It doesn't really sound as though you have the premium sound in the truck at
present. You probably do not need a custom install. BUT, there is a way that
you can find out. You DO need the harness, unless of course you want to cut
out the existing plug. Once you have your harness plug it in without it
being hooked to the stereo. Then you need a 9vt battery, take your speaker
leads off the harness + and - to each speaker, touch these leads to the 9vt,
you should hear a pop and static at each speaker location. As long as you
hear this sound you have no amp. If you do not hear this sound then you
would need to run speaker wires to your present speaker locations, this
translates into alot of work. You have to remove mouldings ETC. It's really
not that hard just takes awhile. I had to do it with my 4 Runner. I assume
that you have speakers in the doors and the rear somewhere. The doors will
be the hardest to run as you have to remove the door panels and run the
wires thru the door jam and into the door. Putting in a stereo is not hard
even if you have to cut the factory harness, all there is is a hot (b+)
(RED) a common (-)(ground, BLACK) and an ignition hot(+)(YELLOW). Then you
have the speaker wires. Unless you are installing an aftermarket amp, then
you will have to hook up the blue wire off the stereo (REMOTE).THe orange is
for the power ant if you have one. These colors are usually standard, but
you will have a wiring diagram with the stereo.
If you have any questions feel free to email me. I can help you out.

Searcher (1986 sound challenge 1100 watt class winner) IASCA
Yeah its been awhile since I was into the boom cars but I still keep my paws
in the loop, I am no longer into the BOOM but I do like HIGH quality sound.
and by the way a Pioneer head unit has been my top pick since 86, I have
never had anything else win in my cars. I run a Pioneer 6700 with Infinity
reference seps. Getting ready to hook it all into a Rockford Fosgate Punch
amp.

goodluck

If you have the upgraded system with the "amp" there are two ways to
add an aftermarket head.  The easiest is to be a harness you put right
behind the head  that converts the new heads speaker output voltage
DOWN to the lower voltage level the amp needs for its input.  That's
how I did my 92.  As I recall, it included an adjustment for volume.
It worked but I was not thrilled with it as even with it set for
highest volume it still wasn't as loud as I thought it should get.
Plus it seemed to introduce a small amount of distortion.

The second way it to find the amp and take it out of the circuit. I've
heard that for the early explorers there is a harness you can buy that
makes bypassing the amp, once you find it and can get to it, a plug
and play.   If you can't find a harness you could just figure out
which wires from the front going into the amp need to be hooked to the
wires going out of the amp.  

Some people have just said "screw it" and run all new speaker wires
from the new head.  To me that sounds like more work then bypassing
the amp.

Thanks for the replies.

I found another stereo shop who had the adapter harness.  I spliced it
in and everything is great.

2nd opinions ( or 3rd or 4th ) can be very valuable.

Thanks again

Dave