The large MAXI fuses in the engine compartment fuse block are the MAIN fuses. They supply voltage to several other fuses or circuits.MAXI Fuse #13
in your 1996 Ford Ranger is supposed to be a 30 Amp
fuse (not a 50 Amp) according to the power distribution diagrams as well as the fuse block detail diagram. This fuse supplies voltage to the Powertrain Control Module (PCM) power relay and to the oxygen sensor heater circuits.
Please note that it is NORMAL for this fuse to cause a draw on the battery during vehicle operation and also after engine shut down. The OBD-2 oxygen sensor heater circuit monitors run after engine shut down and key off. This can take up to 45 minutes to complete. After the O2 heater monitor has run, the PCM will go into sleep mode.
When the PCM goes into sleep mode, the battery draw from this fuse will be reduced greatly. If you are performing "ignition-off-draw" tests trying to figure out why the battery keeps going dead, it is best to use an ammeter that has a 1 or 2 amp scale. You should set-up for the test using a shunt bar. Wait for 45 minutes to an hour for all of the computer systems in the vehicle to go into sleep mode, then open the shunt. Your computer memory, radio pre-sets, clock, etc. will continue to draw without ever shutting completely off. Any draw under
300 Milliamps is considered "acceptable
". It is my experience that most vehicles have an ignition-off-draw of somewhere near 150 Milliamps.
The underhood fuse box diagram can be found on page 314 in the 1996 Ford Ranger Owner's Manual.
If you do not have an Owner's Manual, you can get a PDF version HERE