yellow is for 10-12 awg wires, blue is for the next size down (14-16 awg), blue works good for these trucks. Yellow would require stripping the wire end at double-length and the folding it over before inserting into the connector - this is actually my preferred method of installing crimp connectors, as if done right the connector must fall apart for the wire to be able to pull out of it (I like overbuilding stuff, even my wiring), but the problem with the glowplugs harness is that some of the individual leads are a bit on the short side as is before you even cut the factory connectors off. My summer project will be a new glowplugs harness with 12-gauge wires of equal length with heavy-duty yellow connectors and double-fold crimp on them, plus the factory spring clips of course. Oh, and the Z-strip will be gone, for faster glow cycles...