A few variables are involved with jump-starting a dual battery-equipped diesel truck, and if you're trying to jump-start a diesel with a single-battery vehicle, there is no guarantee of the results. Some diesel engines have an isolator switch to protect the second battery. It's best to jump-start a diesel truck with an equivalently powered truck. It takes more cold cranking amps to turn a diesel truck over, and trying to jump-start one off a four-cylinder import is like bringing a knife to a gunfight.
Make sure all the power sources are off in the dead vehicle.
Attach the positive clamp of the jump lead to the positive terminal on the battery of the running vehicle, then the negative clamp to the negative terminal on the battery of the running vehicle. Do the same for the second set of jump leads on the opposite battery. If using a jump pack or battery charger, skip this step.
Place the positive clamp onto the positive battery terminal of one dead battery (there may be a red box or jump-start post behind the driver's-side battery on some diesel trucks you can clamp to) and the negative clamp to a non-moving ground connection, such as a frame rail or metal bolt head. Repeat this step for the second set of cables. If using a jump pack or battery charger, make sure both are in the "Off" position and attach the clamps in the same way to the battery on the driver's side, then switch the power to the "On" position.
Try to start the diesel truck. The results can mean different things. If the batteries are completely drained, you may have to allow them to charge up from the charging source--other truck, jump pack or battery charger. If the truck does not start with the jump pack, this option can be eliminated.
Rev the engine of the truck to 1,500 RPMs for a period of time or set the charger to 200 amps (or "start") and try to start the truck every 10 minutes or so. The time needed will depend on how dead the batteries are, how cold it is and the type of equipment you're using.
Unplug the negative clamp from the jump-started truck first, then unplug the positive cable. Unplug the clamps from the other vehicle in the same manner. Unplug one set of cables at a time and be sure to not allow the clamps to come into contact with one another. If using a jump pack or charger, turn the units to the "Off: position first and then unplug the clamps from the truck in the same manner.
The jump leads, battery charger or jump pack must be heavy duty with a gauge wire that&#039;s high enough to accommodate jump-starting dual-battery diesel engines. If you can jump-start your diesel truck off a regular pair of jump leads using a VW Beetle, the cold cranking amps were simply low in the truck and didn&#039;t have enough juice to kick it over. Keeping the batteries in good shape, cleaning the terminals and knowing the age of the batteries are helpful. Keeping the block heater (if equipped) plugged in on cold nights also helps.