1979-1993 & 94 Conv [Subscribe to Daily Digest] |
Bill,
I'd say that somehow you get some positive voltage in the +15 line. Then current goes thru 123G wire - 49 instrument cluster thing part #2 - 47M parking brake indicator lamp - 182A wire and diode 84 - 47E alternator indicator lamp - 195 wire - and finally grounds thru alt brushes and rotor. Nevertheless, here's how this issue should be troubleshot:
- you read the combined instruments and the brake lights diagrams in the Bentley or Saab Factory manual;
- you get some voltmeter (it's worth to have several dedicated modes/ranges like 0-20VDC and 0-2VDC);
- having the brake pedal pressed and those lights glowing you measure the potential differences - i.e. voltages - at each thing like indicator light lamp, switch, ground point, voltage source (an ignition switch, a fuse, etc) to get the idea of where the current comes from and where it flows to.
Re grounds: have your voltmeter in the lower range setting (like 0-2V). If you take some ground point and measure the voltage difference between this ground point and some reference ground like the engine or negative battery terminal and you get less then 0,1V, then this ground is a good one (at least under given conditions, i.e. current flowing thru it). If you get 0.1-0.5V then put cleaning this ground (and checking the wiring around for corrosion) onto the todo list. More than 0.5V: bad ground. More than 2V: no ground at all.
Consider yourself checking brake lights in the rear light clusters (remember to have the lights powered, i.e. brake pedal pressed, all fuses in, battery connected and so forth): with the bulb shining around you put one voltmeter probe onto the negative bulb terminal and another voltmeter probe goes to the #9 ground location point which is in the luggage compartment. And you get, say, 0.5V on the voltmeter. Then you have to check that very #9 ground point against a reference ground (engine, negative battery terminal, see above) - you do that and measure 0.1V between #9 ground point in the luggage compartment and engine body (or intake manifold, whatever). Then this means that the wire - and/or connectors - between the negative bulb terminal and #9 ground point is/are corroded or half-broken.
That's how the grounds are checked, not how you're describing it above.
Good luck,
Zig
posted by 5.18.17...
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