What if your 1997 mustang key is broke off in trunk and you have a second it will crank but cut back has no chip i lost the one with chip?

That's a tricky situation. Since your second key (the one without the chip) can crank the engine but then cuts out, the problem is almost certainly the missing transponder chip in your original key. The car's immobilizer system is preventing the engine from running because it doesn't recognize the key.

Here's what you can do:

* Try getting a replacement key made with the chip: This is the most straightforward solution. You'll likely need your Vehicle Identification Number (VIN) and possibly proof of ownership. You can try a locksmith specializing in automotive keys, a dealership, or an auto parts store that offers key programming services. They should be able to cut a new key and program the transponder chip. The cost will vary depending on your location and the service provider.

* Consider having the immobilizer system bypassed (Not Recommended): This is technically possible, but it's generally not recommended. Bypassing the immobilizer system is a complex procedure that could potentially damage your car's electrical system or even void any warranties you might have. It also makes your car more vulnerable to theft.

* Check if you can access the trunk another way: Before resorting to more complex solutions, see if there's an alternate way to get to your broken key. Is there a rear seat release inside the car that could provide access to the trunk? If the car has a remote trunk release, try the remote.

In short: Focus on getting a replacement key made with the transponder chip. This is the safe and reliable way to solve your problem. Avoid bypassing the immobilizer system unless you're extremely knowledgeable about car electronics and are comfortable with the potential risks.