Is it the head unit or the built in amp?

[buzzhazzard]

Hi All,

I'm a new guy here.

I have a 1998 Expedition XLT with the Premium sound system. Years ago, I replaced the stock head unit with a Sony CD AM/FM head unit. Recently, I have been having sound issues. The speaker volumes independently fade in or out in various speakers for no rhyme or reason. The left front might sound good but the right front is much lower. Then a few minutes later they sound the same, and then later it's another speaker.

I have checked all the physical connections at the speakers and the head unit and they are sound.

I was going to replace the head unit with something more modern, but during the research learned that between the head unit and the speakers, there is apparently a stock amplifier, so now I am thinking it could also be the factory amp.

So based on the symptoms I described earlier, does anyone have any best guesses on whether the issue is the factory amp or the head unit? I've read that the amp can be a bear to change out, so if it's the amp, I'll be back for more help there.

Thanks in advance.

 

[Canadian Expy]

The only ampI know of is in the MACH audio system, and it is only for the sub in the rear. Which is where the amp is located.

 

[1955moose]

I agree with Canadian expy, I've got a 2000 expy Eddie Bauer with stock mach stereo. I've also heard that only the 8inch rear sub has a 35 wpc amp. The stock head unit just has the basic 15 watt built in amp. Do you still have the stock stereo you can swap just to see. You said all connection were good? How about grounds? These trucks are famous for ground problems. You might try a separate ground wire, hook it to sony's ground see if it improves. It's cheap and easy to try. Keep us posted!


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[buzzhazzard]

Thanks for the replies. After doing a lot of searching, the one thing that is clear is that there is confusion on this topic. The MACH systems do have amps located behind the third seat, but the Premium systems ALSO have an amp (albeit a small 4x20 one) to power the main speakers. The original head unit is probably quite low in power and the Premium simply boosts the power a bit.

For those who may benefit from my experience, read on.

The amplifier is located behind and below the head unit, and though it's a bit of a chore to remove it, it's not too bad. In fact, if your goal is to simply bypass it, you don't have to remove it at all. I decided to pull it and leave the empty space in the event I want to add another amp someday.

To access the wire harnesses to bypass them, remove the "instrument panel floor duct panel." This is the black plastic panel located between the dash and the carpet directly below the radio. It is held on by a push clip on each side and an expander clip in the middle. Gently pull these loose and set the panel aside.

NOTE: I don't have one, but if you have the center console assembly, you will probably have to remove that as well.

Once removed, contort yourself so that you locate two wire harnesses located on the bottom of the amp. Carefully remove them from the amp. I just ordered a Metra 70-5513 wirin harness for about $12 and my project is on hold until it comes in, but this harness should be the one needed to connect the two wiring harnesses together, which bypasses the amp. [EDIT: The 70-5513 did not fit. Instead, I used a 70-5605. That worked great. See my follow on response to Leo below.]

At this point, your head unit should be able to power the speakers.

Why do this? If you are replacing your OEM head unit with a nice new unit, it is, by design, capable of driving the speakers without this OEM amp. Why would you want to leave the original amp in place? In can only degrade the sound of a superior system.

For those who want to physically remove the amp as I did, read on further.

Remove the head unit (PM me if you don't know how to do this). Then remove the two screws holding the climate controls. You will see the silver colored amp. It is held in by three bolts, each with a 7mm head. The top bolt is visible behind the climate controls.

The bottom two bolts are a little trickier. They are located under the bottom of the dash (after you have removed the instrument panel floor duct panel described above). As you are sitting in the seat, the bolt points face you, so reach under the dash below the amp and locate them. Remove them with a 7mm open end or box end wrench. I have attached a pic that I took by placing my phone below the dash to see the bolt. If not previously accomplished, remove the two wiring harnesses. There MAY be an unrelated harness fastened to a hole on the amp bracket. If so, detach it too.

If you have gone this far, you are close, but the hard part is dropping the amp through the opening at the bottom of the dash. It's a tight fit, but it will fit. The tolerances are pretty tight.

Anyway, I hope this helps someone else who may have the same questions I had. I will bypass the amp with the Metra harness and I am also installing a new head unit. It's a '98, but I only have 125k miles on it, so I hope to keep it going for several more years until the kids are out of college. I might as well have some nice sound along the way.

 

[1955moose]

Good to know, years back I had a 89 Lincoln mark 7 that also had a separate amp. I purchased the harness from Crutchfield that eliminated the amp. I was running a pioneer head unit that had its own amp. It cleans up the sound, as you don't want to boost a built in amp. It's kinda like back in the 70's when they sold eq's with amps that boosted original radio amps. They just sounded loud and boomy, some people liked that.


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[Leo's ride]

@ Buzzhazzard -

I'm about to do the same on my Expy Eddie 1998 - Did the Metra 70-5513 work ? please let me know how was the end result of your experiment.

many tks !!!!

 

[buzzhazzard]

@ Buzzhazzard -

I'm about to do the same on my Expy Eddie 1998 - Did the Metra 70-5513 work ? please let me know how was the end result of your experiment.

many tks !!!!

Leo,

I'm glad you asked. The answer is NO, but there is a better solution. I'll edit me earlier post. Thanks for the reminder.

Despite advice from other sources, the 70-5513 only fit one end of the two harnesses at the amplifier, so I returned it and ordered 70-5605 for about $18. That kit consists of two cables, each with a harness on one end and a bare end on the other side. You have to connect them together. I soldered mine and used shrink-wrap. Ironically, Amazon's "part matcher" told me the 5513 would fit and the 5605 would not, and the opposite was true, which at least got me free shipping back on the 5513.

The end result is a cable where one end plugs into to factory speaker harness that originally connected to the output side of the bypassed amp (and goes to the speakers) and the other end plugs into the factory radio--or provides a connection point for a new head unit.

This is actually a better solution than the one I had planned because the 70-5605 is 16 gauge wire, and it replaces the factory wiring that originally went from the head unit to the factory amp input, and those wires appear to be only 18 gauge. So you are upgrading the wiring during the replacement.

I removed my factoey amp (which was a chore) so there was plenty of room to feed the new cable assembly from the head unit to the harness near the bypassed amp, but even without removal, I think you should have plenty of room.


Let us know how it works.

 

[98xlton20s]

I am having the same type of problem wit my 98 expy. Only the back door speakers work, and the passenger side front door speaker phases in and out. I was not sure if this was a connection issue at the speakers or if the amplifier lost two channels. Then i had a new pioneer head unit installed yesterday, and lost all sounds all together. I tapped on the dash and the sound came back. Could this be the amplifier?

 

[Leo's ride]

Hi Buzzhazzard,

Thanks for the feed back .. I've also ordered the 70-5605... I'm many miles away , and would not take the chance , most of the other parts will be arriving in the coming day and I'll probably be set to work on it this weekend.


also found this guide to the Expy Sound system , I hope that it can help others .

http://www.scosche.com/media/guides/fd921.pdf[/

Cheers ...

 

[Leo's ride]

The task was not as easy as I've thought , I have the Eddie Bauer model with a central console , instead of removing the whole console to access the Original Amp , I've been able to reach and disconnect the Amp connector from behind the dashboard (next to the gas pedal ) , was not that easy as the space is very limited but achievable.

The Metra connector kit 70-5605 (although in Amazon it mention into the configurator that this part does not fit the Expy 1998, it does) it provided two harnesses 1) long one to bypass the amp (connect speakers to the new head Unit) and a shorter one to connect power.

The dashboard enclosure is not 2din , I used the Metra 99-5800 dashboard adaptor with pocket . I needed to instal with the pocket down due to the size of the screen on my new headunit , this meant that a small modification need to be done on the headhunt . as it touches the dashboard just a enough to not let it fit well (same applies to 2din headunits).

Also my new head unit is about 5mm wider than the dashboard (!!!), in this way I had to assemble the headunit after putting the dash (air vents) back into place .

My original (Mach door ) speakers are working (the subwoofer is blown) , noticed that the doors speakers are mid to high range only , having the sub woofer blown , the quality of the sound is very bad (no bass) ... Next project is to change the 4 (doors speakers) and the Subwoofer.