Small Motors Bring Big Problems

First, you must remember this... Small electric motors are rated in Watts.

And Watts = Volts x Amps.

But Ogre, my car uses 12 volt system.

So what? Cars get 12.6V on full charge battery, 14.7V on alternator... Voltage varies widely, 12 or less on dead battery to 14-15 to charge the battery. Never assume it is 12v, measure it with a good Volt meter at the circuit you are looking at.

But Ogre, over current will blow the fuse.

False. Fuses and Fuse Link are there to protect the wire and not the motors, light bulbs, etc. (One exception... The Inst Fuse to protect the dimmer transistor.) Some circuits, like radiator fan motor, gets power from a Fuse Link and the Fuse Link likely will not blow from an over current motor. There 3 Fuse Links in headlight system and the motors will tear itself apart and almost never has a Fuse Link is blown.

Low Volt means High Current

High Current (Amp) is bad for:

Fan motor for radiator
Fuel Pump
AC/Heater Blower
Headlight Motors
Starter
And much more...

But how do you get high current? From Low Voltage cause by low battery, bad wires, bad/loose ground, and any number of other items.

Remember... Watts = Volts x Amps.

Watts is a constant so Voltage goes down then Current (Amp) must go up to meet the Wattage uses. Many circuits usually Hate high current and damage, even kill, relays switches and motors.

Example:

Radiator Fan Motor is rated at 150 Watts and uses 10-11 Amps about 14 Volts normally. But have a mess up ground and now get 10 volt, motor uses 15 amp. Really bad ground? Say 7 volts? Motor uses nearly 21.5 amps! That will blow the motor and/or relay to controls the motor.

Fuel pump use 7-8 amps normally... So 8 x 14 = 112 Watts. Plus Fuel Pump is very small motor and even need gas for coolant as well... Any low volt and high amp means a dead fuel pump is easy. Short in oil pressure sender, bad wire harness, and you new fuel pump will die too.

How do I test?

Note: Do not try to test the Starter circuit using this method. Just replace both battery cables when replacing the Starter. The Starter is rated 1.5-1.7 Killo Watts.

By using a volt meter is obvious but "load" the circuit is not obvious to most people. Normal load is the Motor, etc, but you are trying to see if you got a bad motor or bad/loose wires and ground. You need a Test Load and is cheap is a plus.

Make a Test Load by using one or two Headlight bulb.

Plus headlight bulb gives you a quick test... Noticeable Dim bulb mean bad wire/ground but always use a volt meter to.

Use the meter to test without load and with load. Meter should see the same voltage or very close. If you see 12.6V unloaded and 11V loaded then you likely found you're problem.

I need a quick test to make my fuel pump has good wire/ground.

Warning: Check/repair grounds at G201 & G202. (See Wire Service article.) These two grounds are used by most interior items and the Fuel Pump.

Do the same test. Unplug the motor and test voltage. Plug in motor a test again. But note... Fuel Pump Always Need Gas for Coolant! Put two gallons of gas before you test a new pump. (See C502 in Service Manual, etc. C502 is last place you can disconnect the pump with out dropping the tank.)

I want to make a test load like a motor uses.

Headlight bulb is reliable test to. We can tell you how many Amps to see load is equivalent to motor.

Look up the Wattage the bulb uses.
All headlight makers uses 12.8 volt to test. (See FMVSS 571.108)
So 65W/12.8V=5.1A (65w is high beam Halogen)

You can play mix and match to get Test Load to make motor equivalent that way.