This info was extracted from the standard 122 Wiring Diagram located in the back of every Service Manual, and even the Owners Manual.
Electrical Troubleshooting Notes 7/07/R. Kwas
As a practical example of some troubleshooting which a vintage Volvo owner might need to do, the Directional Signals and Fuel Gauge are considered...
Use the information I have carefully prepared and presented here in good health and at you own risk!
Troubleshooting Directional Signals A typical problem is: A directional blinker quits working!
Bulb Failures: It's always a good idea to check the simple things first...getting an engine replaced just because you ran out of fuel is equally bad (and expensive!) practice!...and to also take into account other bits of relevant information available at the same time. In the case of the blinker, that means: Even though blinker is non-working, can the tell-tale clicking of the blinker element still be heard from under dashboard?...is the dashboard indicator blinking (possibly at an abnormal rate)?...and the other lamp on that side is blinking as expected. If the answer to all of the above questions is yes, a closer inspection of the suspect lamp is in order. One could start by removing the lens at that corner and just looking at the bulb. Proceed with a visual inspection only.
If one finds a bulb which has soot plated on the inside of the glass envelope, the bulb is due for replacement. The soot is a result of particles of the incandescent filament having burned off, and combined with oxygen which has found its way past the bulb seal, the filament may even still be lighting fine, but the light is not making it through the blackened glass! Finding the glass envelope looking like a mirror is a similar situation where the metal of the filament has plated onto the inner surface of glass. Finally, an open filament will obviously cause a bulb not to light either. In all of these cases, bulb replacement is about the only course of corrective action.
Connection Failures at the Lamp Socket: If however, the bulb doesn't look abnormal, a poor connection may exist. If we remove the lamp, just the action of moving the bulb alone may restore an iffy connection and allow it to work...for a while. That is why I prefer a power-up test here. Turn IGN ON, activate blinker, and wiggle bulb in its holder...sometimes, the bulb will start working for us right there! This suggests a connection failure. Turn IGN OFF, remove bulb and inspect for green or white oxidation dust on bulb base and/or socket...this is often the cause of a poor connection...clean the metal surfaces of bulb base (emery cloth, wire brush) and socket (rolled up emery cloth, mini wire-brush) to shiny fresh metal...especially in the area of the locking pins on the bulb base (because these are typically the actual current path, after they are pressed into a receiving groove in the socket under spring pressure), and when everything is nice and shiny-clean, put a film of ACZP on the bulb base (especially those retaining pins) and reinstall in the socket. Perform another power-up test to confirm your repair and reinstall the lens.
General Blinker Failure: If on the other hand, none of the blinkers are functioning, no clicking of the blinker element can be heard, and the dashboard indicator is showing no signs of life, it might be better to look a bit further up the path...like to Fuse 1 or even the blinker element. In the case of an open Fuse 1, the blinker failure would be associated with non-functioning fuel gauge, wipers, ventilator and a brightly lit AMP Indicator.
Blinker elements used on vintage Volvos were two connection types (this type has no separate output for the indicator), and these must be replaced with two connection types. Be aware that three connection types are apparently not compatible, as this owner found out here...Link to Brickboard Thread (...can't find it at the time of this writing).
As can be seen in a detailed extract of the Wiring Diagram following, power to the Indicator is supplied by the Directional Indicator side circuit, selected with the Directional Lever, and the other side of the Indicator completes the circuit to chassis through the other side’s two bulbs. The technically experienced reader will observe that this puts the dashboard Indicator in series with the two Indicators on the fender which reduces the voltage at the dashboard Indicator (most voltage drops across dashboard indicator, therefore lighting it, only a small amount of voltage drops across the effective resistance of the two bulbs at the fenders, not enough to light them, the effective impedance and Ohms Law is the reason, but a detailed derivation and presentation are not necessary here)...the point is, this is correct, and that also explains why the dashboard Indicator bulb burning out is so rare - the bulb is being operated at an under-voltage and being “soft started” (that is, not being slammed ON with an instantaneous application of the full voltage), and will therefore likely outlast the driver, and maybe the pyramids!
Note: The Blinker element used in the self-contained E-Flasher Switch (where the blinker element is located on switch's back end, and which I prefer for retrofitting on the vintage vehicles LINK) is a three connection type.
This info was extracted from the standard 122
Wiring Diagram located in the back of every Service Manual, and even the Owners
Manual.
A closer look at the detailed circuit diagram shows for instance, that the path of directional signal current is routed by way of the (P) terminal of Wiper Switch and Fuel Gauge. This “daisy-chain” routing explains that if the directional signals don’t work, and we are trying to locate the open circuit which is causing the problem, it may be sometimes become necessary to check places which are not immediately and intuitively involved...here is where some careful and thoughtful interpretation of the wiring diagram is required...and a little logic (or common sense) wouldn't hurt...so if none of the directional signals are working, the supply side, like blinker element and Fuse 1 would be a good place to investigate... If on the other hand, just one corner is not blinking (and the corresponding side on the other end of vehicle is blinking), just that one bulb may be out because of simple bulb failure. Don't forget those six pin connectors...they're highly reliable, but could probably benefit from being pulled apart and pushed back together a few times...and treat with a dab of ACZP.
Happy troubleshooting!
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Background: Fuel gauge itself is a reliable dual coil instrument designed by VDO. It works by electromechanically balancing the magnetic field created by the sensor current against a magnetic field created by an internal reference current. Link to additional info: Drehspulinstrument datasheet. This design is accurate and quite immune to variations in the supply voltage...internal temperature compensation was also built in...quite a good design for automotive application. Inaccuracy stems predominantly from the nature of sensor used and the geometry of its lever arm with respect to the actual fuel level. Often gauges are very non-linear...Full...Full...Full...Full...Half...Empty is the way they like to read. One can try to play with the float lever, but I just try to get accustomed to the way each particular car reads.
Correct operation: The sensor nominal value is from 0-10 Ohms when tank is Empty to 180 ohms. when the tank is full.
Erroneous readings:
Bouncing readings: Sharp, instantaneous bouncing can be a result of an instantaneous resistance change caused by a scratchy contact of the slider arm to the resistance element within the sensor. Surface corrosion can also build on the resistance wire of a stored vehicle, preventing a good contact initially after returning the vehicle to service...this may correct itself as the slider cuts through the corrosion and cleans it away. Erratic readings may also be caused by wiring problems between gauge and sensor, or even a poor negative connection (made through one of the gauge mounting nuts), so both of these should be clean and snug.
Soft bouncing is typically the result of the float bouncing around as the fuel sloshes around the tank during “spirited driving”.
Gauge read Full whenever Ignition is turned ON.
Caused by the highest resistance to chassis/lowest current on the sensor line...this can also be cause by an open connection anywhere along the path...including an open chassis connection to the tank or sender housing.
Gauge read Empty whenever Ignition is turned ON.
Caused by the lowest sensor resistance to chassis/highest current in the sensor line...again, good chassis connections are required.
Fuel Gauge connections showing a bit more detail than usual.
Link to Brickboard thread on fuelgauge: http://www.brickboard.com/RWD/index.htm?id=978149
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Any comments on this information are welcome (and will be given a careful technical consideration, scrutiny and the odd wisea** comment if I can possibly work it in!). R. Kwas
