'93 F-150, third brake light?

Dan't know how much you know about electrical stuff. We'll probably need some guidance on that side. What I did on mine is use a tap to the brake/turn circuit on each side in the rear. It is easy to run the wire down the stake hole to the lamp or the harness on each side. You can get to it easily by removing the tail light assembly. Went to radio Shack and got a couple of diodes. Sorry, I don't remember the exact value. I think the idea is to get something higher than what is actually needed. The feed from each brake lamp circuit gets one turned the correct way to feed power to the lamp. They will join together at the lamp to feed the third lamp. Ground the lamp as you normally would. What happens is you have power to the third brake lamp from either brake lamp. The diode prevents a crossfeed to the other side so that the brake lamps do not know what the other is doing when the turn signal is working. I don't recall the specs on the diodes. I think the big thing is handling the wattage rating of the lamp. You will need to check that to get the right diode. Seems to me that the ones I got were rated for 50 watts or so each which is well above what I needed. You can find the brake light feed at the lamp pigtail by just turning on the turn signal while you probe them with a test light to find power.

Lugnut

I'm pretty handy, but I'm having a hard time envisioning what the diodes would accomplish here - wouldn't that allow the light to flash when either turn signal was activated but you *weren't* braking? I've also found some "logic modules" intended for this application but I'm having a hard time envisioning how one could be 100% foolproof; I've been drawing a couple logic diagrams in my head and the best one I could come up with still could be fooled if you had the turn signal on and stepped on the brake during an "OFF" period for the active turn signal and therefore the third brake light activation would be delayed by a second or so. Since the whole purpose of the light is to give fast and unambiguous indication of brake activation it seems like I should just run the wire and be done with it.

Some sites I've found have indicated that a '93 *should* have a third brake light in the back of the cab from the factory, but mine does not

- it's only a cargo light. Do you think the wiring would still be there from the factory? I can't check as the moment as the cap is on the truck (how else was I going to get it home?) and I don't have a handy helper to remove it again (but I will have to as it is just sitting on the rails with no tape; I bought it yesterday so didn't have the opportunity to stop at my FLAPS and pick up some tape on the way.)

thanks,

nate

I can't find the diagram that was originally used. I did a quick Google and found this which may be the ticket for you

Tiny URL:

Just cut into the exsisting brake light wire at the rear of the truck put a weatherproof connection on and wire in the 3rd brake light. A word of warning, if the Cap brakelight is on the door of the cap be prerared to repace the wiring every once in a while. Reason as you open the cap door you are bending the wires and they will break.

That's the thing, *is* there a brake light wire? Where should I be looking for it?

thanks,

nate

If the truck doesn't have a CHMSL, the cap isn't required to have one so you could simply ignore it. On my truck the CHMSL is fed directly off the brake switch. The regular stop/turn lamps are fed from a stop lamp relay that feeds the turn switch. If you have a relay I'd try to tap the output from there.

That's the thing, *is* there a brake light wire? Where should I be looking for it?

No there is not "just" a brake light feed wire at the rear. And unless the feed is aquired before it goes through the turn signal switch, its going to blink when you use the trun signals for the side you pulled it from because the brake light and turn signal use the same feed wire on each side. The turn signal switch breaks the conection to what ever side is activated to blink, otherwise both would blink. I happen to think third "eyes" are a good idea, anything that might catch the attention of some idiot doing everything under the sun behind the wheel but drive and keeps him/her from rear ending me is a good idea. I always like to put some lights in the cap so I can see what I might be searching for at night, so running an extra wire from the brake light switch wouldnt be a big deal for me. I use a 4 wire trailer connector to run barke light power and ground as well as power feed from a switch in the cab to the cap. and since I am an old trucker as well, I usually like few clearance lights on the cap, which the four wire conector allows me to do. This also gives a quick disconnect when I need to remove the cap.

Whitelightning

I found the wiring diagram. The third stop light is fed straight from the stop light switch. LT GRN color. You could buy a kit that has the logic curcuit as well as the lamp housing, been there, done that.

wws

You have a wiring diagram? which manual is it in? I looked all through the body service manual last night and couldn't find it. (yes, I did buy some used manuals off fleaBay)

nate

This article says for 97 and newer but there might be something similar in your wiring harness. Probably not but it doesn't cost anything to read the article.

Cheers, Lawrence

ME?, no. Online reference:

user id: lib password: access

Pretty neat, huh?

wws

nate

Sweet. yeah, that's more like what I need, just something simple that tells me about where to look and what color wire to use. thanks a bunch!

nate

(bookmark> ME?, no.

Follow up - got it done yesterday, I just ran the wire because a) I was adding mechanical oil pressure and vacuum gauges anyway so I had to drill a hole in the firewall anyhow and b) I just didn't see how a logic module would work perfectly all the time. So it's done. I found a connector under the center of the dash with a brake light signal on it, just tapped off of that with a scotch-lock. Also found that there is a pressure tap for the trans with 1/4" NPT thread right above the pan on the driver's side, that's where I put the temp. sender for the trans temp. gauge. all back together now, hands are a little busted up but truck is ready for inspection as soon as my new cap door latches show up (might be here today or tomorrow) Probably the most frustrating part of the job besides running the wire in the split loom all the way back (hint: I used about a 18" piece of solid THHN with an uninsulated crimp connector on the end of my new wire to push it through tees, etc.) was finding gauge power - there's not a whole lot of slack in the wires behind the gauge panel, but I got it done.

For the first time in about six months I have the facia back on the dash so the truck doesn't look so "ghetto" (I never did get the oil pressure gauge in the dash working properly; I had a mechanical gauge zip tied to one of the vent openings, I finally mounted a proper three gauge panel as part of this whole exercise) but my vents are still all busted, I haven't bothered to look for replacements, new ones from LMC are expensive!

thanks to all

nate

On Feb 29, 7:05=A0pm, Nate Nagel wrote: