Where can I safely tap 12v power to add another circuit?

You have a draw on the battery somewhere. The easiest way I have found to locate a draw is to remove the negative battery cable and put a 12v test light in between the cable end and the battery post. If you have a draw the light should light bright. A dim light is normal due to parasitic draw. You can now remove circuit breakers and fuses until the light goes dim. This will give you a starting point as to what circuit needs looked at. I always start with removing the main wire going to the alternator. The alternator can still charge while it is pulling all of the power when the engine is not running if the right diode goes out.

Hi Ron
Thats a tough one.... Starting behind the fuse box....

Start from the other end. All Power has to come from the Battery.
So... a main feed wire (thicker) might be open.

There is another type of fuse used on cars. They are called fusible links. Check the wires leaving the Battery Positive terminal with a MultiMeter. Or use a 12v Test Light or make one up.
There is probably an open circuit in a link cable or Circuit Breaker.

Perhaps a Relay turned on by the Ignition Key is not making contact.
Tap the relay to get the internal contacts better connected. Or remove a suspect & test with 12v to the relay coil & monitor contacts with multimeter.
Sure is easier than pulling the fuse box out
Good Luck

Relay Wikipedia the free encyclopedia https://duckduckgo.com/?q=the+hook+automotive+tester&ia=products

Hi Bobbi
A 50w Headlamp will draw 4 Amps (Ohms Law 50/12=4.1)
So... 2 Low beams will draw 8 Amps.
Obviously more for high beam and high wattage Quartz Bulbs.
That is a lot for a small switch (contacts) to handle.
This is why a lot of vehicles use a Relay to power the Headlamps.
The relay is connected directly from the Battery to the Headlamps.
The large internal contacts can handle the higher current (30A) and the dash headlight switch connects to the magnetic coil inside the relay and is only used to pull the contacts closed.
Does your circuit include a relay.? Do you hear a relay click?
simple headlight relay wiring

To assist with your troubleshooting, try disconnecting one head lamp bulb to reduce current load. Does the fuse blow?
A temporary12v circuit breaker could be substituted for the fuse until you determine the problem.


If the circuit is using a relay then there will be a fat wire going from the battery to the Relay. The fine wire on the relay input is the trigger. A 12v test lamp is really useful for troubleshooting around the car. Also a cheap multimeter. Clamp style current meter is also handy to see exactly what current is blowing the fuse

Relays

http://www.ebay.com.au/itm/NARVA-CIRCUIT-BREAKER-REPLACES-STANDARD-BLADE-FUSE-BATTERY-15A-AMP-12V-55715-/321234642731?hash=item4acb13a72b
There is a 10A circuit breaker also like above

Automotive Circuit Breakers Wiring Products

You have a parasitic draw. Something is drawing power while the truck is sitting. Do you have any aftermarket items hooked to direct power? Something you leave plugged in to the 12V plug (cig lighter) Some 12v plugs are full time power and some are only powered with ignition on. Any amps wired direct power? If you have no aftermarket accessories drawing constant power you then need to determine what circuit has the draw. An amp clamp on the battery cable will show draw, then re & re 1 fuse at a time until you find the one that eliminates the draw. Once you've done that you need to find the problem on that circuit. All this is assuming your charging system is working and the battery is being properly charged while you're driving the truck.

Find the fuse box behind the glove compartment door. See this video.

Most phone charger require less than an amp or two at 12 VDC so you could probably "sneak" the piggyback device in your link above on anything existing - but I'd recommend a higher value fused circuit like a 20 ~ 30 amp types. Stay away from those used for headlights, wipers, etc. Connecting to radio, A/C, Heater, etc may be a better choice. Check your manual to see if there is an accessory fuse slot designed for this purpose.

maybe try getting your 12v feed from the radio power, this should be connected to the ignition switch and will run when the key is turned to accessory or the ignition is turned on

use a 12v car battery and a small battery charger... a winch draws alot of amps when in use... so you need the battery to supply the amperage ... 12v power supplies are low amperage output supplies... so will not work (inexpensively).

Tire compressor probably draws too much current for the socket. Are you sure it is a cigarette lighter socket? Some sockets are just to provide accessories 12v. Did a cigarette lighter come with this socket? True cigarette lighter sockets are generally fused at 25 or 30 Amps

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 (direct link)

all on the same circuit. radio has two power supplys, one when the key on, and one all the time. aftermarket decks draw alot more than factory and this circuit may not be able to handle the extra load. look in owners manual and look in engine and interior fuse panels. it may say memory,clock,ecm keep alive etc. if need be check them all one is failed. now as for the engine light, most obdII vehicles use this circuit to keep computer memory alive... it will set a code for voltage lost. if you know your not overloaded or have a short, then its safe to go up to next size fuse,2.5 or 5 amp heavier. but thats it. if keeps happening you have a short or you may have to run a dedicated feed circuit for the deck. good luck youll find it