I thought this might be of interest to someone else. I live where I often have thick fog in the morning and have often left my headlights on and run the battery down.
I have been looking for a clean way to wire a relay that would disable the headlights when the key is off and finally found a very clean installation to accomplish this goal.
My first thought was to get at the wires feeding the headlight relay, but then I realized it is at Relay Block No. 2 in the engine compartment on top of the left fender, and the taillights are fed from a relay in Relay Block No. 1 on the left front quarter panel. This didn't make it very convenient to control both.
It finally ocurred to me that I could just disable the ground to the relay coils for both of these relays. So I traced this through the lighting multi-switch on the steering column. It turns out there is one wire readily accessible at connector C15 on the bottom of the steering column which feeds the ground through the light switch to both the headlight relay and the taillight relay. And the dash indicator illumination also feeds from taillight relay. So by interrupting that ground with an extra relay, which in turn is powered from the Gauge fused circuit that gets power via the ignition switch, all of these lights will be disabled any time the ignition is off. The new relay coil current is not a problem to add to the Gauge circuit. It is used to feed several other relay coils and seems like an appropriate place to power it.
Here is a schematic of the main circuit details to explain how it is connected:
Note that there are two wires at C15 that are white with a black stripe, a thin wire (about 20ga) at pin 11, and a fatter wire (maybe 16 ga) at pin 9. You want the thinner wire at pin 11 which just feeds a ground to the relay control coils. The fatter ground wire provides ground to some of the lights.
My apologies for the photo quality. Hard to get shots under the dash. My flash washes everything out, so I ended up using a maglight for lighting and photoshop to clean them up a bit.
Here is a pic showing where I mounted the extra relay on the support brace that runs from the left side of the center hump up to the dash (right next to your calf when driving, but up higher). There are several unused holes in this strut with threaded nuts welded to the back side, making an ideal mounting spot:
Here is a shot of the wire attached to pin 11 of connector C15. You need to cut the thin white/black wire at pin 11, about an inch from the connector. Then you splice the red wire to the connector side of cut wire, and the green wire to the other side of the cut wire. This shot shows the splices before I put heat shrink over them.
This shot shows all three places where wires run. The yellow wire runs from the back side of the fuse block at the left side in this view, to the splices at C15, then these three wires run to the relay in the right side of this photo. This makes the entire installation pretty straightforward. Everything is within eighteen inches or so.
So here's another version of that last photo but with some highlighted lines added to make it easier to see where the wires are routed. If you look closely in the previous photo you may be able to see some of this. I ran the wires in braided black nylon sleeving for abrasion protection. The only real critical wire is the yellow one, since it carries keyed fused 12V. The red and green wires are just grounds.
Of course you don't need to follow the color code that I used for the added relay circuit, that's just what was on the relay socket I had handy, and they show up well in the photos. Just be sure you connect to the correct wires in the existing circuit. There are really only two spots you have to identify correctly. the fused side of the 10A gauge fuse (should be a yellow wire), and the thin white/black wire at pin 11 on C15. It really could not be much easier. To be sure you get the correct side of the fuse, pull the fuse, turn on the key, and the side you want should be dead when the fuse is pulled, the other side will be 12V. The wiring diagram indicates this wire should be yellow, but mine was yellow with some silver dashes on it.
Works great! It is now impossible to leave my headlights on.
If you really wanted to be clever, you could modify this to allow the relay coil to remain energized for several minutes after turning off the key, like some newer vehicles do. Or if you really want to be able to run the headlights without turning on the key, I suppose you could parallel the relay with a toggle switch, but I haven't been able to figure out any reason to need that.
I hope someone else finds this useful. I have been wanting to do this for a couple years and just finally got the time to get it done. I know that I killed at least one battery because I didn't have this.
Cheers
-ts
I have been looking for a clean way to wire a relay that would disable the headlights when the key is off and finally found a very clean installation to accomplish this goal.
My first thought was to get at the wires feeding the headlight relay, but then I realized it is at Relay Block No. 2 in the engine compartment on top of the left fender, and the taillights are fed from a relay in Relay Block No. 1 on the left front quarter panel. This didn't make it very convenient to control both.
It finally ocurred to me that I could just disable the ground to the relay coils for both of these relays. So I traced this through the lighting multi-switch on the steering column. It turns out there is one wire readily accessible at connector C15 on the bottom of the steering column which feeds the ground through the light switch to both the headlight relay and the taillight relay. And the dash indicator illumination also feeds from taillight relay. So by interrupting that ground with an extra relay, which in turn is powered from the Gauge fused circuit that gets power via the ignition switch, all of these lights will be disabled any time the ignition is off. The new relay coil current is not a problem to add to the Gauge circuit. It is used to feed several other relay coils and seems like an appropriate place to power it.
Here is a schematic of the main circuit details to explain how it is connected:
Note that there are two wires at C15 that are white with a black stripe, a thin wire (about 20ga) at pin 11, and a fatter wire (maybe 16 ga) at pin 9. You want the thinner wire at pin 11 which just feeds a ground to the relay control coils. The fatter ground wire provides ground to some of the lights.
My apologies for the photo quality. Hard to get shots under the dash. My flash washes everything out, so I ended up using a maglight for lighting and photoshop to clean them up a bit.
Here is a pic showing where I mounted the extra relay on the support brace that runs from the left side of the center hump up to the dash (right next to your calf when driving, but up higher). There are several unused holes in this strut with threaded nuts welded to the back side, making an ideal mounting spot:
Here is a shot of the wire attached to pin 11 of connector C15. You need to cut the thin white/black wire at pin 11, about an inch from the connector. Then you splice the red wire to the connector side of cut wire, and the green wire to the other side of the cut wire. This shot shows the splices before I put heat shrink over them.
This shot shows all three places where wires run. The yellow wire runs from the back side of the fuse block at the left side in this view, to the splices at C15, then these three wires run to the relay in the right side of this photo. This makes the entire installation pretty straightforward. Everything is within eighteen inches or so.
So here's another version of that last photo but with some highlighted lines added to make it easier to see where the wires are routed. If you look closely in the previous photo you may be able to see some of this. I ran the wires in braided black nylon sleeving for abrasion protection. The only real critical wire is the yellow one, since it carries keyed fused 12V. The red and green wires are just grounds.
Of course you don't need to follow the color code that I used for the added relay circuit, that's just what was on the relay socket I had handy, and they show up well in the photos. Just be sure you connect to the correct wires in the existing circuit. There are really only two spots you have to identify correctly. the fused side of the 10A gauge fuse (should be a yellow wire), and the thin white/black wire at pin 11 on C15. It really could not be much easier. To be sure you get the correct side of the fuse, pull the fuse, turn on the key, and the side you want should be dead when the fuse is pulled, the other side will be 12V. The wiring diagram indicates this wire should be yellow, but mine was yellow with some silver dashes on it.
Works great! It is now impossible to leave my headlights on.
If you really wanted to be clever, you could modify this to allow the relay coil to remain energized for several minutes after turning off the key, like some newer vehicles do. Or if you really want to be able to run the headlights without turning on the key, I suppose you could parallel the relay with a toggle switch, but I haven't been able to figure out any reason to need that.
I hope someone else finds this useful. I have been wanting to do this for a couple years and just finally got the time to get it done. I know that I killed at least one battery because I didn't have this.
Cheers
-ts
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