Hi  On my aircraft these are located under the crowl real close to the battery  [right side] they are there to keep the clock running when the master is off.

HI  Well here is where you can get them www.cessnaparts.com part no s1090-2 but sit down when you find the cost I would call a used parts aircraft dealer. go to www.google.com type in  used aircraft parts and find someone close to you. Ron

Hi Mr going fishing!! I never would do it! BUT, alot of owners would just go down to a auto supply and get one almost the same for the $5.00 it would never be checked if you crash or have a check ramp check. If you bought your Plane used you already have lots of auto items and you have someone else to pass the blame onto.    Gone Flying Ron

They say that confession is good for the soul, so here goes.  After checking the price at IWantCessnaParts.com, I went to Radio Shack and bought one for about $2 and installed it myself.  Part 43 lets you repair the landing light wiring yourself, so I thought this wasn't too much of a stretch (I'll say I mistook it for the landing light circuit).  If you read about me piling up my 172, tell the NTSB to check the clock fuse holder for the probable cause.