Wierd electrical/antitheft issue

[cluelesstang01]

I have a 99 V6 35th Anniversary Edition convertible Mustang the only way to start the car is to jump the starter relay circuit with the ignition on. After doing this the car runs as smooth as a baby's butt, but the odometer light flashes bright to off kind of like the four way flashers are on. it'll stop for a period of time and then go back to doing it even when car isnt running and no key in ignition. will not start with the key the theft light does blink (there was one time in which I fired it up jumping the starter relay circuit allow the car to run for about 15 minutes and then I shut it off and it started about three different times.)
then it started blinking, the part lights blink, no car alarm sounds, as far as the horn. someone wired in some LED lights but it looks like they were only Plug and Play. I know this is a long post for it to be my first one but I bought this car for my 17 year old nephew knowing that it needed a transmission but I have no idea what this electrical issue is I pull on the headlights and the headlights do not come on I checked all the fuses or at least I think I did and everything under the hood and under the dash seem fine please help.

Pics and videos as soon as I know how......

 

[cluelesstang01]

I'll get vids up as soon as I can

 

[ttocs]

I have a 99 V6 35th Anniversary Edition convertible Mustang the only way to start the car is to jump the starter relay circuit with the ignition on.

You need to check pin 85 or 86 on the starter relay to see if it is getting the 12v trigger from the key. One pin should show ground, the other should ONLY show 12v while cranking

After doing this the car runs as smooth as a baby's butt, but the odometer light flashes bright to off kind of like the four way flashers are on. it'll stop for a period of time and then go back to doing it even when car isnt running and no key in ignition. will not start with the key the theft light does blink (there was one time in which I fired it up jumping the starter relay circuit allow the car to run for about 15 minutes and then I shut it off and it started about three different times.)

not sure here

then it started blinking, the part lights blink, no car alarm sounds, as far as the horn. someone wired in some LED lights but it looks like they were only Plug and Play. I know this is a long post for it to be my first one but I bought this car for my 17 year old nephew knowing that it needed a transmission but I have no idea what this electrical issue is I pull on the headlights and the headlights do not come on I checked all the fuses or at least I think I did and everything under the hood and under the dash seem fine please help.

Pics and videos as soon as I know how......

 

[cluelesstang01]

 

[ttocs]

that is an aftermarket alarm. If there is a starter kill it could be disconnecting the starter wire. Follow the wires from the switch/led to the main alarm module and see what brand/type it is.

 

[cluelesstang01]

 

[badass98svt]

Is the theft light on the dash blinking in a certain code (2 blinks -pause- 7 blinks for example)

You definitely have an aftermarket alarm. Follow the wires and remove all that junk.

 

[ttocs]

the lights flashing is the alarm triggering and someone either cut the horn or siren wire probably thinking that would get rid of the alarm.

Again test terminals 85/86 on the starter relay while the key is in crank. One should show ground, the other should go to 12v while cranking. If you are missing the trigger there then I would look at the ignition switch which is an easy fix or there could be a starter kill on the alarm stopping it, again an easy fix

 

[cluelesstang01]

Thx fellas, I'll report back by this weekend. No particular sequence

 

[ttocs]

also have you tried a different relay?