2000 Tacoma Mysterious Electrical Issue

Greetings,
My mechanic whose skill and integrity I trust has not been able to resolve this problem. I am in no way a mechanic so forgive poor descriptions. Sort of grasping for some hope with this post.
2000 Tacoma 4WD, 4 cyl
250K miles

For last 1 week: Fuse for blower fan and gauges (odometer, speedometer) blows when put in reverse. Repeats when fuse is replaced.
Then, intermittently, when start trucks, truck runs very rough, settles to normal, then dies on the road after 5 minutes of driving, or similar variation

Fuse does not blow and all seems normal when reverse mechanism is unplugged.

3 months ago: reverse lamp switch was replaced due to reverse lights not working.Normal function for several months, until now.

2 days ago: Battery found to have shorted cell. Battery replaced. Alternator, starter, battery passed test. Wiggle test done: no issues found.

Issue now the same after work done 2 days ago. Fuse blows regularly when in reverse and reverse mechanism is connected. Intermittently, the truck will run rough then continue to decline as though it has barely enough energy to run, with lights, etc becoming very dim.

Any ideas?

 

What is a "reverse mechanism" ? The transmission?

When that thing is unplugged, does the engine run fine?

Dead battery cell probably has nothing to do with the problem. That happens. How old was the battery? If the new battery dies, there could be an issue, but probably a separate issue.


If the"reverse mechanism" is blowing a fuse, then you likely have a freyed wire in that circuit that has bare wire touching metal and causing the fuse to do it's job.

You're going to have to chase that wire.

I would start by taking the dash apart. Just look for a wire on the same circuit as that fuse. get a wiring diagram if you need to.

 

Chasse the wire from whatever it is you are unplugging on that mechanism

 

Thanks FishaRnekEd; it is the backup switch that it unplugged. Yes, it runs fine when that is unplugged.

 

Sounds like you've already isolated the issue. Test the switch for internal shorts, and replace if required.

 

Thanks tirediron. So you believe the switch could be the cause of BOTH the issues?

 

If I disconnect a component and the problem goes away, it will always be my first starting point. New parts aren't always good parts, especially if they're MiC, 'Dorman' or similar craptastic brands. Make sure you check the harness side of the connector carefully, as the problem could exist there and not actually in the switch unit.

 

Time for a better Mechanic!

If the back up light switch is shorted why has this not been tested? Found shorted or proved in working condition?

The gauge fuse being open can impact the charging circuit which can cause your low voltage and poor running conditions.

 

Much thanks Bivouac, encouraging feedback. What do you mean by "the gauge fuse being open?" And you believe that the back up light switch (OEM) could now be causing this problem, even though it did not cause this problem for the first few months after it was installed? Much thanks.

 

I think he is referring to the fuse being open as in “blown”. Once the fuse blows, the circuit is open and therefore can cause some of the symptoms you are experiencing simply by not being protected by the fuse

 

Got it, thanks.