Here we have some nice color diagrams of the MGA bonnet latch from our friendEric Welty . Perhaps this may help to show how the MGA bonnet latch works, and why it sometimes doesn't, and how to fix i The top green line is the bonnet support bracket welded into thbody. The bottom green line is the shorter fixed bracket bolted underneath. The yellow parts are tube spacers (around the bolts) that maintain an open space between the brackets. The red line is the sliding latch plate with pull rod on the right and return spring on the left. The gray part in the center is the vertical latch pin that is attached to the bonnet. The moving pin has the enlarged tapered head with flat shoulder. Notice that the bottom green plate has a short vertical finger extending downward at the left side of the open hole.

As the bonnet is being closed, the latch pin is pushed down into the center hole as the slider is pushed to the right. When the latch pin head goes below the sliding plate, the slider will be pulled back to the left by the spring, catching the latch pin head under the slider, as shown below. Notice the hanging finger on the bottom plate should prevent the latch pin head from moving to the left of center when the bonnet is latched. Pulling the slider to the right should un-latch the center pin, to release the bonnet.

Notice that the spring loaded slider tends to push the latch pin to the left. If the latch pin is adjusted too long, or the bonnet is pushed too far down when closing, then the latch pin head might be pushed excessively down to end up below the short hanging finger of the bottom plate. That is how the latch pin might end up stuck underneath the hanging finger with the bonnet firmly stuck shut.

Another fairly common fault or mistake is having the bottom fixed plate installed backward with the hanging finger on the right side of the center hole. That can allow the latch pin to move left and be trapped under the flat part of the bottom plate with only a small amount of overtravel. As such, it is important to have the bottom plate assembled with the hanging finger on the left, toward the return spring, away from the pull rod.

Unsticking the bonet latch can be a royal pain as you cannot get your hands behind the grille. Some people have welded a small washer onto a steel rod to reach through the grille slats to manipulate the tip of the latch pin. Tie back the bonnet release pull rod to hold it back while a helper might push down the front of the bonnet to relieve the spring load on the latch pin while you try to nudge the pin back to center.

If all else fails, you might use a 1-1/4-inch hole saw to cut a hole in the air pan under the latch pin. That would be on center, 5-1/2-inches forward from the rear edge of the air pan.Then you can use a 2-foot length of steel pipe to reach up from the bottom to push on the latch pin. Once you get the bonnet open, you can put a snap plug in the new hole, maybe paint it body color. If you ever have to do this again, just punch out the snap plug for access.