Hey ladies and gents, Happy Thanksgiving. I installed the Bosch relay (part #0332019150) Headlight Control modification in my 1996 Ram 2500 yesterday and learned a lot that I want to share with those that are considering doing this mod - and you should be. I looked everywhere for an exact method to do this modification but gave up, drew myself a simple ladder-logic schematic and went at it.

This post is simplified for the non-electricians out there looking to perform this mod themselves. A ladder-logic schematic, in my opinion, is the simplest one to make the idea hit home. One simply follows the "ladder" rungs from top to bottom to follow the flow of electricity and location of wires.

OK, let me explain a few things: electrical devices (headlight switches for instance) are designed (sized) to carry "X" amount of current, measured in AMPERES (amps). Headlights draw a lot of amps, and Chrysler totally cheaped out on their headlight switch (and wire sizing) to improve their bottom line. They did not design their trucks to last forever. On the contrary. So they saved a few dollars on each unit by undersizing all of their electrical equipment (yes, they did). Yay for their stockholders. The rest of us are left holding the bag - as it were.
Let's keep this easy: The bigger the wire (sized in AWG) the more amps it will continually carry to do the work. Big wire carries lots of amps safely, small wire will carry fewer amps. What happens if you try to push more amps than it's rated for through small wire? It gets hot from resistance (measured in ohms) and eventually can turn red hot, burn off the insulation and cause a fire. So you want to size the wire for the LOAD (the job you want to do). Chrysler engineered their vehicles to work with the absolute least amount of copper they could get away with and have it still work. That's okay until 25-30 years of continuous use goes by, then we pay for the money that they saved when your headlights go out on the interstate at 03:30 on your way to Track Day or grandma's for Sunday dinner.

Let's FIX it.

Google "How does a relay work?" and you'll get a lot better picture of why we want to do this mod. The coil in the relays draws a tiny amount of amps to energize. Like a 10th of an amp. But the CONTACTS inside these particular relays are designed to carry 30 amps continuously. So the idea here is to take the factory wires that run from the headlight switch to the headlights (big load) and connect them to energize only the tiny coil (small load) inside a pair of relays - one serving the hi beams and one serving the lo beams. Boom. The large load is instantly removed from the headlight switch and placed upon the (reliable and easily replaceable) relays.

In YOUR truck: When you're ready, to give it a go, REMOVE the driver's side battery and battery box. If you have two batteries, DISCONNECT the one on the right side as well, but it's not necessary to remove it. There's 2 bolts and 4 nuts holding the battery box in. 2 of them go through the fenderwell and are accessed under the truck. Once that's out, you'll see a fat bundle of wires that runs behind the battery box and behind the fuse box. You'll need to carefully remove the ribbed outer conduit and factory tape wrap on that bundle to find the factory headlight wires that need to be utilized. You will need to cut into and splice the low and high beam wiring to accomplish two things: 1) Establish 2 trigger wires that come FROM the headlight switch, to energize the high and low beam coils and 2) establish headlight power wires that will run from the relays TO the headlights. IN MY '96 TRUCK the LOW BEAM wires are purple with a white trace stripe. HIGH BEAM wires are red with an orange trace stripe. I found the fusible link for the low beams (where the wire from the headlight switch splits into the left and right wires of the same colors) right there. That's where I cut them. I removed the fusible link and spliced the trigger wire to the end coming from the cab. I then spliced the two factory wires that lead to the headlights onto one 12 AWG stranded THHN/MTW blue wire. DON'T ever use "Scotchloks" or cheap butt splice connectors. I use non-insulated crimp connectors and shrink tubing. If you don't have a good pair of Ideal terminal crimpers, invest the $35 and get them. They'll help you do the job right. The high beam fusible link and split must be further up the harness so I had the two red with orange strip wires to work with. I simply spliced the pair coming from the cab to another 16 AWG trigger wire. The pair headed to the headlights were spliced onto another single 12 AWG power wire to be connected to the high beam relay. Now, you've got 4 wires coming out of the harness: a low beam trigger, a high beam trigger, a low beam power and a high beam power wire. All 4 of these will connect to the relays as shown in the wiring diagram. Re-wrap and properly protect the thick harness and secure it to the fender well again. I mounted the relays on the battery box tab to the rear with the hole in it. You can find a better spot, but this was fast and offers easy access. I simply used a 10-32 screw, washers and a nylock to mount them.
Because the headlight connector wiring is a small gauge (AWG16?) and connectors of this type with heavier wires don't seem to be available, one may as well use the factory harness for the headlight wiring downstream from the relays. If someone knows of a heavy gauge wired headlight connector for the Halogen type bulbs in these trucks, please LMK.

You can see that I'd already added a terminal strip under the hood to get all those fusible links OFF of my battery terminal. I mounted a heavy duty Allen Bradley fuse holder (with a 30A fuse in it) on that DIN rail for the headlight power that runs through the relays. Not too crazy about these battery terminals, but I had to do something as the originals were cracking.

I soldered all of my connectors on. Not an easy job under the hood, but they'll never come apart. I like to say that "This job is easy - the SECOND time you do it." That applies here too. Not too hard but well worth the effort and the cost is VERY minimal for the return you get. Happy to answer questions. Sorry it doesn't sound as simple as it is.

 

I did the headlight upgrade on my 98.5 last year. I mounted two relays on each battery box. On the frame behind the factory wired headlight harness on each side of the frame is a plug containing three wires. Ground, low and high beam. I added wires from each high and low to my relays then wired them to the correct headlight. I bought all the connectors from Amazon and everything works as it should.