Hmm, every try the search function on the forum?
http://www.veryuseful.com/mustang/tech/airBag/airBag92.html
You have a code 51, that's not good in terms of easy debug.
You likely had codes before - something like a code for a bad sensor.
51 Diagnostic monitor internal thermal fuse open
Thankfully, the diagnostic monitors are cheap now. My guess is that you'll go through 1->3 of the monitors to hunt down the problem.
Note: You get two KEY TURN ONS before the internal fuse will blow. So, after the second, disconnect the battery, put your foot on brake pedal for 15 secs (to drain the caps in the EEC, radio, etc), wait 5 mins, connect battery, and you have get two KEY TURN ONS before the internal fuse will blow.
If you didn't get any codes before, it could be because of the "old electronics". Your best "bet" for best electronic life of a new diag monitor would be from a Northern Cold state, and from a car with low mileage (
hopefully correlating to engine run time). Commercial-grade capacitors are the "most likely" to fail from age, use, temperature (use Google if you want to know more).
http://www.veryuseful.com/mustang/tech/airBag/airBag92.html
51 Diagnostic monitor internal thermal fuse open
http://www.veryuseful.com/mustang/tech/airBag/airBag92.html#CODE51
Fault Code 51 - Diagnostic Monitor Internal Thermal Fuse - Open Due to Intermittent Short To Ground
Description: NOTE: The microprocessor inside the diagnostic monitor controls the internal thermal fuse. This fuse is not serviceable. The microprocessor will open the thermal fuse whenever a short is detected in the deployment circuits. The thermal fuse does NOT open because of excessive current flowing through it. DO NOT attempt to jumper out the thermal fuse with a circuit breaker or any other type of fuse.
NOTE: DO NOT install a new diagnostic monitor until the short has been located and corrected. If a short to ground has not been located and corrected, then the short to ground is intermittent and IS NOT PRESENT AT THIS TIME. If you install a new diagnostic monitor while there is an intermittent short in the system, the new diagnostic monitor will also open its thermal fuse and require repeated repairs.
Thankfully, the diagnostic monitors are cheap now. My guess is that you'll go through 1-3 of the monitors to hunt down the problem.
Note: You get two KEY TURN ONS before the internal fuse will blow. So, after the second, disconnect the battery, put your foot on brake pedal for 15 secs (to drain the caps in the EEC, radio, etc), wait 5 mins, connect battery, and you have get two KEY TURN ONS before the internal fuse will blow.
If you didn't get any codes before, it could be because of the "old electronics". Your best "bet" for best electronic life of a new diag monitor would be from a Northern Cold state, and from a car with low mileage (
hopefully correlating to engine run time). Commercial-grade capacitors are the "most likely" to fail from age, use, temperature (use Google if you want to know more).
The debug of a code 51 gets involved quickly. If a new diag monitor doesn't show the initial/main cause (remember, you get only 1-2 key turn-ons), and the procedure on the web page isn't clear (really requires some electronic and DVM experience), then a dealer may be the best bet. My "100%
pull it from my *ss guess" is ~~$500 (+/- $3,000
).
Good Luck!