Hi yes I read your description fully;-)
The model # ***** be on the main alarm box itself, may be installed under the hood or under one of the seats etc.
But now that I know its a Sidewinder,
I can tell you one thing you can try.
Please disconnect the cars Positive "+" battery terminal for 30 full minutes then you can reconnect that.
This will cause a full system reset, not codes though.
Let me know if this helps, these systems use relays and a microprocessor for controlling the arming/disarming and locks in the system.Sometimes electrical glitches will cause this problem,that would be the cure if that is all it is that happened.
But since this was a police car, the system may have been wired this way for obvious reasons if they didn't want that feature to be in place, so that means they may have left off a wire purposely.
Otherwise this system likely has a bad relay that would need to be replaced by Sidewinder. For that you need to send the main unit when you locate it to them for this as that part is only available trough them and needs specialized surface mount soldering to remove and install.
If that is the case, you will need to send them the main unit.
But also check this owners manual and it will contain all the information you should need. Even though its not the one you have most likely(wont know until you locate the model #)
But these are all very similar;-)
And If you will rate kindly at this time I will stick with you until we have this working as it should.
Pleas check ths manual out in detail:
Visit this site for that one. Once you have given me the correct model I can locate the exact manual for you. Also I can call you if you would like let me know but there is an additional cost of $10.00 for that.
Here is the site you need:http://www.manualslib.com/manual/226545/Dei-3500esp.html?page=1
Yours system is manufactured by DEI.
In any case, I will stick with you until this is complete.
Please rate kindly thus far, it won't cost you anything to rate my service to you kindly,
Then you can reach me by simply replying to this message anytime.
Thank you and have a wonderful evening!