I have a 4.0 L Straight 6 99' GC Laredo, if I look on the drivers side of the engine block I can see boots going into the cylinder block with wires attached to them. I have been mistaking these for sparkplugs which I just learned are on the other side underneath the coil rail. What are these boots and wires for? Are they sensors?

Thanks!

i think those are block heaters, used to heat the engine when the weather is freezing cold