CONTROL GP-FUEL RATIO 3800818 - Caterpillar

TractorsOn D4H Tractors, and possibly other machines with very low electrical loads and EMS (Electronic Monitoring System), the alternator will have no output for several seconds. The alternator LED (Light Emitting Diode) will come on. This is probably normal operation for the following reason.
On models with no electrical accessories, or if the accessories are all turned off, the electrical load consists only of the back-up alarm, forward horn, hour meter and the EMS. The current drain on the batteries, in forward motion wihtout using the horn, is only 0.20 amp. The batteries are fully charged one to two hours after start-up. After the batteries are fully charged, a load of only 0.20 amp can cause the alternator to "turn off" for several seconds. During this brief interval the alternator LED will come on. When the low electrical load causes the battery voltage to drop, the regulator will "turn on" the alternator, and the alternator LED will go off.
Correct operation is easily confirmed by checking the system voltage with the alternator LED turned ON. Use either the 6V3030, 6V7070, or 6V7800 Multimeter to check the voltage at the batteries. If the voltage is 27.5 1, there is no problem.
To keep the alternator LED from coming on under this condition, install a 25 ohm, 50 watt resistor between the "R" terminal of the 9G7641 Key Start Switch and ground. This resistor puts a one amp load on the batteries any time the key switch is on.