AMP Indicator under normal conditions, (Unlit!), …no magic here!
Source: My fertile little mind, info from the wiring diagram, plus MS Paint!
Understanding the function of the
AMP indicator in your vintage Volvo, and how to proceed when it comes ON.
Copyright © 2005
*
Aug 2005 R. Kwas
The info presented here applies to unmodified Volvo (*) 544, 122 and 1800 (Bosch generator) 12V electrical systems, and is intended to help in the understanding of these systems for the purpose of trouble locating and repair after the AMP indicator comes ON. I have long ago upgraded just about all of my vintage vehicles to modern, high output alternators with fully electronic internal regulators, and I’m a big advocate of this, but I thought I would compile this article for those who prefer to remain original, as locating the troubles once the AMP indicator comes ON can be tricky for qualified individuals and totally baffling for the inexperienced. The article is not yet complete and neat, but there is enough info here to get one well started.
Notice: I stand behind all the information presented here, having put it together with the utmost care, but in the end, the reader is responsible for its use and the consequences of their own actions. The information presented should be used in conjunction with normal, cautious shop practice. I will not be responsible for your actions. Work safely!
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Since the deceivingly simple AMP indicator is actually employed in a slightly complicated manner (not to mention that is not even indicating AMPs - that was just a handy - and short, electrical sounding word that would fit on the tiny indicator), a complete understanding of this indicator’s function is necessary. It may, in some circles, be called an “Idiot Light”, but the manner in which it was designed into the electrical system is anything but idiotic…its actually rather ingenious…in a do-the-maximum-with-a-minimum kind-of way!
The AMP light itself is a dirt-simple (2 Watt) incandescent lamp, but the manner in which is cleverly worked into the electrical system allows it to light up and indicate two very different failure conditions. Herein lies the complication. In the first place, in the normal condition (IGNition ON, engine running / all-things-fine), the lamp actually has voltage applied to both sides, and so does not light! Understanding this simple fact is essential to appreciating what is happening here, and unraveling the complication. Reminder: For any electrical device to function it requires voltage across its terminals. This voltage serves to encourage the flow of electrical current through the load, powering it up…and indeed, the AMP indicator as well, must have voltage across it to light!
Reviewing, a complete 122S wiring diagram, it can be seen that, one side of the AMP indicator is connected to Fuse 1 (IGNition power). The other side is connected to, and monitors the charging system output at, the Voltage Regulator (VR) D+ terminal. The reader will note and should understand, that in this situation, with voltage on both sides of the lamp, no current flows, and the indicator remains unlit!
AMP Indicator under normal conditions, (Unlit!), …no magic here!
Source: My fertile little mind, info from the wiring diagram, plus MS Paint!
Again, in order to light the lamp, the voltage-across condition must be satisfied. Only this will allow current to flow. The really observant or electrically enlightened reader will also notice, that this condition may be met by tying either side to ground. [See: Idea 1 below]
The two conditions, which will cause the AMP indicator to light while the engine is running, are therefore:
Condition 1: Fuse 1 open (…at which time, the other Fuse 1 loads complete the circuit to chassis allowing lamp current to flow).
Condition 2: Failure of charging system (…the armature of generator does not produce voltage, but instead, completes circuit to chassis allowing lamp current to flow…for example…when IGN key is turned ON, but before starting the engine).
The “Other” Condition: AMP indicator glows slightly while engine is running. This is a frequently occurring condition known to just about all owners of these vehicles, discussed separately below.
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Condition 1 Checkout of open Fuse 1 causing AMP indicator to be ON.
An open Fuse 1 is quickly verified, as it is accompanied by the loss of function of other Fuse 1 loads…specifically, these are: Directional indicators, Fuel gauge, Blower, and Wipers. If the AMP light ever comes on full, while the engine is running, or does not extinguish shortly after starting, this is the first thing, which should be checked for, as it is the simplest. The driver, even a technical layman can, and should do this…as soon as practical.
Functional test when AMP indicator comes ON with engine running: Turn any of the other Fuse 1 loads ON. If loads do not function, Fuse 1 should be suspect. Open hood at the next opportunity, and with IGN ON and engine running, activate left directional indicators (these are easily seen while standing next to the vehicle on the drivers side). Remove the fuseblock cover (you should know where it is!), and visually check the state of Fuse 1. If the fuse is visually OK (Suggestion: Always install Euro-fuses with element visible to allow for an easy inspection!), spin it in its holder…if this restores the connections so that the directional indicators start blinking (and causes the AMP light to extinguish), corrosion may have been present and breaking the connection. Spinning the fuse has cut through this corrosion at the conical fuse ends, and reestablished a connection… This is actually a rather common failure…on the injected 140s and 1800s, this failure occurring on the fuel-pump relay fuse is also well-known…
…if, on the other hand, the wiper worked when the switch was tried, Condition 2 may exist, or the classic “Other” Condition caused by long-term corrosion. Checkout and correction of Condition 2 will require a more careful investigation of voltages under the hood using a multimeter. This is down-and-dirty technical stuff, and should be performed by someone who is at least familiar with the operation of a multimeter.
Verification of open Fuse 1 (or associated connections) condition: Shut IGNition OFF, allowing motor to come to a stop. Turn IGN to the ON position, but do not START. If AMP indicator does not light, Fuse 1 should be suspect. Explanation: When IGN power is applied, but before starting, the AMP indicator is supplied on one side with IGN power and on the other with a connection to chassis through the non-electric producing armature of the generator. The AMP indicator should light…if it does not, it must be assumed that it is not being supplied with power, and therefore Fuse 1, or associated connections are suspect.
If replacing a (blown) Fuse 1 remedies the condition …it’s a mixed blessing. This is the simplest failure to fix, but one has to wonder why the fuse actually blew in the first place…because actually blowing the 25A rated Fuse 1 is fairly unusual.
If on the other hand, just the action of moving the fuse in its holder (or spinning it) is enough to restore function, that suggests the more common poor connection due to corrosion condition.
Consider yourself lucky for not having a dreaded charging system , but deduct two points for neglect, and, at earliest possible opportunity, clean fuse-ends and the circular connection holes in the clips properly with abrasive, apply Zinc Anti-Corrosive Electrical Paste, and reinstall fuse. Suggested reading: Gas-Tight-Joint Tech article.
Having checked Fuse 1 and found it to be intact, and spinning it to try to cut through any corrosion did not fix the symptoms, another check, requiring a multimeter should be performed before moving on to checks of the charging system. With the IGN ON and engine running, the IGN power should be measured at the Fuse 1 and Fuse 2 (input) terminals on left (Black wires), as well as (output) terminals (Red wires), on right side. If voltage is measured at the input but not the output, an open connection at the fuseblock exists…this may be caused by a poor connection due to corrosion at the push-on terminals, corrosion between the riveted contact plates or conical fuse-ends (as both discussed in the Gas-Tight-Joint Tech article), or a blown or fatigued fuse which was previously missed.
If checks around the fuseblock reveal no problems areas, a failed charging system must be considered to be causing the AMP light to be ON..
Condition 2 Checkout of Charging System causing AMP light to be ON. This is the next thing, which should be checked. It is down and dirty technical stuff, requiring tools, a multimeter and at least a basic understanding of how to correctly put these to use without hurting oneself (knuckles not withstanding).
With engine running, measure voltage from D+ terminal (Generator output) of VR to chassis. If this voltage is less than 2 Volts, charging system (combo of the generator and regulator) has no output.
Regulator Bypass Test: [As the generator is not regulated during this test it should only be performed momentarily...that is, just long enough to perform the test]. While continuing to measure the output voltage at D+, short the DF terminal of the VR to chassis (all wiring normally in place), using a screwdriver or similar at the regulator DF terminal. This takes the place of the VR and completes the path to ground, allowing field current to flow (see: Simplified Charging System Wiring below). An output in excess of 12V should now be read on the D+ terminal, and this voltage should also be measured, without a drop, on the battery plus terminal. Raising the RPMs should raise this voltage, as the generator output comes up. This suggests a voltage regulator problem. Replace VR. Note: Successful repair of the VR is beyond the scope of this article and without calibrated test equipment and setup, likely beyond the abilities of even the most experienced backyard wrencher!
If bypassing the VR does not result in an output, the generator itself must be suspect.
Generator checks.
In-Situ Reciprocity Test. This is a test, helpful for determining the state of health of the generator. It is performed which the generator installed and wired normally, but with the fanbelt removed. A side-effect here is that the wiring from the VR is checked at the same time. A successful test, gives a certain level of confidence in the generator, harness and connections. Performing the Reciprocity Test is simple…after loosening and removing the fanbelt, use two temporary test jumper wires to 1. Connect the DF terminal to chassis, and 2. Connect the B+ to the D+ terminals at the VR. This applies battery power and field current to the generator, and by applying a marvelous principle of science, which states that many processes run backwards as well as forwards, the generator should spin as a motor. If it does not, Generator is suspect. Remove test wires and proceed to…
Passive Resistance Tests. With IGNition OFF, battery plus disconnected, and loose fanbelt, disconnect the D+ and DF wires from the generator. With the multimeter in the Ohms function, verify the internal connections as shown in the graphic following. The D+ terminal (Armature output, which runs through the brushes) to chassis reading should read about:: 50 Ohms, remaining fairly steady and without a lot of fluctuation when spinning the generator pulley in the normal running direction. The DF to D+ terminal should read about 4.8Ohms, unaffected by a spinning armature. This is a basic check on internals of the generator as shown below. Note that the power connection for the field is permanently made, within to the generator, but requires an external connection to chassis in order to allow field current to flow. This in fact is, what the VR does as it monitors the system voltage against an internal reference, and what the troubleshooter has done, manually, when performing the previous Regulator Bypass Test.
D+ DF
Source: Volvo Factory Service Manual
Poor Connections! Don’t discount these, since poor connections are a definite possible cause of electrical problems, especially on a 40 year old vehicle, it wouldn’t be such a bad idea to assure all connections are clean and tight before starting to replace expensive electrical components. One would feel pretty silly if hours of troubleshooting and expensive replacement work were all for naught, if a problem turns out to really have been caused by a corroded or loose connection!
Zinc anti-corrosive electrical paste is the Anti-Seize of the electrical world! Use this paste after disconnecting and cleaning electrical connections of the vehicle. The connections critical to the charging system are, voltage regulator (including its mounting bolts which make the connection to the vehicle chassis!), generator, battery, starter, IGN switch, fuseblock, groundstrap (connecting chassis and engine).
The “Other” Condition: AMP indicator glows slightly. The well-known condition of a dimly lit AMP light is not a separate condition, but a variation of Condition 1. It is caused by the slight voltage drop, which occurs, by design, across the Fuse 1**, as the indicator lamp is a small, sensitive lamp, even a slight voltage across it will satisfy the voltage across rule, and cause a slight glow of the lamp. This is absolutely normal, and even occurred when the car was new! If however, additional voltage drop occurs due to poor connections, the voltage across the lamp increases, and the lamp glows more brightly.
This condition is particularly evident when turning ON the blower motor, as this load draws the most current through the circuit. This in turn, causes the most voltage drop across the intentional resistance of the fuse, and added to that the voltage occurring across any unwanted poor connections, which puts even more voltage across the lamp.
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Summary
In order to light the AMP indicator, the voltage-across-condition must be satisfied. The two conditions are:
1. Fuse 1 open
2. Failure of charging system.
Given good connections, there are two conditions under which the AMP indicator may light, but add to that, frequently occurring faults due to subtle corrosion and/or poor connections, locating and remedying the trouble can get complicated…fast!
Following an order of Simplest-to-Complicated fault isolation, check Fuse 1 and associated connections first, then Charging system, breaking this into Generator, then Voltage Regulator, components.
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Voltage Regulator (VR) function for a generator electrical system explained:
1. The VR’s main function is to control the electrical system by monitoring system voltage and activate the generator to contribute electrical power when system voltage (and therefore battery charge) is low.
3.
A second function is required in generator systems. That is, to
disconnect the generator from the battery when the IGN is OFF and generator is
not contributing (in fact, the generator would take (and waste) battery power if
left connected under this condition).
Simplified Charging System Wiring Diagram
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** Review: How a fuse works:
A fuse is an intentional weak electrical link, which has a small but important resistance (R - Ohms) to the flow of electrical current (I - Amps). As current flows to the downstream load, this resistance causes a small voltage drop, which in turn causes power dissipation (P - Watts) to occur (also known as I2R heating). As the current increases, so does this heating (exponentially in fact). By designing and constructing fuses carefully, these can be used as simple, effective, circuit protective devices, with a predictable (normal and expected) level of current which will be allowed to pass, and a predictable amount of (fault) current which will not be allowed to pass. The fuse “blows” (melts, breaking the connection and thereby power delivery to the load), when excessive current is drawn by the circuit it is in series with.
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Idea 1. It is easy to see that depending on which side is supplying the power and which side is supplying the ground (return current path to battery negative), determines the direction of current flow through the indicator. This immediately brings to mind those cute little bi-color LEDs, which have two different color LEDs in one package, back to back, and so light up differently depending on current direction. These might be nice to use here…Green for Fuse 1 blown, Red for Charging system failure.
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Legal Notices: The terms Volvo and Bosch are used here for reference only. I am not affiliated with Volvo…although I do also Roll…or Robert Bosch. Close cover before striking. Use your directional indicators…. It’s a car, not a phonebooth! Your mother wears army boots, blah, blah, blah…
The contents of this article are Copyright © 2005 by Ronald Kwas. You are welcome to use this article and its contents for non-commercial purposes. But if you copy and republish it, whole or in part, without giving credit to the author, or linking back to the Sw-Em site as the source, you’re just a lazy, scum sucking plagiarist! Go work for the Boston Globe or something!
Comments on this article are welcome.
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Notes / References / Additional:
Link to Zinc anti-corrosive electrical paste.
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Additional: The official green Volvo Service manual calls for a nominal field coil resistance of 4.8 Ohms. No armature readings are given. After a call on the Brickboard and Volvoniacs fora, for actual resistance readings on generators made, some helpful owners (Thanks Phil, Joe, McMike ) provided readings on known good units, and also suspected bad units. The typical good readings are included in the previous text for reference. The readings from suspected bad units are included below along with comments to help owners troubleshoot these generators. Finally, service recommendations are made for repairing the non-working units.
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D+ to D- (Armature, static): Open (infinite Ohms)
D+ to D- (Armature, while turning): Open
DF to D+ (Field only): Open
Comments: When making resistance measurements on old, possibly less than clean automotive components, its obvious to assure good connections are made…so the first thing I would ask in response to these readings is: Are your sure you were making a good connection with the meter probes? If the answer is: “Yes”, the second thing I’d ask is: Are there any guts in the thing or is it perhaps just an empty shell?
Service Recommendation: Open inspection band, retake readings on wires or connections inside to verify, if no change, disassemble totally, and recheck Armature and Field resistances while apart.
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D+ to D- (Armature, static): 48Ohms
D+ to D- (Armature, while turning): Bouncing from 20 to 200 Ohms
DF to D+ (Field only): 4.8 Ohms
Comments: Possibly worn brushes, possibly a contaminated commutator, or both. Field resistance is nominal, so this generator has possibilities!
Service Recommendation: Open inspection band, check height of brushes and color of commutator, using emery board clean commutator to a shiny copper, clean using carb cleaner or brake cleaner solvent to flush (conductive) dust from brushes, and copper particles from commutator clean-up, then compressed air to dry.
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D+ to D- (Armature, static):
D+ to D- (Armature, while turning):
DF to D+ (Field only):
Comments:
Service Recommendation:
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D+ to D- (Armature, static):
D+ to D- (Armature, while turning):
DF to D+ (Field only):
Comments:
Service Recommendation:
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D+ to D- (Armature, static):
D+ to D- (Armature, while turning):
DF to D+ (Field only):
Comments:
Service Recommendation:
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D+ to D- (Armature, static):
D+ to D- (Armature, while turning):
DF to D+ (Field only):
Comments:
Service Recommendation: