Quality jumper wires can be pricey...test leads

When you replace a block heater, save the electrical cord. It makes perfect jumper wires.

Split the cord into three. You’ll find that two will have the rubberized insulation and the third, which was the ground, will be a plain coated wire.

Solder on some protected alligator clips and you have a set of perfect length Jumper wires that are strong and flexible.