no 12v power to dme relay socket pin 86

[moalaska]

ok i was test driving my car after doing some exhaust work and my car sputtered and died. it restarted and when i pulled into driveway died again. would crank just fine. car starts when dme relay is jumpered. however i don't think its the relay, i tried 2 other spares and neither of them work. when i take cover off relay and close contracts manually it operates fuel pump and i can hear other power turning on with the other contact. i tested switched power at pin 86 on the dme relay socket and i get 0 volts with ignition off or on. from what i read im supposed to get 12 with ignition on. so where to look next?? where does the 12v ignition power come from, i know it comes from the ignition switch, could this be computer related or could i just have a bad wire or switch?? what if i jumpered pin 30 and 86 to simulate the ignition being on? anyone know the wire color under the dash for the 12v ignition switch wire that goes to the dme socket? i thought i just had bad dme relay but this is a little more interesting and i can drive the car around if i jumper the dme relay as if it were bad

[moalaska]

oh and related/ unrelated if i turn ignition to on position after about 30 seconds the tach starts bouncing and then pegs all the way clockwise. maybe something is grounded out in the ignition switch?? all guages recieve power in on position.

[dgcantrell]

Yep sounds like the ignition switch. When the ignition is on, terminal 86 should have power to it. This turns on the DME relay.

[moalaska]

ok does anyone know which color wire off the ignition switch supplies power to pin 86? i read somewhere about two red\black wires supplying switched 12vpower. i would like to eliminate faulty or grounded out wire or connection before i buy something

[Leo944]

I posted a link to the Porsche shop manuals earlier. Download #4 - Electrical.

Porsche Workshop Manuals & Parts Catalogs

[moalaska]

ok from what i can tell the wire comes off the ignition switch a black wire, it splits and one leg goes to pin 86 and the other to the ignition coil its a black wire there. so i would assume that the car wouldn't start at all if there was a break in the wire before the split because the ignition coil wouldn't recieve 12v power. but if there is a break or its grounded out after the wire splits, the coil would recieve power but pin 86 wouldn't? can someone confirm my reasoning?

[moalaska]

i actually get .25 volts to pin 86 so maybe broken wire or grounded out. and the black wire to the coil gets 12 volts.

[moalaska]

does anyone know which connector under the fuse box contains the ignition wires for the dme relay

[moalaska]

ok so i think i figured out wiring. on the electrical diagram it had little letters and numbers next to the wire, for example g23 g25 g14, those correspond to the letters numbers stamped underneath the fuse panek next to each spade connector for the wiring harness. my black wire gets 12 volts where it goes into the fuse box, between there and the relay its. bad. i can disconnect it there and run a jumper wire I guess to the relay, dont know what kind of mess of wires are inside if i split open the fuse box

[bell]

what year car? the factory alarm modules can cause similar issues, if late car is mounted by the dme, you'll need 2 jumpers....

[moalaska]

already disabled the alarm, 87 turbo