I am currently re-wiring my '55 for 12 volts. I am using the stock gauges and have installed a resistor to give the gauges the proper 6 volts. My question is for the temp gauge. I have a 1989 302 installed and want to know if I can use the 1989 temp sender or do I need the 1955 version?
You need the voltage convertor which will supply 6 volts to the gauge. Using the sender unit you have may or may not have the gauge working correctly. If you want to be sure of correctness use the 6 volt sender. It all gets down to the resistance of the sender at varying temperature.
Ford continued the use of 6 volt gauges into the early 80's,this is what works about best for your situation: http://www.ebay.com/itm/281469368054?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT And yes, the sender should match the gauge so use the 6 volt early sender. Read this! http://www.ebay.com/gds/6-to-12-Volt-Conversion-1955-Ford-/10000000001571127/g.html
12v will fry 6v gauges in pretty short order. Until the mid 80s or so Ford's gauges were 6v except for the '56 model year when the whole electrical system went to 12v, including the gauges. For some reason, maybe somebody here knows, they went back to 6v gauges in '57 and used cluster voltage regulators to drop the gauge volts to 6. Most modern senders are not compatible with the King-Seeley gauges Ford used. K-S gauges operate on the heated bi-metal principle where the sender and the gauge contain matching bi-metal strips. As, say, the temperature sender heats up or cools off the bi-metal strip in the sender bends or straightens slightly and modifies the voltage p***ing through it to the gauge. The strip in the gauge more or less bends the same amount and moves the pointer to a sort of appropriate spot on the face. Modern gauges work directly off resistance instead of a fiddly bi-metal mechanism.
That's what we are telling you. The only Ford of the era to use 12 volt gauges was the 56. You need to use a voltage reducer as mentioned earlier.
I have decided to go new school. I'm going to install this in the hole that would normally house the heating controls. Solves my temp issue and gives me more.