The "safe mode" on your amp usually kicks in for two reasons - the ohm load on the sub is too low for the amp (presenting a "short" to the amp), or it's going into thermal protection because the amp is too hot. From your description, it sounds like there's a short in the wire, the sub's ohm load is too low, or the sub is partially blown.
If you have another sub or speaker, connect it to the amp's output and see if the amp still goes into protection mode. If the amp goes into protection with a known-good speaker, then there may be something wrong with the amp's power supplies. If the amp works properly with another speaker or sub, then I would check the sub that's causing it to short out.
You may also want to check whether or not the amp is over heating by just touching the amp when it goes into protection. If it's just warm, that should be ok - if it's hot, then it might be working too hard. In this case, you may need to check the input voltage (12-14VDC) and the size of the power and ground cables. If your ground isn't properly connected, it can cause weird problems like over heating, shorts, erratic behavior, etc...
Answers & Comments
The "safe mode" on your amp usually kicks in for two reasons - the ohm load on the sub is too low for the amp (presenting a "short" to the amp), or it's going into thermal protection because the amp is too hot. From your description, it sounds like there's a short in the wire, the sub's ohm load is too low, or the sub is partially blown.
If you have another sub or speaker, connect it to the amp's output and see if the amp still goes into protection mode. If the amp goes into protection with a known-good speaker, then there may be something wrong with the amp's power supplies. If the amp works properly with another speaker or sub, then I would check the sub that's causing it to short out.
You may also want to check whether or not the amp is over heating by just touching the amp when it goes into protection. If it's just warm, that should be ok - if it's hot, then it might be working too hard. In this case, you may need to check the input voltage (12-14VDC) and the size of the power and ground cables. If your ground isn't properly connected, it can cause weird problems like over heating, shorts, erratic behavior, etc...