2004 GMC Envoy- RAP/ amp cutting out

Sorry for the long post, but this isn't a straight-forward problem. I don't know if I'm having one or both of these two problems: 1) GM Class 2 Data Bus with Retained Accessory Power(RAP), 2) wiring or needing a capacitor. Here goes:

2004 GMC Envoy SLT, nonBose, has OnStar, in-dash AM/FM/6-CD changer.

I'm keeping the factory radio but adding a 4-channel amp using a PAC AOEM-GM24 (basically an OEM-1). This interface isn't listed as the correct one for my vehicle, but I checked with PAC before buying it. It does work for my vehicle because it's nonBose. I do have all four channels getting from the radio to the amp, so the interface is working with my radio and amp.

I've had the usual GM Class 2 Data Bus problems I had when install a SkyFi tuner: 1) The vehicle doesn't have an accessory wire. 2) The brown wire and the pink wire under steering column do not give Remote Accessory Power (RAP) as advertised all over the internet, 3) The radio doesn't have a power antenna lead or an amp trigger lead to tap into.

I'm currently using the front windshield wiper fuse in the fuse block under the 2nd-row seat to get a RAP power source to the AOEM-GM24 unit to turn on the amp. This works. Problem is, when the windshield wiper first turns on the amp cuts out (no sound from any speaker) for a split second. There's no pop afterward so I don't believe the amp is actually turning off and back on again. Once the wiper motor is running continuously there isn't a problem- just when it first turns on.

It isn't just the loads on this one fuse/circuit that are causing the problem, though. The same thing happens at the instant I step on the brake. If I keep my foot on the brake the amp works after the initial cut-out. The brakes don't have anything to do with RAP or the windshield wiper circuit, as far as I know. They've got their own fuse(s) and they work even if the key is never turned to the "Accessory" (not  really the correct word for a Class 2 Data Bus)  or "Run" positions.

Why is the amp cutting out?

Maybe the problem is a voltage drop in the wiper motor circuit when the wiper motor first start drawing current. I've thought of installing a SPST relay, using the windshield wiper fuse for the "signal" and a battery-source fuse for the "load." This way the wiper motor circuit could have a drop in voltage but the PAC interface wouldn't see it- the wire going to it would be getting its current from a different circuit. This doesn't explain why the amp is cutting out when I step on the brakes, though.

I think I'm OK with wiring issues: Amp power lead- 20-foot long, 4 gauge. I didn't see a good way to connect the power lead's ring terminal to the battery's side-terminal connector so I connected it at the under-hood fuse block that's connected directly to the battery by a wire about 8 inches long. Amp ground wire- 4 gauge, about 15 inches long, bolted directly to the vehicle frame. Signal wires- (Fuse-to-Interface and Interface-to-Amp) Both are 16 gauge and about 16 feet long. Speaker wires- All four are 12 gauge. Front are 16 feet long, back are 8 feet long.  Vehicle Electrical- OEM battery and alternator. No known previous battery/alternator problems, nothing added to vehicle to tax the electrical system other than the amp.

I've thought about adding a capacitor for the signal circuit going from the fuse to the interface. My understanding is that a capacitor is usually used to maintain a constant current for an amp that's running subwoofers. Could a capacitor also be used to maintain a constant voltage? I haven't been able to measure for a voltage drop in the signal circuit yet today, but I can't think of anything else that could be causing this problem.

I've emailed PAC today about this problem. I assume they're closed on weekends. I asked if a TR-4 module has the same problem with obtaining an RAP source that the AOEM-GM24 does. I imagine any  device is going to have to have an RAP-enabled source attached to it in order to keep the amp running as long as the radio is. I doubt the TR-4 can divine the status of the ignition switch, status of the doors, and count for 10 minutes any better than any other device. When they answer I'll post any suggestions they have. Anybody have any ideas in the meantime? Thanks.

I think you're right. The more I think about it, if there was a problem with voltage drop in the signal circuit, the amp would be turning off and back on. The cut-out is too short for that. I started thinking about that power wire a few hours after I started this thread. Tomorrow I'll try to attach directly to the battery. I thought about placing the ring terminal beneath the positive cable. There's a large rubber boot around the screw that holds the wire to the side terminal. I am fused, by the way. I hadn't mentioned that. The install kit I bought came with an 80 amp fuse. My amp has two 30 watt fuses. Thanks for the advice.

Now I've got to find a solution for the RAP. My amp's signal wire currently comes off the windshield wiper fuse. I thought it worked when I was checking voltage on it the other night. Guess not. The amp shut off when I turned off the key today. Now if I could just find a RAP source....

Update:

I've connected the 4 gauge power wire directly to the side terminal of the battery. I had to trim away some of the red plastic around the terminal bolt to do it. I've also double-checked the ground: 4 gauge wire bolted directly to the frame. Ring terminal directly contacts bare metal (no paint, grease, dirt, etc.). I don't feel I have a problem with power to or ground from the amp.

The amp is still cutting out when I step on the brake or use the turn indicator. This occurs with headlights and AC on or off, in any combination. No other electrical add-on other than a 4-channel amp rated 80 WRMS at 4 ohms. Using 4 ohm speakers, one speaker per channel. No bridging, tri-mode. No sub.

I connected a voltmeter to the connector for the rear windshield wiper switch on the front console. I noticed a slight deflection in voltage (less than 1/2 volt) when the brakes or turn indicator were used. This was again at low stereo volume, no headlights, basically shouldn't be stressing the car's electrical system.

Is it normal to have this dip in voltage? Can I do anything to either eliminate the drop in voltage or somehow maintain a constant voltage to the remote input on the amp so that it doesn't see this drop?

Hopefully fixing this will not require doing something like getting a new alternator. I would hope this system would be able to tolerate what I consider to be a SMALL amp without an alternator upgrade.

By using this line, you may be overloading the electrical circuit, as most of your newer vehicles use one circuit for more than one source. It is possible that whenever you turn on your lights/windshield wipers/etc. that your amplifier is sensing the quick reduction of power and sending it into temporary protection ofr simply causing it to shut off.

The best and easiest solution is to find another source to eliminate this and also the potential problems this may cause from stressing the electrical circuit.