Amps keep shutting off

Does it happen randomly, like when you hit a bump, or after they have been playing a while and you can almost set your watch by it?  Do both amps turn off at the same time every time?  Do they both come back on by themselves or do you have to cycle the power?

If it happens randomly, you may have something as simple as a loose ground connection.  If it is after operation, it is probably heat-related and the amps are going into protection.  This is what the red light means.  Maybe  your gains are too high or your speaker impedence load too low.  If both amps go off at the same time every time, it may be related to a bad power or ground, or to problems in your head unit or RCAs.

Lots to check out.  Can you give us some more info about the problem?

So the problem did not start until you started adjusting the gains?  Sounds like you have the gains too high.  If the system was installed properly to begin with, why did you feel the gains needed adjustment?

Remember, gains (AKA input level controls) are NOT volume controls, they are input sensitivity adjustments.  They need to match the voltage input coming to the amps.  Set them too "high" and you will exoperience clipping.  WAY too high and you may experience such severe clipping that it can destroy your speakers (not too likely in subs, but much more likely in the full-ranges) and you may be "bottoming out" the speakers (driving the voice coils against the mechanical stops.)  This can cause amps to shut down in protection mode due to over current draw, and can fry a voice coil if the power rating is too close to the max the amp can put out.  You say the gains were set to 75% when you began?  This is very high indeed, and you must be sending them a low voltage signal.

For example, y head unit puts out 7 volts in the pre-outs, which means the gains on my amps are set to near minimum and they are still capable of 100% power output....

I suggest turning the gains DOWN and then re-set them properly.  See if the problem goes away with the gains set correctly.  If you don't understand the proper method for setting gains, let us know or do a search as there are several methods and many suggestions in this forum.

Assuming you think you have the gains set properly, first determine if your amps are defective.

Disconnect all speakers and power on the system.   Turn up the volume on the head unti to the point where the amps normally shut down.  Watch them and see if they go into protection.  If so, your problem is either defective amps, a defective head unit or a corrupt signal between the head unit and the amps.

If the amps just sit there and all is well, turn the system off and re-connect the speakers one at a time.  Turn the system up and wait to see if the amp shuts down.  When it does, you either have a bad amp or a bad speaker or a bad connection to that speaker.  If no ONE speaker can cause the problem, but if you connect more than one ind it happens, you have an incorrect speaker wiring problem causing too low an impedence.

Go slowly and be methodical and don't try to rush.  Troubleshoot the system until you have things narrowed down.

I still think that since BOTH your amps are going into protection, you either have a horribly low impedence load on them or you are over-driving them with either too hot an input or too high gain settings.  They are shuuting down in protection from excessive heat.

It is hard to say what could be causing the amps to shut-down.  Start by checking the wiring and the fuses.  A lose fuse could cause one amp to go out and when it attempts to come back on the instant current draw would cause the other amp to shut down due to lack of power causing one or both amps to shut down simataneously or at the same time.  If the amps are confined to an area where there is a lack of airflow the amps could also be overheating which would cause them to shut down.

If all of the wiring checks out there could be a bad set of speakers somewhere.  But since both amps are cutting off it sounds like your friend has a wiring issue some where.  Check the radio wiring it could be a lose wire somewhere.