Glen Larson wrote to the list:
>> Looking at the wiring diags. Yes, it has come to this.
>> Found the post at  from Dr. Bob and that helps, but still not clear on it. Specifically:
>> What's the line running along the bottom?
>> 12V? Or ground? How do I find where that is coming from?


All the wiring and bus bars connect to something. There are some standard designations that you should be aware of. Also, some diagrams show the bus connections on the bottom and some don't. Different years mean that different techs were drawing the diagrams. In spite of the purity of the
factory engineering, they were drawn to different standards at different times.

Anyway, some standards for the bus connections:

30 is power directly from the battery. No switch, no fuse, connected by big wires that will melt and cause a fire, etc. Disconnect the battery cable at the rear frame (the infamous 'wingnut' connection) before servicing anything that connects to 30. Note that relays have a 30 terminal that is the power
connection for the contacts. On some multi-pole relays they may be subjugated to 30a, 30b. Be aware that the 30 on the relay doesn't correspond to a connection to bus 30, that's all. maybe the 30 means 'connection before it is switched' and then the two mean the same.

31 is ground.

15 is switched with the ignition switch. This bus is usually live with the switch in the 'run' and the 'start' positions IIRC.

There is another switched bus called the X bus. This is a second power bus that also switches with the ignition like the 15, but has the X relay to carry the load instead of the contacts in the ignition switch. Gets confusing again, since there is this X relay, and there is a relay in position X in the main panel. Of course they are not the same relay.

Many/most of the relays draw power directly from one of these buses. Fusing is almost always supplied in the various circuits after the relay or switch contacts. Hmmm. Things like the wiring to the headlight switch and the like are often not fused. Again, disconnect the battery when working on this stuff, since there may not be a fuse to protect the wiring you might accidentally short out. Fuses are normally installed to protect the wiring between the fuse and the load, but do nothing for wiring between the fuse and the power source. Several folks here have reported damage to a lot of harness metal and insulation from accidental shorts. These are frequently the result of poor quality stereo and mobile phone installs. A tech jams a probe into wires until he finds one that's live, and attaches a scotch-lok connector to it to power the new stereo. Wiring grounds out somehow and you find then that he patched in to the cabling to the fuel pump or the EZK relay or some other critical circuit that is now one with all the other wires in the harness.

>> Is there a map for the connector locations?

Yes. I remember seeing one someplace... Don't have the diagrams handy so maybe somebody else will jump in.


One thing I was either unclear or flat wrong about in that post that Greg Nichols archived, and that's the cross-reference system used on many of the
drawings. The drawing legend describes these as "connections with field data". Looking at the drawings for my '89 car, I see that there are letters across the bottom and numbers down the sides of the pages. The letters are always the same, starting with A on the left through P on the right. They skip the letter I because it can be confused with the numeral 1, but leave the letter O since that's so easy to distinguish from the numeral 0. Right!
The numbers down the sides don't repeat however, and instead they progress from sheet to sheet sequentially. In the drawing itself, you'll see that there are wires that connect to things but don't go anywhere but to a little rectangle with a letter and a number in it. That letter and number represent the place on another drawing where the wire continues. If I was tracing a circuit and found a cross-connect designator of "N34", I would page through the drawings until I got to the sheet with row 34 on it, slide my finger over to column "N", and there would be a similar cross-connect designator, but it would have the column/row designation for the place on the sheet that I just came from. Using this system, the factory can segregate wiring on a page by function, and still show where there are connections to other sheets/systems. The draftsmen who did the diagrams were careful to only have one cross-connect designator in each grid section on a drawing, but it's not a bad idea to confirm that it's the same wire by matching up the wire size and color at each end of the connection.
Hope this helps!

dr bob