Here's the description.
The radio will not play when the key is in the acc position.
When many accessories(heater fan, seat heater, windshield wipers) are turned on when the car is running the radio will cut off.
At a stop sign when the car is turning less rpm's the radio will cut off and the dash lighted up Christmas tree style.

I was thinking it may be the battery, but the car starts fine every time. The lights are very bright and do not cut off when the car is turned off. It probably isn't the alternator because the battery stays charged and the system runs pretty good unless nearly all of the accessories are turned on at the same time. I'll probably take the car to autozone and have them test the battery and alternator first just to be sure.

I'm thinking maybe a loose connection or a bad ground somewhere.

Anyone have this problem before?

 

It sounds like you need to have a load test performed on your alternator. Just because the battery is being kept charged doesn't mean the alternator is not the culprit. It's a good place to start in any case. It could also be a grounding issue like you mentioned, or a loose connection at the ground/body connection point.

 

I kind off discounted the alternator because it doesn't play a role when the car is off and the key is in the acc position, or I don't think it does.

 

Maybe it has that well-known problem with that wiring loom in the luggage compartment?

 

I thought that might be the problem because the dash light comes on occasionally. The amber one with the rear lights. I removed the wire harness from the trunk lid arm because it was pinched some. I looked at the wires and they appeared to be okay. I haven't tested with an ohm meter though.

 

There are two points whee the wires are bent 180*. One is on the hinge and the other is near the sub amp. I removed the tape and the wires were in good condition. I tested the wires they seemed fine. I cut the bent parts out of the wire and used butt connectors to reconnect.

The light went out on the dash and the radio hasn't cut out anymore. I guess the rear wire loom problem is a fix all even if the wires are not broken.

 

Wow, it sounds like that wiring loom is a nasty little booger. I have never even paid any attention to that area on either of my LS400s. Exactly where is this trouble area located? Right at the hinge?

 

Not sure which point was the problem on my car since I cut out both sections at the same time.

 

Thanks for the photo of the exact spot! Wow, in that area, its no wonder there were issues. Looks like the wires could get pinched! Was this photo after you moved the wires around?

 

theres also a tutorial on how to fix it on lexls.com

 

The picture was after I moved the wires on the hinge, but not the wires near the amp.

 

I see.

Well, here is a photo of the trunk wiring loom on my 91' LS400. I cannot tell if its been tampered with / modified yet or not......

 

That is not factory. It doesn't look like mine did anyway and I know mine was factory. The tie wrap and sloppy electrical tape give it away.

 

I think I may also have a photo of this area on my old 1990 LS400. I think it was factory, which was amazing, since it had 252K and no electrical problem.