in my quest to figure out this gremlin i have, i did find two hot grounds yesterday. when i asked about the D1 pin on the ecm being a ground, trickster verified that for me, so i physically traced all that wire and different connection points. it was originally attached to the rear of the left head with another wire, which when separated, both read hot with the key on. the one that goes to D1 is acually only reading 5.3 volts, the other is reading 9+ volts. that one (9+) goes in to the cabin by the brake master cylinder, but haven't found out where yet, other than it also reads the same at the SIR relay like thing on the left firewall. i know the soucre it's coming from is inside the car, because i've clipped the wire where it was attached to the head. the other one (5.3v) also goes in to the cabin, but i have not isolated it yet to the source coming from inside the car. anyhow, both of these grounds read 0 volts with key OFF, then 9v and 5v with key ON.

KAM

 

Sounds normal to me. With the grounds unhooked you're reading the computer circuit voltage that's supplied to various sensors, usually five volts or so. Computer has an internal voltage regulator, sends five volts to a sensor which has certain resistance depending on conditions and is grounded to the wires you're looking at. As resistance varies the computer reads the voltage change and reacts as needed. Clean up the ground connections real good and reinstall. The 9 volt reading is probably battery voltage through a component of some sort, relay winding maybe.

 

the voltage is "active" with the known components disconnected. i'm trying to pin-point the source by removing all known hot grounds. the one wire that goes to the D1 pin on the ecm is also spliced to the a/c lo press switch and fuel pump relay, if i recall correctly. i can't verify that for certain right now cuz i am out of town, but i think that's how it goes. regardless, with all of those plugs disconnected from their respective components, the voltage is still there. the other wire that has not been isolated yet may be the actual culprit going in to the cabin and affecting the other one coming out, i don't know. this whole thing has something to do with the lights - any lights in the marker/head/fog lites and/or brakes.

here's another scenario: with the key ON, there is a high-pitch hum coming from the alternator (volt reg?). when i pull the light switch to park and/or head, that hum goes away. if i disconnect that connector, that hum is no longer there, but voltage is still present at those grounds.

and yet another scenario: when i reattach the neg cable to battery, key in OFF, the marker lights would come on dimly and i could hear a popping (like a relay click) inside the car. lights would stay on for a couple of seconds and go out. i disconnected what i think is the fog light relay and the popping went away, BUT now the lights will stay on at all times. so, i have to have my batt disconnected right now... i'm not 100% sure it was the fog lite relay i disconnected because of the wiring colors, but that stopped the popping i had. (wires were blue, green, brown, and a tan) and it is mounted behind the turn signal flasher under the column.


btw, i tried to single out the source by pulling fuses one at a time, with no real joy. if i pull the SIR and GAUGES, the voltage will go away, but not completely by one or the other - has to be both.

 

D1 splices with Fan A/C pressure switch, puel pump relay at S143, then there's another wire from that that goes to S217 via C100 (C7). S217 is connected to the instrument cluster, auto trans gear selector, VATS, and ALDL. Also from S143, it goes via another wire to G112, which is connected to ECM E15 (o2 sensor low), ECM D6 and another wire going to C100 (F8) which goes to S246. S246 is the junction for the Diagnostic energy reserve module, passenger compartment discriminating sensor and forward discriminating sensor. These sensors are for the airbag, I believe.

There's a bunch of grounds for the ECM. D1, D6, D7 are connected. D6 and D7 is the ground for the fuel injector control. D7 goes to G118, which ECM A12 also goes to. G118 also goes to the blower motor, blower motor relay, a/c control head a/c compressor clutch, a/c compressor clutch diode.

 

91Z - you got a pm...

and all these systems you mentioned seem to be affected... but finding it will not be fun...

KAM