You can read for 12 volts from each side of the fuse with red meter lead, keeping the black lead on the negative battery terminal or a frame ground.

One problem with checking for voltage across an open fuse is that you need voltage AND load connected, which might not be there depending on position of ignition key. Another way is to (a) - unplug the underhood alarm switch to prevent alarm from waking up; and (b) disconnect positive leg of battery. Then you can read for ohms as usual. In the old days, before digital meters, attaching the ohm meter to a powered circuit might read forward, or backward, or blow the fuse inside the meter.

If using a test light across a fuse it can also glow if power is there.

A fuse can look good, have a crack inside, etc. My pal and I once were sporting about in his brand new 200 series lifted Dodge Power Wagon, and he ran out of fuel in one tank and switched to second tank. Would not run. 2nd tank was full, but the fuse for the solenoid was cracked under the cap, we figured this out and wrapped some tin foil around it and got underway. Not before we looked pretty stupid and blocked a lot of traffic on Ponce De Leon in Atlanta. Lesson learned, carry spares and run first on tank that requires energized solenoid.

 

Sorry, Im confused about what is being tested by your suggestions.

Are these to test to see if current is going to fuses?

Is that also how I would know if power is going to the fuse box?

 

If you have the same voltage reading to negative ground reference (battery terminal or frame ground) on each side of the fuse, then in most cases the fuse is good, and has voltage at the fuse. If you remove the fuse you can check it with the ohms scale.

Now for the question of is there power, most meters are so sensetive that they can read 12 volts even if there is a good bit of corrosion between the battery (source) and your test point. You would want to attach a load and measure the voltage then with load attached. An example would be a tail light bulb. The bulb should glow brightly, and the volts reading on the positive side of the circuit stay almost exactly where it was with no load. If the bulb does not light, or glows dimmly, the circuit has too much resistance somewhere.

Note - I am often referred to as a dim-bulb.

 

Ok, so this one would be continuity test for fuse integrity?


How do I specifically test if power is going to the fuse boxes under the steering wheel?

Check for current across the fuse inputs?

 

Check the voltage on each side of the fuse to a ground point.

 

Ok. And based on this...

Connect the black lead to a ground. Use the red lead to probe the terminals of the fuses. If both sides read about 12 to 13 volts, the fuse is good. If one side reads about 12 to 13 volts, and the other side 0, the fuse is blown. If both sides read 0, that fuse is only fed power with the ignition on, and you need to turn the key to the "run" position and check again. Car engine not running, but key in the position as if it was. If all fuses read 0 on both sides, the black lead is not on a good ground.

...I want to have both fuse points measure ~12 volts with key in pos. 2?

 

yes, in position 2. Some fuses are hot when truck is off, some are switched on at position 2.

 

Thanks again for the tips. Will report back after work.

 

Turn the ignition to position 2 while doing this.

 

Without further ado...

Voltage Rundown

All voltages taken with key in pos. 2

All engine compartment fuses read 12v on both sides.

86v - Sat1-5 (anti-theft alarm), Sat1-3 (engine mgmt), main 13(Ignition feed for Multi-function unit), main 14 (Instruments, reversing lights)

12v - Main 6 (lighter), Sat2-1 & 2 (windows), sat1-1 (anti-theft_alarm), main 12 (MFU)

The headlight fuses (Main 4 & 5) show 0v when off, and .25v when switched on. The headlights work.