rear wiper to check. Well, I forgot that the engine compartment was open. After a quick bit of nasty sounds, I shut off the ignition. The wiper motor was still making a buzzing sound, so I ran up front and disconnected the battery. Dumb.

So, the least of my issues is a slight chip in the paint on the engine lid from the ligature arm popping off the wiper motor and hitting it. The bigger problem is I believe I somehow damaged the turn signal relay, Hella TBB3 96P 2x21W-12V. When I turn on the ignition, this relay now buzzes, or makes a really fast tapping sound, kind of like an electric fuel pump. The rear wiper motor seems to work fine, but the stereo no longer works, which seems to make little sense When I hold my hand on this relay, I can feel it vibrating, so it would appear that it has something to do with the problem. I checked all the fuses, none blown. My heater switch still seems to work fine.

Does this make sense to anyone, that over stressing the rear wiper motor would damage the turn signal relay, which would in turn kill the stereo? Also, does anyone know where you can buy one of these? Our host does not appear to sell them.

Thanks.
Roger

I found the flasher relay
 

For future reference, the flasher relay can be bought at New-Part.com (again, our host does not offer it). I ordered one. We'll see if it solves the problem.

There is not a lot of information on the rear wiper, but I found this. Your wiring may vary and you would have to confirm what is in your car. I don't see how it would affect the flasher relay. It should have it's own fused feed from the front luggage compartment, with another feed fron the rear fuse panel that seems to be for parking the wiper after the dash switch is turned off. The power should be on when the ignition is in run/start position.
The radio is fed directly off terminal 30 on the ignition switch and does not go through the fuse panels, protection would have to be an inline fuse on the radio feed.
http://forums.pelicanparts.com/uploa...1364734119.jpg

Ed,

Thank you. This will be helpful. I suppose it is possible that the wiring has been changed over the years in some ways. There was an aftermarket stereo installed when I got it back in '98. I replaced the stereo last year, and I think I just tapped into what was already there. It's possible that other wiring changes could have occurred elsewhere. I'm going to pray that it is as simple as replacing the flasher relay, however illogical that may be. If that doesn't work, then it probably will involve some tedious tracing work.

Roger

Relay didn't fix it...
 

Unfortunately, the flasher relay didn't fix the problem. The flasher relay only buzzes when you use the flashers, hazzards, or the parking brake (which sort of makes sense). Also, when you turn on the ignition, there is a faint clicking sound from behind the gauges and the tach needle jumps up to around 2K. When I turn on my new heater switch, the needle moves up a little more, 2.2K. I guess I'll have retrace all the wiring under there and see what's happening.

The worst part is that I want to come home tonight and stuff myself with wings and beer. But I can't do that if I have to lay upside down under the dash checking wires!

Damn electrics!

Roger

Solved the flasher issue...
 

When I started looking around under the dash, I noticed the in-line 3A fuse had blown in the stereo power feed. I replaced this and everything works fine. This doesn't feel 100% right, but it works. The car had an aftermarket stereo installed when I got it 15 yrs ago. There may be some unorthodox wiring here, but it worked fine for 15 yrs, so I won't sweat it now.

On different note, is there a consensus as to the best way to connect spliced wires? Are twist caps and tape ok, spade lugs, soldering? I'm going to insert an inline fuse for the fuel pump.

Thanks.
Roger

High quality non insulated butt connectors are generally considered optimal and is what OEMs use.