89 eldorados security system wont alow car to start?

89 eldorados security system wont alow car to start?
Try disconnecting the battery, and pulling the (Big) plug out of the main control unit, effectively cutting all power to the alarm system and any applicable relays attached to it.
HINT: the main unit is usually hidden up under the gas and brake pedals somewhere, have a good look, they like to keep it close to the ignition and inside the vehicle

check to see that the siren does not have a back-up battery, in the case it does, disconnect that also from the main unit.

(siren may sound wen disconnected, use the key to turn it off at the back of the siren, or shove a pillow over it till the battery goes flat.)

leave it disconnected for 5mins, (just to be safe)
reconnect the battery,
Try starting your car now, if it dont start, reconnect everything.
This is resetting the alarm controller unit.

if this dont work:

you better clear the weekend, and buy a multimeter..... and uninstall the alarm. or find the faulty relay that is attached to the ignition circuit. (theres always one immobilizer on the coil, coilpack, or what ever is used to distribute the "spark"
then there could be one attached the the "brake light" circuit, one on the tach, one on the ACC wire, one on the fuel pump (should have a relay), there are many possibilities,
the key is disconnecting the relays!!! sometimes u get a clever guy install "NO" (normally open) relays....

This should help ya