Whats usually causes the trim position gauge to read incorrectly? Mine worked for most of the summer then started to ready incorrectly and now is way off. Showing trailering position with the drive all the way down...
Ok, I had to think about this one a bit and did some checking. You have your signature backwards. You have an 290A transom shield, intermediate and upper gear housings, with a 270 lower unit. Found your pictures http://forums.iboats.com/showthread.php?t=529057&p=3604910&viewfull=1#post3604910
The brochures all show the AQ231A having only the SX-A drive, but yours looks like a 290 shield and a 290 upper. The 290A and SX-A are virtually identical.
So, in that case, you do have the potentiometer and you should really test it before buying. They are spendy.
here are the testing procedures. It's not found in any of the service manuals.