Delco-Remy Remanufactured
Troubleshooting the Delco-Remy SI Alternator
The following pertains to an internally regulated Delco-Remy Alternator

Troubleshooting the Delco Alternator is really not that big of a deal. There are always goofball electrical demons with the jeep, but I've found these alternators to be fairly reliable. It is important to note that there are two kinds of this type of Delco Alternator, one called the "CS" and one called "SI". SI stands for Systems Integrated, essentially to announce the internal regulator. The CS covers are riveted together and therefore, it is not serviceable and can really only be tested to a certain extent. Thankfully, they are not as common. Though both the SI and the CS are internally regulated, the SI covers are screwed together and it can be manually full-fielded. Further more there was a first generation (Delco-Remy 10SI) and second generation (Delco-Remy 12SI) SI alternator, either available with varied max amperage and assembly clock positions. Visually, the 12SI cooling fan is quite different from the 10SI, but the main benefit of the 12SI is the greater max output without sacrificing size, it has about the same dimensions. For the most part, I believe most CJers have a 10SI, but I posted the 12SI too, just in case. Below I've listed basic wiring, troubleshooting, and miscellaneous links. happy hunting!

Wiring the Alternator
Click Here
Troubleshooting Charging issues
Click Here
What does "Clock Position" mean?
Click Here
How the Delco-Remy SI Alternator Works
Great pics and rebuild tips writeup writeup
Good History and Background on Delco-Remy SI
Converting from Delco 10SI/12SI to 105 amp GM CS130


pirate4x4 thread
Which Delco model on which vehicle
Converting post 1956 CJ5/7 to Delco SI Alternator
Delco Cross-Reference Information

Basic Wiring
Standard SetupBasic wiring for the Delco internally regulated alternator
Comparing the Internal and External Regulator setups internal and external regulator setups for the delco alternator
Wiring Diagram with "idiot light"

Wiring Diagram without "idiot light"
Note, if you choose to re-wire your alternator around the Amp Lamp, it may require a voltage regulator conversion. Read here.

Wiring Diagrams, Assorted diagrams and electrical links.

Testing the Alternator
Testing the Alternator's charging
Alternator doesn't charge at all
Alternator charges too much
Alternator doesn't charge at idle, but does charge at higher RPM
Alternator Full Field test
Testing Specifications

Testing for Charge
The best way to check the charging system requires the use of a multimeter. This is an inexpensive and useful addition to any toolbox, and is available from automotive and tool suppliers such as Canadian Tire or Sears, often for less than $20.

When the engine has not been running for a while, the battery voltage should normally read about 12.5 volts. When the engine is running, this voltage should rise to about 14 volts. If it does not, then the charging system is not working properly.

Alternator doesn't charge at all.
Measure the voltage on the field terminal of the alternator with the engine running. (Be careful of the fan!) If this reads 12 volts and the battery voltage is 12.5 volts or less, the regulator is probably OK and the fault is in the alternator itself. If the field voltage is at or near zero, the regulator is at fault.

The most common defects in alternators are worn brushes and burned out diodes. To check the brushes, shut off the engine, disconnect the field wire from its terminal and measure the resistance from the field terminal to ground on the alternator case with the multimeter. It should be very small; only a few Ohms. If you don't have a meter, connect a piece of wire from the positive post of the battery to one terminal of a small 12 volt lamp. Connect a wire to the other side of the lamp and touch it to the field terminal. The lamp should light. If it does not, or if the resistance reading on your meter is infinite or very high, the brushes are most likely worn out, especially in an older car. Brushes are available from most automotive electrical repair shops, and cost about $5 to $10 a set. If the brushes are OK, then the diodes are likely in need of replacement.
Source Page

How to test an alternator and bypass the regulator

If it is suspected the alternator isn't charging the battery, the best indicator is voltage. When the engine is running, the voltage should be aproximately 14.7 volts DC on a fully charged battery. If the voltage is less than 14.7 VDC and the battery is fully charged, we can diagnose the problem by "full fielding" the alternator.

CAUTION: Full fielding the alternator can result in high voltage. This can result in damage to the vehicle and or personal injury. At higher engine speeds voltage can be LETHAL!

    Pretest checks
  • Battery connections are clean and tight. (both ends of both cables)
  • Battery is fully charged. (if not charge the battery)
  • Alternator wiring and connections are clean and tight. (everything from alternator to battery)
  • Alternator drive belt is tight and in good condition. ( make sure the belt isn't bottoming in the pulleys)
  • Alternator mounting bolts are tight. (These are the ground path for the alternator)
  • Run engine and check for abnormal noises from the alternator.

After the pretest, with the engine off, check the battery voltage. It should be about 12 volts. (if the engine has been recently run it may be higher, maybe 13 volts or so.) Start engine and run at idle. (a one wire alternator may require 3,000 rpm to start charging) Check the battery voltage. It should be about 14-15 volts. Now, locate the test hole as shown below. If there is no test hole you have a CS alternator, (sorry, take it to an alternator shop).

With the engine idling and watching the volt meter, ground the tab located just inside the test hole with a screwdriver to the case. Take reading quickly. With the tab grounded the voltage reading should be 15 volts or higher. The faster the engine speed the higher voltage.

If the voltage is low, the alternator is bad and needs to be replaced If the voltage is 15 or higher, either the regulator or field circuit is the problem. Either replace the regulator or have an alternator shop check/repair it.
Source page for this data

The Alternator Overcharges.
Generally speaking, if at idle, with minimal accessories running, your battery is being charged at a consistent rate of 14.8-15v or greater, your alternator may be overcharging. Typically, this is caused by one or two things:

  • The Regulator is bad and can no longer control output.
  • The Sensing wire has been disconnected or is seeing very high resistance.

Try jumping the sense wire to the battery positive terminal. If the voltage drops to a reasonable output, then the Regulator is good and either the sense wire / terminal needs to be cleaned or replaced. If nothing happens, and voltage still remains abnormally high, then the regulator is probably shot and needs to be replaced.
Source thread for this data

No charge at idle, but charges at high RPM

This could be caused by several things.

First, the pulley ratio may cause the alternator to spin too slow for these driving conditions. Using underdrive or power pulleys on a street application can cause this problem because the pulley ratio becomes less than the typical street ratio of 3:1.

If the pulley ratio IS 3:1, another possibility is that the alternator is too small or not powerful enough at slow speed for the amp load of the vehicle. Also, the charge wire could be too small or the ground path may have high resistance.

The gauge could be out of calibration. Check the voltage directly at the alternator with electrical loads on to determine if the problem is the alternator or the path to the battery.
Source Page for this data

Testing Specifications

Alternator Models and Output Performance at Various RPMs - Top

Alternator Model Availability and Output Performance (1977 Data):

EngineAlternatorDrive RatioDrive Belts
Gasoline - StandardDelco-Remy 10 SI
12V, 37 Amp
2.33 to 1with A/C = dual 3/8"
w/o A/C = Single 3/8"
Gasoline - OptionalDelco-Remy 10 SI
12V, 61 Amp
2.33 to 1with A/C = dual 3/8"
w/o A/C = Single 3/8"
Diesel StandardHitachi Lt-140-6B
12V, 40 Amp
1.95 to 1Single 1/2"

click image for source pdf
Source pdf for this table

Alternator Output (in Amperes)
Delco 10-SI
37 Amp
Delco 10-SI
61 Amp
Hitachi Lt-140-6B
40 Amp

Source page for this table

Assembly CLOCK Position

There are two halves of the alternator case, front half and rear half. The mounting bosses are at the front half of the case. And the electrical connections are at the rear half of the case. Four screws, spaced equally around the case diameter, hold the front and rear halves of the case together.

Conveniently, the rear half can assembled to the front half at any one of four directions. Industry refers to the assembly position as the �clock� position. Clock position of the SI series of alternators is determined by viewing the alternator from the rear, with the threaded mounting hole straight up. With this view, the receptacle for the two wire plug-in connector will point to any one of the four available �CLOCK� positions. Straight up is 12:00, to the right is 3:00, straight down is 6:00, and to the left as shown in the above photo is 9:00.

Having the different available clock assembly positions provides for proper exit of the wiring from the alternator, in any one of four directions, for use with different mounting setups. With the various clock positions available, the alternator could be mounted on the driver�s side, or passenger side of the engine. And the alternator could be mounted upside down, or right side up. By choosing the proper clock position, the same model number of alternator could be used for many applications. (And it was. Buick, Cadillac, Chevy, Oldsmobile, Pontiac, Chevy and GMC trucks, and machinery of all sorts, used the SI series of alternator, with different mounting and clock positions.)
Source Page for this data

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