Image Credit: Hagerty/YouTubeIt isn't every day that you come across a classic American muscle car hiding away in someone's garage. But it can happen, as Hagerty found out when they went to check out a 1969 Shelby GT500 that had been in Mike's garage for a very long time.The car had been hiding away for over 30 years, and it is one of just 1,402 GT500s built during 1969. Finished in the stunning Gulfstream Aqua color, it is also one of just 43 that were finished in that color, adding to its value and rarity.Mike had acquired the car in the early 1980s, and at the time, it had narrowly avoided being towed as it had been abandoned. The Mustang had even survived a fire in the trunk before the last owner abandoned it due to constant electrical problems.AdvertisementAdvertisementIt then sat at Mike's home for 30 years, but when Hagerty presenters Dustin and Brito saw a photo of it in Mike's garage, they knew that they had to do something. So in a recent YouTube video, the duo went to check it out and to see if it would fire up again after over 30 years.What Condition Was the Shelby GT500 In?Initial inspections of the muscle car were promising, as other than the usual dust, the Shelby GT500 was in good condition. Thankfully, it had been securely stored inside for 30 years, so rain and water couldn't get at the car. After a quick wash, it already looked so much better, confirming the paintwork was in solid condition.Under the hood, it had a date-correct 428ci Cobra Jet V8 engine, and there was more good news. It wasn't seized; all the contaminated oil was easily drained out, and it looked to be in really good condition. That gave them confidence that they could start the engine, the first time in decades that this Mustang has had any life in it.Incredibly, it didn't take much for the engine to fire up. A few tweaks were needed electrically to sort it out. Plus, the car needed fuel, the radiator needed water, and there were a few other minor adjustments that needed to be made. But after this was done, and new spark plugs were fitted, the Mustang fired up for the first time in a very, very long time. It very nearly fired up at the first attempt, and on another attempt it spat fire out!This Is What Else Was Done to the Shelby GT500Image Credit: Hagerty/YouTubeThere was still plenty that needed to be done. There was a massive vacuum leak and a loose water pump pulley. Plus, there was a huge amount of smoke from the engine thanks to Marvel Mystery Oil used to try and preserve the engine while the car was stored. The more the car ran, the better things looked, with the power steering working as intended, and the oil pressure was very good.AdvertisementAdvertisementWith that sorted, the two presenters could get on with doing other work on the car. That included a lot of the wiring and electrical wizardry, something that Dustin would put a lot of effort into. Cosmetic work was also done to try and get the car looking as factory fresh as possible. A cooling issue also needed resolving, and this was done with some tweaks to the car's thermostat.The Mustang Ran for the First Time in DecadesImage Credit: Hagerty/YouTubeTowards the end of the video, the two presenters got the car back on the road again. Some things needed sorting, such as a cracked ignition coil and the elimination of a misfire. But when owner Mike saw it again, he was astounded, and he was able to take his first drive in the car since 1997. This was an amazing story, and Mike's face when his car was back in front of him showed that all the work was worth it.If you want more stories like this, follow Guessing Headlights on Yahoo so you don't miss what's coming next.