Will Sanders

Hello everyone,

I installed an aftermarket radio and amplifier in my 2004 ML500 a while back. The audio quality wasn't great so I switched back to the factory setup.

When I was installing the aftermarket amplifier, I cut the speaker wires from the plug going into the original Bose amplifier. I also cut the non-speaker wires from the same plug and insulated them. When I cut the power wire it sparked quite a bit, either on the metal scissors or against another wire being cut at the same time, because I forgot to disconnect the battery. I think that also blew fuse F40 but I can't remember. I wasn't worried about it since I wasn't planning on using the factory amplifier again.

I sold my original radio and amplifier when I started the project so I had to buy new ones when I decided to go back to the factory setup. I also had to reconnect the plug for the Bose amplifier to the original wiring with butt connectors. The new radio turns on and everything appears to be working, but the amplifier does not power on at all. I bought two amplifiers and neither of them work, so it must be a wiring issue.

There are 18 pins going into the amplifier, 6 of which are not speaker wires. At least one of these pins has to be the culprit. Pins 1-3 connect to something called the "sound amplifier module," pin 8 connects to the "CTEL interface," and pins 9 and 26 are for ground and power, respectively. I want to do a continuity test with my multimeter, but I have no idea where to find the "sound amplifier module" or the "CTEL interface." I also don't know how to test if power is getting to pin 26, or if the ground for pin 9 is good.

Fuse F40 looks fine, but I'm worried that the spark from my previous mishap could have messed something up. Any theories? I've been dealing with this problem since AUGUST and I'm pretty tired of not having music in my car.

I would just bring it to a shop and have them figure it out, but I'm having an engine/drivability issue with the same vehicle that I'm putting all of my [hard-earned part-time college job] money into. I don't want to spend more money on the radio than I already have, so I really hope I can fix it myself.

Thanks guys.

Will Sanders

Here are some pictures and multimeter readings I got today...

The following readings were taken with the multimeter set to DC voltage, 20A (see attachment "IMG_1505")

Car off/radio off: 12.24
Car off/radio on: 12.19
ACC on/radio off: 12.01
ACC on/radio on: 11.98
Engine on/radio off: 14.32 (moves around a lot)
Engine on/radio on: No discernible difference (also moves around a lot)

When the radio is turned on the red light flashes from its fiber optic port. No light flashes from the amplifier's fiber optic port. Is there a trigger wire of some kind that tells the amplifier when to turn on?

The other two attachments show the amplifier plugged into the vehicle, and a closeup of the butt connectors, which as I mentioned in my previous post were used to reconnect the amplifier's plug to the vehicle.

EDIT: Not sure why the images are horizontal. They were vertical when I uploaded them.

Will Sanders

Anyone?

Since the voltage seems OK I'm suspecting there needs to be a trigger signal sent to the amplifier for it to turn on. Can anyone confirm which wire is for the trigger?