The sending unit in the aux tank on my truck is bad and I can't seem to locate a replacement. Anyone know where I can get just a universal one (electrical) to replace the one I have?

Try transerflow.com

Try www.auxtank.com or J.C. Whitney

are you sure you have a sending unit in the aux tank I thought there was only a pump to send it to primary tank as needed. if this is the case there is a tsb to fix it if you are interested let me know.