Direct module replacement for viper 300+

What would directly replace the brain without changing the harness? I notice I can't hook a range antenna I have without cutting it and hardwiring it to the alarm wire and a ground

not sure what you mean but as far back as i can remember all DEI brains use the same main 12 wire harness and so do the new ones

What I'm trying to say is that I might want to upgrade my alarm system. But by doing so, I'v like to keep the same 12 wire harness as you had mentioned. I have looked at some of Vipers top end models and they seem to ahve another harness. Is it even worth upgrading from a 300+?

Your alarm (Viper 300+) and a higher model (Viper 790VX) both use the same 12 wire harness (except in the 790 the yellow isnt used, im guessing it gets the 12 volt switched from the other harness) but it also uses the same 3 wire lock/unlock, there are a few changes here and there with each alarm but its pretty much the same 12 wire harness, the higher alarms have a few more connectors than the lower alarms (more options) but they all still use the 12 wire harness -Chad

Racingtoys is pretty much right. But! It depends how old your 300+ is. If its old enough that yer transmitters have a red led on them, then the harness is different. But if yer transmitters have green lights on them, then the harness is the same as pretty much every newer dei alarm. Both the old style(red led) and the newer style(green led) use a 12 wire harness, but the the older ones have a different plug, which wont plug into the newer ones. But if you do decide to upgrade to a newer alarm, all the wire colors will be the same, so it will be a piece of cake to just cut and butt connect the same color wires.

no problem, man