automotive wiring diagrams

Discussion in 'General Electronics Chat' started by hafcanadian, Mar 22, 2010.

  1. hafcanadian

    Thread Starter New Member

    Mar 22, 2010
    Every so often I have to read an automotive wiring diagram when trying to diagnose some problem, whether for myself or for friends. I frequently either forget what a DC electrical symbol or identifying letters mean, or run across some I haven't seen before.

    Is there a resource for identifying 12 volt wiring diagram/schematic symbols? I've looked online with limited results, and a lot of the symbols I wonder about are frustratingly not listed in the guides I've seen.

    Two that have me stumped in my current effort are:

    (1) the characters "TB2-11" next to a device on a wire between a relay and a solenoid, and the device is drawn to resemble a single bullseye - it looks like the two bullseyes inside the diagram's rectangular symbol for Circuit Breaker (CB); and

    (2) the letter "S" with various numbers, such as "S1" or "S9", etc., drawn either in a single wire run or at the juncture of two or perhaps many wires - is that a Sensor or just some sort of junction block Stud or something?
    Thanks for any assistance.

  2. Externet

    AAC Fanatic!

    Nov 29, 2005
    Hi Joel
    Every manufacturer will use the notation they want on schematics, and themselves may change it trough the years. Even the same brand and year can have differences if designed in Japan or in Kentucky.

    TB2-11 may mean a connector, a subassemby, a location code, anything. Even thermal breaker two for circuit eleven.

    S can be splice, sensor, switch, or anything not starting with S.

    A decent schematic must have an explanatory chart of meanings somewhere or in nearby pages. Give it a good look.
    Educated guess should give a near truth on its meaning, if you feel it cannot be ignored.

    If you were able to post a page scan, we could find a better answer.
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    TB is a common industrial notation and indicates a Terminal Block.
    TB2-11 would be terminal 11 on block number 2.

    In your case, it could literally be a screw terminal connector, but in a vehicle it's more likely to be a blade/faston connection on a fusebox or other item.
    It's also possible that it indicates a pin in a multi-way connector.

    (As Externet says, terminologies don't always fit the usage - it could be a notation from decades ago when the wiring was done by hand and used screw teminal strips and the form of notation has not been updated to match changes in components).

    The 'S' does not ring any bells without seeing an example schematic, sorry.
  4. hafcanadian

    Thread Starter New Member

    Mar 22, 2010
    Thanks Externet and Robert for the input. Probably I have trouble deciphering diagrams because automotive wiring design outfits can use their own codes - since there is no standardized format beyond the obvious, I can't get them square in my "lay" person's brain. You didn't comment regarding any master code resource, so I reckon I now know why.

    Attached is a section of the diagram I'm working with, trying to trace a faulty motor home entry door seal problem for a buddy in club forum. I think you have helped me eliminate search time by explaining "TB2-11", because we might have physically bumbled through miles of tightly bundled wires looking for a possibly faulty "thermal breaker", even though it didn't make sense for one to be in that circuit. A terminal block we know where it likely is and can check the lockdown screw for tightness. The "bullseye" must be a screw terminal block, and resembles the CB21, for example, because the circuit breakers have in and out screw terminals.

    I assume the icons that resemble bullet connectors in the wires and are marked with text/numbers that start with "C" are just that - Connectors. Some share the same "prefix" though, even though they appear to be on different wire paths, i.e.- wire 232 engine crank has connector C4-26 as well as connector C1-2 and C51-2, but wire 409 has C4-28, C1-21, and C51-21. I realize there are no two connectors with the exact same full ID, but can you illuminate me as to why some share "C1-", for example? Are they together in a single "C1" multi-ported connector?

    Any ideas what the "S1", "S2", "S9", splices mean? Just simply that, a "splice"? If so, what sort of splicing device might we be talking about, so I know what to look for?

  5. Externet

    AAC Fanatic!

    Nov 29, 2005
    With no doubt, S1 is a screw post where the big battery + cable ends with its terminal, and several other smaller cables, each with a terminal that fits such screw post connect to supply different circuits as lights, fan, pump, ...
    Most US GM cars have it under a red plastic cover near the battery to 'spider' +12V towards several circuits, as alternator, lights, keyswitch, trailer connector, ...

    TB2-11 is the same type of bolt post probably much smaller, to accept terminals from cables.

    CB21 is no doubt a circuit breaker. It even looks exactly in the schematic as it would holding it 'belly up' on your hand. A little box with 2 screw posts and nuts on them.

    C4-28 as example, should be a press-in male/female spade or round terminal pair connectors, as many other connectors in the schematic.
  6. Pencil

    Active Member

    Dec 8, 2009
    Just a quick note. Anyplace where a number of wires pass through
    a bulkhead (firewall etc.) this may also be a connector (a "bulkhead" connector).
    See if this may account for many connections with the
    same "C" prefix. One example is: ECM inside cabin, Throttle position
    sensor in engine compartment, C51 is bulkhead connector in firewall,
    pin 7 8VDC, pin8 wiper on pot, pin3 SENSOR COMMON.
    Last edited: Mar 23, 2010