Alternative Fuel: Install a 12 Volt Stainless Steel Resistance Wire Injector Line Heater

This article will show you how to install an injector line heater on a 5 cylinder 1985 Mercedes Benz 300D. The basics installation will be the same for most engines. This heater is broken into 3 sections by 6 inch spacer wires. The spacers allow the heater element to bridge the larger gaps between the injector lines. A one piece heater will work, but you lose a few inches of contact area as the element jumps from line to line. I like to hold one wire on each of the battery posts to ensure that the heater is not damaged before I install it. It will get hot fast, so be careful.

The injector lines have clamps to reduce vibration. Remove the clamps near the injectors. The clamps near the injector pump (IP) can stay. You need to clear about 7-8 inches on each line. Lay out the heater on the inj. lines. Make sure everything will line up before you start to tape them down. Fold the 14 inch element in half. Position it on the inj. lines so you can jump to the next line where the lines are close together. Use the spacer to get to the center inj. line. The spacer gives you some play to position the heater closer or further from the IP if needed. The other spacer will get you to the last 2 inj. lines. Again fold the element in half and position it on the lines. You can start to secure the heater when you are finished the lay out.

Set up some 6-8 inch pieces of the high temp tape where you can easily reach them. The short pieces are easier to work with and should be long enough to wrap one inj. line. The tape will stick to itself and will usually not come apart, so be careful with it. Start at one end and work your way to the other. Don't jump around or it may not line up for you. Keep the overlap to a minimum as you wrap the lines. It does not take much to secure the heater. I use a couple extra wraps around the end and beginning of the heater to give it some support in case the power or ground wire is pulled accidentally. Do not use any other tape. Only high temperature tape will hold up to the heat. Make sure that no rubber, plastic or other wires or hoses can touch the heater. Use some clamps or wire ties (zip ties) to secure anything near the heater.

I like to test the heater at this point before I finish the installation. I choose to use the wire near the front of the motor as the ground because I want to power the other wire. Find a convenient bolt to use to ground the heater. Anything that will conduct electricity will work. Measure and cut the ground wire. Crimp a ring terminal to the wire and secure it under the bolt. If it's dirty or rusted like this motor, clean the connection with a file or wire brush. Touch the power wire to the positive side of the battery. Use a jumper wire if it will not reach. You should see a small spark as you brush the wire on the battery post. Powering up the heater will check your ground so you can rule it out if there is a problem later.

Think about how you want to power the heater and your other 12 volt components like switching valves. One inj. line heater will draw about 7-8 amps. Some people wire the heater so it is on when ever the engine is on. Others like to use a switch. The simplest way is to use a test light to find an ignition hot in your fuse box. An ignition hot will light the test light when the key is in the run position and will turn off when the key is turned off. Try to use a circuit that has a 20 amp or higher fuse so it can take the extra load. The auto parts store will have a kit that makes it easy to tap into the fuse box. A ring terminal can be slipped between the fuse and the fuse holder on a Mercedes so no kit is needed. If you want or need to use a relay you can use this circuit to power a switch to control the relay. I like to supply the relay right from the battery and find an ignition hot under the dash to power my switch. Doing this way minimizes the amount of wire you need to install. If you are using a relay you can tap into any ignition hot because the relay will draw very little power. An ignition hot will turn off the relay when the key is removed, giving you a built in safety if you forget to turn off the switch when you leave the car. Make sure you have a fuse protecting all of your wiring. If something shorts out without a fuse it can start a fire.