I always thought the gen. light bulb was the resistor.

 

I cant find evidence of a seperate "resistor".The brown wire goes from term#1 on the alt. through the bulkhead conn. and up to the Gen. warning light.Sorry

 

Does this help

[IMG][/IMG]

 

Bad scan...lets try this again....

[IMG][/IMG]

 

You did check the bulb? Right?

Jim

 

I finally found our local corvette repair shop. I got a spade for the alternator wire to the fuse box connection. He said the resisitor could possibly be a diode to control the path of the current to protect the ECM. Never thought about that. I can't remember, how does a diode works. Passes current in one direction only?

Thoughts

 

Function
Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow. Diodes are the electrical version of a valve and early diodes were actually called valves.

Forward Voltage Drop
Electricity uses up a little energy pushing its way through the diode, rather like a person pushing through a door with a spring. This means that there is a small voltage across a conducting diode, it is called the forward voltage drop and is about 0.7V for all normal diodes which are made from silicon. The forward voltage drop of a diode is almost constant whatever the current passing through the diode so they have a very steep characteristic (current-voltage graph).

Reverse Voltage
When a reverse voltage is applied a perfect diode does not conduct, but all real diodes leak a very tiny current of a few µA or less. This can be ignored in most circuits because it will be very much smaller than the current flowing in the forward direction. However, all diodes have a maximum reverse voltage (usually 50V or more) and if this is exceeded the diode will fail and pass a large current in the reverse direction, this is called breakdown.
Ordinary diodes can be split into two types: Signal diodes which pass small currents of 100mA or less and Rectifier diodes which can pass large currents. In addition there are LEDs (which have their own page) and Zener diodes (at the bottom of this page).


--------------------------------------------------------------------------------

Connecting and soldering
Diodes must be connected the correct way round, the diagram may be labelled a or + for anode and k or - for cathode (yes, it really is k, not c, for cathode!). The cathode is marked by a line painted on the body. Diodes are labelled with their code in small print, you may need a magnifying glass to read this on small signal diodes!
Small signal diodes can be damaged by heat when soldering, but the risk is small unless you are using a germanium diode (codes beginning OA...) in which case you should use a heat sink clipped to the lead between the joint and the diode body. A standard crocodile clip can be used as a heat sink.

Rectifier diodes are quite robust and no special precautions are needed for soldering them.



--------------------------------------------------------------------------------

Testing diodes
You can use a multimeter or a simple tester (battery, resistor and LED) to check that a diode conducts in one direction but not the other. A lamp may be used to test a rectifier diode, but do NOT use a lamp to test a signal diode because the large current passed by the lamp will destroy the diode!
--------------------------------------------------------------------------------

Signal diodes (small current)
Signal diodes are used to process information (electrical signals) in circuits, so they are only required to pass small currents of up to 100mA.
General purpose signal diodes such as the 1N4148 are made from silicon and have a forward voltage drop of 0.7V.

Germanium diodes such as the OA90 have a lower forward voltage drop of 0.2V and this makes them suitable to use in radio circuits as detectors which extract the audio signal from the weak radio signal.

For general use, where the size of the forward voltage drop is less important, silicon diodes are better because they are less easily damaged by heat when soldering, they have a lower resistance when conducting, and they have very low leakage currents when a reverse voltage is applied.



Protection diodes for relays
Signal diodes are also used with relays to protect transistors and integrated circuits from the brief high voltage produced when the relay coil is switched off. The diagram shows how a protection diode is connected across the relay coil, note that the diode is connected 'backwards' so that it will normally NOT conduct. Conduction only occurs when the relay coil is switched off, at this moment current tries to continue flowing through the coil and it is harmlessly diverted through the diode. Without the diode no current could flow and the coil would produce a damaging high voltage 'spike' in its attempt to keep the current flowing.

--------------------------------------------------------------------------------
Diode Maximum
Current Maximum
Reverse
Voltage
1N4001 1A 50V
1N4002 1A 100V
1N4007 1A 1000V
1N5401 3A 100V
1N5408 3A 1000V
Rectifier diodes (large current)
Rectifier diodes are used in power supplies to convert alternating current (AC) to direct current (DC), a process called rectification. They are also used elsewhere in circuits where a large current must pass through the diode.
All rectifier diodes are made from silicon and therefore have a forward voltage drop of 0.7V. The table shows maximum current and maximum reverse voltage for some popular rectifier diodes. The 1N4001 is suitable for most low voltage circuits with a current of less than 1A.

Also see: Power Supplies



--------------------------------------------------------------------------------

Bridge rectifiers
There are several ways of connecting diodes to make a rectifier to convert AC to DC. The bridge rectifier is one of them and it is available in special packages containing the four diodes required. Bridge rectifiers are rated by their maximum current and maximum reverse voltage. They have four leads or terminals: the two DC outputs are labelled + and -, the two AC inputs are labelled .
The diagram shows the operation of a bridge rectifier as it converts AC to DC. Notice how alternate pairs of diodes conduct.

Also see: Power Supplies

 

Ok

Check the suspected diode with the resistance circuit on the multimeter. Open one way & 1.6meg ohms the other. On the diode tester .5volts one way & 0 volts the other.
Sound good or bad?

 

I don't know. I checked my car I don't have that diode. Where is it? Buried in the harness?

Why don't you take it out of the equation. Bypass it temporarily and see what happens.

Did you try the test in the book? thats out of the service maunal.

Jim

 

Check for yourself but it seems it should be 10 ohm and 10 watt.

http://www.nk.ca/~zcar/pages/article...lternator.html

 

Interesting diode is also the cause of run on???

 

I looked in the book again. The external diode has to be aftermarket. The only reference is to a "diode trio" which is in the alternator and behind the attaching nuts. It can be removed and tested.

Only test stated is connect meter to single connector and to one of the trio (3 connectors) Should read high then reverse leads and it should read low. do this for all three connectors and if the results are not identical replace the diode trio. No values are provided.

Open it up...is the diode trio even there? I cant see where you would get one which may explain the one you have.

Jim

 

I read the Z Car article. It sounds like that is the type of setup that I have. The bar on the diode is pointed towards the alternator side. The bulb on the Alt. light is roughly 5 ohms. It is needed to balance the circuit after the engine is running. I read that somewhere today. Anyway the diode is located about a foot away from the PCB board on the center console. Reading earlier today from Lectric Limited website, it stated that GM did alot of experimentation on the dash harness in 81. They knew of at least 3 versions of that harness. Maybe I got one of the weird ones. Anyway now that I have found a spade to put back in the bulkhead connector, I can hook the brown wire back up to the alternator and see what happens. I guess I can mark this up as a big learning experience & that all things are not shown in the schematics.

Thanks!

Herb

 

Update,

Alt. Light is now working. Repairing the firewall connection was the problem. The diode in the circuit appears to be ok. I think I will leave well enough alone. Now on to the check engine light.

Thanks for the help!

 

Lets get to it!!New thread???




Jim