Headlights - relay power conversion how-to (done on a '88 Town Car Executive, should work for other years too)



Parts You Will Need

First you need to go to Daniel Stern Lighting and read the article they have on relays. Then it's time to go shopping around for parts - I used four (overkill!) 30A Tyco relays with single 87 output terminals and just soldered two wires to each spade connector. Power wires to the relays are 12g, power wires from relays to headlights are 14g, all grounds are 14g as well. Take your time to find the correct spade connectors for the headlight tabs, don't reuse the old tabs as they are most likely corroded. If you can't find suitable spades you can always do like me and re-drill the small holes in the tabs and bolt the wires with 6-32 bolts and self-locking nuts (bend the tabs spreading them a little so the bolts don't touch each other).

Let's Get Started

After you have the parts you can go ahead and disconnect the headlights from their harness; save the plastic spade connector plugs if you can.

Power distribution to headlights goes like this:

grounds (all four lamps)

black wires

low beams (two outboard lamps)

red wires - high beams (all four lamps)

light green wires

Find a place for the relays where all these wires will reach, then cut the harness wires and crimp and solder to them new spade connectors that will fit over the relays tabs. You have the option of keeping the stock grounds and using them for the control circuit of the relays, or running new ones, it doesn't really matter - mine are cut off, I run all my grounds directly to the battery's negative post. Measure and cut suitable lengths of 12g wire for the relays slave circuits input, then crimp and solder spade connectors to the end that goes to the relays, the other end gets a ring terminal. The slave circuits output wires (14g in my case) get spade connectors in one end (to the relay), and a bigger spade connector or a ring terminal on the other (depends how you attach them to the headlights). Insulate all connectors with suitable sized heat-shrink tubing, I used two layers on top of each other. Run all the new wires where you want them, plug them in the headlights and connect them to the battery, then use some crinkly pipe and zip ties to keep them there.

Relay installation time! Assuming you are using the stock grounds (black wires), plug everything as follows:

• red wires - terminal 86 of two of the four relays (designated for the low beams)
• green wires initially going to the outboard (dual filament) lamps - terminal 86 of the other two relays (designated for high beams)

There is a catch here though - on the passenger side of the car the stock harness has one spade connector for the headlights with two green wires (not one like the other 3 connectors) soldered to it - make sure when you crimp and solder the new connector you have both of these wires in it again, and when plugging in the relays make sure this is the one that gets plugged in the relay for the passenger side low beams.

• green wires initially going to inboard (closer to grill) lamps - tape off ends well and let loose, there's another source for power in case you want to add driving lights to shine the road closer to the car while running on high beams
• black wires (all 4 of them) - terminal 85 on all relays, that's the ground. As said above you can actually cut all these wires off and run your own grounds, whichever you prefer
• input wires coming from the battery (all 4 of them) - terminal 30 on all relays
• output wires going to headlights (all of them, as many as you have) - terminal 87 (not 87a, that's different) on all relays

When running these make sure the high beams go in pairs and plug in the relays that have the light green stock wires connected to them too. The wires for the low beams go to the relays that have the red stock wires hooked up to them.

You're done!  Before you turn the lights on for a test make sure you have everything connected where it needs to be, especially at the headlights. Assuming you look at the lamps from the back (where the tabs are), the left tab is always ground, the right tab is always high beams input (wires coming from terminal 87 of the high beam relays), and central lower tab is low beams input (wires coming from terminal 87 of low beam relays). On the battery side run both high beam fat wires through a common 20A fuse, or two 10A individual ones, the two low beam fat wires get either a common 10A, or two 5A individual ones. Double check everything again, then go and light them up!

Performance suggestion - when running the output wires for the low beam relays instead of a single wire from each relay run a pair (that makes 4 wires total, just like the high beams), then swap the single filament (high beams only) inboard lamps of the car with dual filament lamps like the outboard ones (low and high combined) - that will allow you to have 4 low beams instead of the stock 2. And if you really want to be bright and shiny swap all 4 lamps with type 4666 ones, they are meant for cars that only have two headlights (not 4 like us) and as such are more powerful. In any case if running 4 low beams upgrade their fuse to a common 15A, or two individual 10A ones, as there will be more current flowing.