Hey ! First time on this thread.I have a 97 4 Runner 3.4 SR5 Automatic. Iam having a issue with my

10amp gauge first blowing ,knock out my gauges,power windows,reverse lights,blower motor,a/c,no heat.at first it was blow every time you turn the switch on. I’ve replace the fuse box, the one at the steering wheel,a new alternator &disconect the towing harness.since I put another fuse box in, the fuse doesn’t blow that much.I can at least drive 10 or 15 miles before it blows again.I ck the harness connection & wiggle them, but haven’t found anything wrong.since my 4 Runner been sitting in my driveway & me checking everything my CEL came on , scan it & code po300 random misfire & cyl 5&6 misfire.I ck my connection couldn’t find anything wrong.clear codes light never come back on, test drove it feel a slight miss accelerating at 35 to 40 miles per hour. Haven’t had no issues with the vehicle , theses two rings pop up at the same time. Has anybody had this problem or no what I can ck.

 

You need to fix the electrical issue because that could cause a bunch of other issues. Replacing random parts won't get you there. From your description, fuse boxes and alternators are the last thing I would think of.

You need to know what devices participate on that 10A circuit and test out each one. Find a factory wiring diagram either online or a PDF download from ebay.

WHAT switch triggers the blown fuse? You weren't clear. Does it still blow randomly without activating the switch?

Disconnect ALL aftermarket devices. Aftermarket security and alarm systems tie into everything and always cause problems.

After you fix the electrical issue, you can try some stuff to narrow down a general misfire if you still have it:

Pull the plugs and see if you see any issues. Plugs often tell the story. Are they black or oily? Grey? Worn? Not OEM? https://www.championautoparts.com/P...-and-maintenance/how-to-read-spark-plugs.html

If it was a coil pack, 3 and 6 or 2 and 5 would probably fail together. Since you have 5 and 6 misfiring...makes me think someone didn't want to change the rear spark plugs. So yeah, pull the plugs and take a look.

Plugs and wires should be changed at least every 150k miles. Coil packs don't usually go bad. Only use TOYOTA or TOYOTA supplier parts.

Do a leak down\compression test. If you have bad compression, you'll get misfires.

Can also be a weakening fuel pump or a bad fuel regulator. Do a fuel pressure test. Replace pump with TOYOTA or DENSO pump only.

 

Welcome from Arizona!

 

Check your ground. Doesn't sound like a ground issue to me, but they can cause all sorts of problems and it's easy to check.

 

Usually a fuse blowing is too much ground

 

Welcome to the forum.