This is a line from the filter description of an item on Ebay.

You will need to hook the heater up to a on-off switch and relay (customer supplied) capable of handling a 16 amp (peak) load

Could I hook up to my present fuel heater wires or would this heater cause me problems?

need to know current draw of the heater vs OEM heater, but way to get around this is to have a 25 amp capable relay controlled by exisitng heater circuit, I don't know what the GM heater draws to say 100% OEM wires will handle 16a draw of your ebay heater.

You thinking of replacing factory heater or adding a supplimental heater for wvo/svo or other pre-heat use;

in that case you might consider using the temp switch of exisitng filter mgr as the "switch on" of relay's control coil, that way heater comes on at 60F automatically, and you could also incorporate a manual switch in parallel with the filter mgr signal and energize the heater on any time you choose.

I'm going to add an additional fuel filter/water seperator with heater.
I've never wired in a relay before and don't have a clue.
I run B-11 or higher

very easy a relay has terminals for control coil low current draw in mA range (less than 1A), and terminals for load side (what you are powering) current limited by rating of the relay, I'll see if I can find one in a and send pics.