I always check ground on the sender and gauges first.
If you use a regular ceramic resistor, your fuel gauge will work, but will be really jumpy as the runtz resistor corrects for this, but I'm not sure how. I have runtz resistors on my 52 and 53 and a regular resistor was on the 39 when I bought it. The gauge in the 39 is jumpy, but settles out at steady state.
Chris
