Vehicle: 1996 Ford Ranger
Trim: XLT
Drivetrain: 4x4 with Electronic Lock System
Cab: Extended w/ Jump Seats
Engine: 3L V6
Transmission: Mazda R1 5SPOD
Modifications: Aftermarket Stereo (Self Installed); Dec 2019 or Jan 2020; Premium Audio. (Boyfriend thinks is the issue; Mechanic who glanced it over does not believe it is the issue).

Problem: Fuse 25 Keeps Blowing Within 5 Seconds of Changing Before Starting Truck
Fuse 25: GEM, Speedometer
GEM Functions Affected: Windshield Wipers; Dome Light; 4x4 Low Dash Light; 4x4 High Dash Light; Door Ajar Sensor(?);
Fuse Size: 7.5 Amp
Problem Started: 3/15/2020 (?)

Purchased truck Sept 2017; Odometer stopped working prior to Sept 2018. Have not noticed Door Ajar Sensor Light Since Fuse Blew but have not had passengers since it blew. Dome light did not consistently come on with doors opened but door ajar sensor activated. No dome light since fuse blew. Dome light comes on upon fuse change for under 5 seconds then fuse blows. This is prior to engine starting.

Fuse originally blew while driving (dome light off). Noticed Speedometer was stuck and smelled a slight burning odor. Odor not present on outside of truck. Was almost home when it occurred.
Had truck looked over by mechanic but cannot afford more in depth diagnosis. Mechanic confirmed it is something on that circuit blowing the fuse.

Headliner is dry rotted and has water marks due to possible leak in windshield or back window.

Odor seemed to be coming from dash area.

Other GEM Fuses include 10, 20, 28; none are blowing.

No other electrical issues have been noted.

No known anti theft system installed. If present, is deactivated.

Shifter sticks when shifting gears but has existed since purchase. Daily driver vehicle.

Truck is running with no other issues known observed.

Easiest way to self diagnose and most likely culprit? This is my only vehicle and needed to get to and from work.

State is on 24 hour stay at home order due to Coronavirus. Auto Repair related industries are open. Cannot have company come over to assist due to state mandate nor give me rides. Cannot afford in depth diagnostics or mechanic repair at this time. I'm classified as an essential employee so I have to be able to get to and from work. Please help.

 

Welcome to the forum

Yes, fuse 25, in CAB fuse box, should have power(12v) all the time, its not "key on" power, so would blow quickly as soon as you put a new one in

It powers GEM "timer", also powers speedometer motor in instrument cluster

I would guess best way to attack this would be to pull out the radio to get to GEM wiring first, and you may need to pull out the cluster next

Unplug the GEM wires and use an OHM Meter to test if either of the two wires are shorted to ground, if not then problem is inside GEM module
If there is a short to ground then either the wire is chaffed and shorted or the short is in the cluster/speedometer motor specifically

Diagrams here so you know which wires to test

 

Thank you. I was afraid someone was going to say speedometer component - It was a scent similar to a burnt out alternator or burnt out computer component but relatively quickly dissipated (gone by the next morning). The speedometer was acting a hair goofy right before hand, kinda like it was going nuts. I was going a low speed as I was on a two lane road with a speed limit of 35 and a car going about 20 in front of me, and it just... up and down, not moving up when I accelerated, dropping when I accelerated, going up when I decelerated... really weird but only did it for a moment before it just stopped moving at all and was only moving in increments of 2 to 3 mph. Unfortunately, I've seen that behavior before with computer components that were about to go (imminently).

Admittedly, I've been driving it (no choice). With a manual, I can at least determine my speed via gear and tach reading.

 

That could have been the GEM wire shorting out as well, they are on the same wire

 

I'm just hoping it's an easy fix and easy to find.

I should have been a little more clear on something - when I check computer components, I always check the wiring or connections as a precursor because that's where you should always start. It's one of the top reasons to have a component burn out. Sometimes you can stop a component that's about to go from going if you can catch the reason before it does. Sorry, I don't always use a very logical thinking process so my train of thought can be a little hard to follow . I also have a bad habit of forgetting to write details during that thought process. The fuse blowing would have had a protective quality by stopping the imminent demise of the speedometer if the wire is shorted. It would have also stopped surges from causing immediate destruction from the GEM if that is what went as well.

I do thank you for giving me a good starting point. I may not know much about auto repair, but I do know a few things about electronics.

I do have a question though... how do I figure out which wire it is if it's blowing the fuse as soon as it's inserted? As soon as the fuse blows, there's no power going to the wires. I could do a little trick with a wire that is used to check PSU's in a desktop computer, but that would risk a fire if that wire got too hot, wherever it may be.

 

Never mind, I'm tired and had a stressful day. My bad. Brain fart. LOL

 

Thats what the OHM meter is for

A 12volt wire should not be connected to Ground(metal of vehicle), fuse 25 is connected to ground so it blows

So touch OHM meter probe to bare metal, like a screw, and to one of the fuse 25 wires at the GEM, if it shows low OHMs then its still shorted

You unplug the GEMs 2 fuse 25 wires and then test them, if there is still low OHMs then short is most likely at the cluster
If OHMs are high then short is in the GEM
You can test each of those 2 GEM connectors to see which one is grounded inside, not that it matters because you probably can't fix it and would have to replace it


There is no "trick" in using a larger fuse, i.e. a wire in place of a fuse, that's just 'nuts', a technical term, lol, so don't do that

Volt/ohm meters are cheap and will save you lots of money down the road

A fuse is just a smaller wire than the wire it is protecting or the wires in the component being powered, so if there is a short and AMPs get high the smaller wire heats up faster and melts breaking the connection before the larger wire does, so simple as that
If you put in a larger fuse then the wire is no longer protected, and it HEATS UP, or the component does, and all the 'magic smoke' comes out, which is very very hard to get back in

 

Yeah, I realized that, that's why I said brain fart LOL. Long day like I said. Thank you though, that additional information will be very helpful!

 

Sorry was on the phone when I was writing the post and didn't see your other "brain fart" post come in

 

It's fine! You actually provided some more information that will be very helpful! Thank you so much!

Vehicles aren't my expertise! They're yours from what I've read on here!

My expertise revolves around computers and horticultural sciences. :-)

All of the information you have given has been incredibly helpful in helping me figure out where to begin and how to determine what direction to go in once I do begin.

 

Oh this is gonna make some people laugh.

I know more or less what wire it almost beyond a reasonable doubt without getting into my dash or running tests.

I got my truck back from the mechanic who couldn't diagnose the problem with a cursory glance. They confirmed it keeps blowing the fuse but that was it. So I picked it up and was trying to get my hands on a Multimeter.

I ended up having to run out to get some prescriptions, and noticed my 4x4 lights came on for their self test. Wait, what? I ain't see those since the fuse started blowing.

Ok, so I drive to the pharmacy, notice I still have no speedometer. Again, my truck is a manual so while legally important, I can determine my speed easily enough via tach and gear.

I get home and decide to basically put the cover back on and see if there was a fuse in the slot (cover was sitting between the seats). I open the door with my keys in the ignition and... dingdingdingdingding. Ain't heard that in awhile but it doesn't always go off, but when I glanced over to grab the cover, I stopped.

Dome light was on.

Wait... that was shutting off as soon as the fuse blew... I turn the ignition and flip the **** for the wipers... I have wipers... The fuse isn't blown....

But I don't have a speedometer. It means it was something with the speedometer wiring or another electrical component of it. If there's another fuse within the speedometer itself, that could have blown but I honestly don't know if there is or not. I'm not getting an odor from it either. As soon as I get the chance, I'll look at the wiring and stuff. Originally, i thought it might've been something with the speedometer but wasn't 100% sure.

Like damn... my truck helped me figure out what was wrong with her again LOL

 

I'm a little lost here, you said the fuse blew as soon as you out it in place.

How are the dome light and the dinger on ?

 

It was. I took it into a mechanic and it kept blowing on them too, but I couldn't afford any in depth diagnostics ($300 even after I told them I thought it was the speedometer or a wire to the speedometer), so I went back and picked it back up. I'm guessing the last fuse they placed didn't blow because an internal fuse in the speedometer itself blew if there is one, or the wire fried itself so much that it stopped blowing. Not really sure which but that fuse has to be intact for everything to work. I'm afraid to remove it to check it though. I did look at the size, it's the right one. That said, this isn't the first time my truck has fixed itself or fixed itself enough to tell me where the issue is when there has been one.

It's either that or they fixed it a little but not all the way, thinking on swindling me into paying for more work. I just bought tires - they said I needed tires. They said I had a coolant leak - already addressed last year and I've checked it a few times; it's low but only because I haven't put fluid in since the thermostat was changed over a year ago and it's only low in the reserve tank but not that low. I know my windshield washer fluid reservoir is empty - I haven't gotten around to filling it back up. They said I had an oil leak - I just had an oil change done at which time that leak was sourced to the o ring around my drain plug. No leaks since and all other seals but one have been replaced, with the only one not changed being checked often. They also claimed my trans was leaking (no, it was oil blowing back onto the trans from the drain plug), and they claimed my power steering fluid was burnt up (I checked it a few days prior and it was fine). My front brakes were changed about a year and a half ago and shouldn't be due either but they said they were dangerously low. I do maybe 5k miles a year in driving and they aren't rubbing. My stepdad changed them with me there watching, trying to learn to do it myself... and they claimed I needed a new battery. The battery is brand new.

Needless to say, I am not going back to that mechanic ever again even though they are a 'top rated mechanic' in the area.

 

No, there is no fuse for the speedometer motor

Fuse 25 not working shouldn't have disabled the GEM, its for its timer circuit, so has power all the time
It would disable speedometer

I do not have an internal wiring schematic for a GEM, nor do I want one, lol, but if timer is disabled GEM may or may not "wake up" when a door is opened or key fob used
The GEM is suppose to "go to sleep" after 20-30minutes of Key OFF/Doors Closed, and also shut off Battery Saver relay which disconnects all interior lights so battery won't be drained
Key on the dome light should work when door is opened

If this timer is disabled then GEM may be staying on, and that will drain the battery, but would take a few days