Relay pin function
 

The standerd black round relays installed in most porsches is the point of my question. Can anyone tell me what each pin does on those. I am looking on installing one in 1 of my cars as a fuel pump relay. Right now it is wired so that anytime the accessory is on the pump runs. I want to use the relay as a safety thing as I have carbs on this car and if were ever to get in a fender bender this would shut it off. I believe there are 5 pins and I just want to know what each function is. I know 1 is ground, 1 is power, 1 is accs,1 exciter, And 1 more but not sure which wire goe where. I know there are numbers stamped on but don't have one in front of me. Any ideas

Ben
77 911s 3.0
75 914-6 2.7 (for this car)

Pins are numbered; look for numbers molded into bottom of relay.
Pin 86 supplies power to relay coil; pin 85 is ground for relay coil.
Pin 30 is power that is being switched; without any power to the relay coil it is connected to pin 87a. When 12 volts is supplied to pin 86 and the coil is energized, pin 30 will be connected to pin 87. The red fuel pump relays differ in the fact that they have a diode between the coil ground pin 85 and the coil power pin 86; this allows the coil to "free wheel" when shut off, reducing voltage and energy across upstream (up circuit, towards 12v source) switch contacts. Jim

Would the blue wire coming from the alternater be a good switching power sorce? I couldn't think of much else that would work.

Thanks
Ben

Uhh, well, only if you don't want the battery to charge. The blue D+/61 wire runs from the fuse box through the low voltage light on the dash, into the 11 pin connector on the electrical console then out again to the wiring harness. The wire is used to energize the alternator field on initial startup.

You want to shut off your fuel pump so fuel doesn't squirt everywhere if you get in a wreck, right?

Intertia-operated fuel switch, available from Smart Racing Products.

www.smartracingproducts.com

Inertia Activated Fuel Pump Cut-Off Switch
One of man's most simple, yet brilliant designs. In a hard accident, if the driver is unconscious or unaware, ruptured fuel lines can spray pressurized fuel with potentially bleak consequences. Oil pressure activated switches will not shut off the fuel pump if the engine continues to idle. We have tested these switches on a G production SCCA car, PCA GT4 car and a Porsche 962 (at rough Sebring) without a single miss-trip. A smart and wise investment.

Inertia Switch: part #935100 $59.95

Let me ask this question although it may be stupid. Is the volatge regulator hot when engine is running only? I need some place that is powered with the engine running only as a switch.
Ben

I suspect not; otherwise why would Porsche have gone to the trouble of adding the air flow safety switch in later models instead of just adding a simple relay? Jim

Do not go near the voltage regulator, you will open up a world of trouble.

How about an oil pressure safety switch?

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=724&prmenbr=361

You can plumb it in to the oil lines for the tensioners, just make sure it doesn't leak.

I would prefer an electrical switch rather than the oil pressure switch. The relay seams to be the easiest way to go. All I need is something that only works with the engine running. Thats why I was thinking of the blue wire that comes off the alt but I believe that to be an acs wire. I may just have to go with that for now. I have been told to go off the coil connection but don't understand how that works. Any body?

Ben

I stand corrected; for the 73.5 T's Porsche used a connection to the voltage regulater to control the realy that powered the WUR.

See the following diagram.

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_1973_CIS_add.jpg

I wonder if this caused problems as it seems to have changed for later years. Jim

Ok so does that mean that is only live with alternater spinning? or live with ignition switch on?

Ben