until 56 all original temperature gauges were mechanical, which is what those that operate via a Bourdon [capillary] tube, filled with ether, are called, an electric gauge in a 55.2 would be a replacement, or possibly end of the year production, although the earliest 56's also had mechanical gauges

maybe your electric sender isn't sensing properly because it doesn't fit the location as the original mechanical bulb did, I believe the location and hole size for the sender changed for the electric gauge, you may have an adapter there affecting it - here's a mechanical gauge for sale

Bill

Last edited by red58; 07/02/2013 1:04 PM. Reason: after thought
Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics