Stereo Head Unit Blowing Dome Light Fuse - Stumped

[Nay]

I have read all the related threads I could find and still stumped. Hoping some of the electrical gurus can help! Here's the background of what is happening and what I have tried (1995 FZJ80):

- Last week, turned on the ignition in the morning and noticed the clock , aftermarket mirror dimming mirror, and head unit had no power. It is an aftermarket Pioneer unit that has been installed since 2008;

- Replaced dome light fuse. Stereo would cut in and out a couple of times and then blow again. I could get it to play for a minute or two at the ACC setting, but fuse would blow immediately on ignition;

- Power to the separately powered sub (Kenwood KSC-SW1 mounted in stock location - factory unit is gone) was off except for intermittent moments while the door speakers would play. The sub is separately powered by direct battery feed with RCA cables and the SW wire from the HU;

- Disconnected the sub at the subwoofer unit connections. No change;

- Bought a new Kenwood HU as I wanted the Bluetooth upgrade anyway. Installed with the supplied Metra harness (Crutchfield). No change - still blowing fuses. Reinstalled old HU since I now had a test harness to butcher (the adapter harness, not factory) in testing;

- Ran a ground wire separately to the engine bay, bypassing the harness. No change;

- Left the rear door speaker harness unattached to rule out door speaker wire. No change, but the system would play longer before cutting out and rebooting;

- Cut and isolated the passenger side speaker wires, so only driver's side door would play. HU would go a couple of minutes before the problem resurfaced;

- Reconnected the passenger side front and cut and isolated the driver's side front. Same result, except I figured out that at low volume with one speaker only that it would play continuously unless I turned volume to about 30, and then it would start glitching. Turn volume back down and it is fine;

- Cleaned all wire to battery connections with acid removing foam, replaced fusible links, installed backup battery. No change;

- Uninstalled old aftermarket heated wipers that were not powered on the dome light circuit. No change;

- Disconnected dimming mirror. No change. Uninstalled mirror at the power tap (see pic below - gray wire). No change, so reinstalled mirror.

So it seems like the system cannot hold any power output. It's not the HU. I have isolated all of the speaker harness connections and the ground. The one thing I have not done is isolate ACC/IGN power (yellow wire) or Memory power (red wire) from the harness.

There is no visible damage to any wires that I can see. The ScanGauge II reads proper voltage from the charging system. I did not install anything new, and the mirror has been wired in since 2008 as well.

I appreciate any thoughts. If it sounds like the power feed to the HU, I can test that and if confirmed would appreciate input on where to rewire outside of the harness, but I'm sick of the trial and error and hope somebody can diagnose based on what I have outlined so far. Thanks!

 

[landcrshr]

The "DOME" fuse circuit is what powers the HU's amplifier, so it would seem as though you have a speaker/impedance issue.

What are you running for speakers?
Is the factory amplifier removed/unplugged?
How and where did you isolate the door speaker wiring?
Which Metra harness?

 

[Oscar Witte]

I agree with crusher. If you are wired using the factory amp it sounds (no pun intended) like that the amp has stopped working. That causes the HU to draw tons of power to power the sleakers. Another test would be to play something through the speakers and see how hot the back of the HU gets.

 

[baselfish]

indeed my first though was that the factory amp needs to be unplugged.....

are you using the metra double harness or the single ?
cruthfield supplied me with the single harness - with RCA plugs -

which I scrapped for the double (Metra 70-1761)

bf

 

[Nay]

Factory amp is completely disconnected, as are the tweeters. The replacement sub is not wired through the factory stuff. The door speakers are aftermarket Kennwood, but the PO installed them. I replaced the factory HU.

The Metra harness is the double, with the smaller just powering the rear speakers (purple and green wires). I don't know what the existing harness model was, the new one is 70-1761.

In terms of door wiring, I just a) didn't plug in the rear door speaker harness, and then b) cut the wires to each front door individually to see if any speaker seemed an obvious problem, i.e. it worked with the passenger front not wired. I did remove a rear speaker relatively recently in order to fix a window track issue, but had no problems after reinstall and the problem is there when the rear speaker harness is disconnected.

A good point here that I forgot to mention. Back of the HU is getting hot when I can keep it running.

Keep in mind nothing is new here, except blowing the fuse. This system has been in place for 7 years. The new HU is sitting on my desk while I use the old one for diagnostics.

Thanks for the quick replies.

 

[Nay]

Here is the new Metra. Old one was the same thing, just different plug to the back of the HU. The orphaned blue/white wire is the out to the Kenwood sub.

 

[Oscar Witte]

The only thing that makes sense to me is that the amp in the HU is not working properly or there is a short somewhere...

 

[Nay]

Right, and I have two HU's doing the exact same thing which rules out the HU amp. I had thought it was the HU...until I wired up the new one...and it immediately blinked...

But where is the short? I've alternately disconnected everything but the two wiring harness power wires (yellow and red). The symptoms never change. So one of those wires? And what then would I reroute to since I can't use a live battery feed?

I really appreciate the inputs here...

 

[ChaseTruck]

I have read all the related threads I could find and still stumped. ...

Put the old swampers back on. The truck needs the vibes to be right...

 

[Nay]

That occurred to me . But it went while the swampers were still rumbling away...

 

[ChaseTruck]

That occurred to me . But it went while the swampers were still rumbling away...

That's too bad - unfortunately, it means chasing electrons...

 

[Oscar Witte]

Does the new HU produce the same amount of watts as the old one? Also have you tried wiring through the factory amp? And how did you run your sub?

 

[Nay]

The old HU is a Pioneer DEH-P3000IB and the new is a Kenwood KDC-BT562U. Both are 50Wx4. Both have a subwoofer out power control (that blue/white wire) and RCA jacks for external subs/speaker expansion. I haven't tried wiring through the factory amp...

The sub is self powered (Kenwood KSC-SW1 - the current version would be KSC-SW11) and is wired directly to the battery for power, connected to the HU via RCA jacks and the control wire. I initially wired the sub to the factory power, but it wasn't sufficient. I need to look up my thread on that install here as it was a fit in the stock location.

Edit: I have idea how to link to my old post, but it's "Stock Location Mounted Powered Subwoofer (Bolt On) and New a Stereo".

 

[Oscar Witte]

I'm sorry man, this is out of my knowledge... Hopefully some other electrical gurus can help.

 

[landcrshr]

I would say it's likely the speakers. Have you tried testing it with only the rear speakers?

 

[Nay]

I haven't - I'll give that a shot as that is one config I haven't tried.

 

[wearsabrowncoat]

I suspect wiring to front speakers as well.

 

[LandCruisinMy93]

My HU had a similar issue of blowing fuses constantly, mine is a 93. The problem is that there are several things running off the same tiny 10 amp fuze. Done lights, clock, I believe some dash accessories and the HU, just way too much for modern HU's. Most modern HU's produce x amount of amps per speaker output, substantially higher than factory HU, so modern HU's draw more juice. As for your HU getting hot, chances are your speakers are a different impedance than what your HU is designed for, did this years ago when I was a young kid in high school wanting a bumping system, didn't know you had to match stereo components of wire speakers a certain way to be useable with a particular HU or amp. What is happening internally is that your MOSFET's are overloaded and working against too much resistance and in the end they'll blow and you'll have worthless equipment unless you can unsolder and solder in new ones. So long story short, check the impedance or "ohms" of the speakers you're running and check the specs on your HU to make sure you're okay to run the speakers you're running. If everything pans out then you may need to run a higher amp rated fuze.

 

[Squash]

Because the HU was intalled by PO my thoughts for you are below.
Do you have a "new" harness with a single blue wire beside a double looped back blue from picture on right side of photo.
Did you tie in the power ant.?
Cut the looped blue wire and see if the unit cools down. You can always resplice.
Wish I'd taken a picture of mine. Needless to say prior to cutting the looped blue wire my HU was noticeably warm, blue the fuse and then required a boost.

 

[Nay]

I installed the Pioneer HU that I'm going to replace since I bought a new HU. The PO installed the door speakers with the factory HU. I never checked the HU to speaker impedance when I put in the new HU.

I do have the looped blue wire on the new harness and I am not tying in the power antenna.