Very little power from my amp, simple question

[a70eliminator]

Hi, first post here. Have owned my 90 LSC since 1994.
She has the good JBL amp and of course the problematic FM reciever/tape deck.
The original reciever went bad, tape played great but no tuner action so I replaced it with known working unit out of a donor 1992 LSC.
Everything works except for what sounds like very little amp boost, all speakers work, fader, balance, bass, treble, ect.
My question.. Is it possible for the radio to output power through the amp to drive speakers a little bit, like to make the sound of a cheap 5 watt stereo, like as if my amp quit working, like amp fuse blew but radio still somewhat plays without it. It's like 4 degrees outside and I need to check that amp fuse but my hands are froze lol.
Funny thing is the old radio thumped with excellent power on the casette just yesterday, but today with the new exact replacement radio the power is weak FM or cassette doesn't matter.
Also the battery may be weak from tinkering around, could that effect power output from the amp?
Sorry about the long winded post, my buddy has a 5 speed LSC with mustang clutch pedals, he's really into it!

[phoenix]

Hi, and welcome!

When my JBL fuse blew I had no sound, period. I would check (A) the battery - can you start the car and check the radio operation with the motor running? ... (B) if the battery checks out fine, that the connections on the back of the radio are ok. Post back!

[a70eliminator]

Yea thanks man, I kinda figured if the fuse on the amp was blown there would no sound at all but wasn't sure, never had it blow. I was reluctant to even start my baby because it's too cold outside right now, tomorrow it may warm up a little and I'll report what I find. I'm crossing my fingers that it's just low on voltage, maybe getting only 11v or so back to the trunk area, everytime I open the doors all the lights come on and remain so I'm sure the battery voltage is low, been tinkering for a couple days now with this radio issue.

[a70eliminator]

Ok so this morning after charging the battery all night i go out and try again, nothing changed, all works but with limited power, the speakers sound decent at maybe 1/4 volume anything more and distortion happens, I know the amp isn't putting out like it should.
I pulled the head unit out and have it here at work on my desk with a 12 power supply checking the output on the blue wire which by looking at schematic triggers the amp, the blue wire does become 12v hot when radio's power button is pushed so it's back to the drawing board, have to probe for some voltages back at the amp I guess.
It's -4 outside this morning brrrrrr, not going to get much done outside lol.

[a70eliminator]

I don't know, I must be cracking up or something, I plugged the head back in today and it played with the gusto I'm used to! Fed in full bass and treble and volumed up to peak, it sounds clean and sharp thumps bass with no noise distortion, I don't know what I did butt..... I'm happy as a sissy with a (beep) up his (beep)

[phoenix]

Hey man, good to hear you got it fixed. I'm thinking the connections on the back of the unit weren't right the first time. It's really okay, I personally think that speaker plug is weird (I suspect that's the one that was a bit loose).

Enjoy!