I assume you are referring to the Battle of Castle Itter, in which a combined force of French POWs, Austrian resistance fighters, US soldiers, and Wehrmacht soldiers defended the castle against an attack from the SS.

Castle Itter had been taken over by the SS under the orders of Himmler in 1943 and turned into a prison camp for high profile French prisoners: politicians, generals, celebrities etc. At the start of May in 1945, the prisoners smuggled out a letter asking for US help, carried by a prisoner who worked in maintenance. This person found the 131st 103rd (thanks /u/Rittermeister) Infantry Division, but was told that they could not launch a rescue operation as Castle Itter was not near their objectives. They did promise to raise the issue with their headquarters. An attack was authorised but it failed due to heavy shelling from German positions.

On 2 May 1945, the camp commander was found dead and many of the SS guards departed. The prisoners took over the prison and seized the armoury. They then put themselves under the leadership of Kurt-Siegfried Schrader, an SS officer that they had befriended during their time in prison and had gradually become disillusioned with the Nazi regime. They also sent a second person to get help from US troops. They found the Austrian resistance fighters, who in turn contacted Major Joseph Gangl. The Wehrmacht was in full retreat, but Joseph Gangl and a not insignificant number of soldiers took the opportunity to defect under his leadership. Gangl had collaborated with Austrian resistance groups for some time, and when he finally defected he was made the leader of the local resistance group. This was extremely dangerous for them, as the SS were acting as a rearguard and shooting anyone thought to be a deserter or Austrian resistance member. Gangl and his men were now both.

When the resistance learned that US troops had taken the town of Kufstein a few miles north of Castle Itter, Gangl surrendered to Captain John Lee of the US 12th armoured division. When he did so, he told the US soldiers about Castle Itter and the VIPs detained there. Lee immediately offered to lead a rescue mission and, since he was actually nearby (the 103rd Infantry Division was some 40 miles away, Lee's unit was 8 miles away), they were permitted to do so by their HQ. The SS rearguard had damaged the bridges in the area, and Lee determined that the bridge to Castle Itter could not take the weight of a tank. Since his was an armoured division, this wasn't good. There were also suggestions that an SS division was aiming to retake the castle and was closing in on them fast. A decision was made to send the one truck that the bridge could take, loaded with 11 German soldiers (including Gangl), 14 US soldiers, and the driver. The goal was to stall the SS division long enough that a proper relief force could arrive.

The VIP prisoners were supposed to hide somewhere safe whilst the fighting took place, but many refused, such as the tennis star Jean Borotra and former prime minister Paul Reynaud, and fought from the castle walls. On the morning of May 5th 1945, the SS division arrived. Gangl tried to get some reinforcements from the Austrian resistance group in the nearby town of Worgl, but they were fighting the SS as well and could only spare two Wehrmacht collaborators and an Austrian teenager. Jean Borotra also jumped down the wall and ran past SS soldiers to reach the 142nd Infantry Regiment, which was engaged in nearby fighting, to get reinforcements from the US.

The 142nd diverted their path to reach the castle. They arrived around 4pm and quickly defeated the SS division which was trying to storm the castle, taking around 100 prisoners. Their timing was impeccable, as the defenders were almost out of ammunition. Gangl had been killed trying to protect Paul Reynaud from an SS sniper. He was the only one of the defenders to be killed. 4 other Wehrmacht were injured, but nobody else.

So yes, what you have heard is true. On May 5th 1945, a total of 14 Wehrmacht soldiers (and the SS defector Kurt-Siegfried Schrader) helped defend Castle Itter from an SS division.

Source: Harding, Stephen. The Last Battle: When US and German Soldiers Joined Forces in the Waning Hours of World War II in Europe. Hachette UK, 2013.