tube-bed MJ, tail-light wiring...?

[BrettM]

I chopped my bed off and am having a hell of a time figuring out how to wire up some tail-lights. My Chiltons and (downloaded) FSM don't seem to have the wiring diagram I need either.


Short Version

I got these

wired up and when I hit the blinker with no brake it lights up that side but does not flash. when I hit blinker with the brake that sides light goes totally dark for 1/2 a second then back to normal.

To make things more complicated, that is with the key in the ON position, if I put it in ACC things get weirder.

what's the deal?

Long Version

The lights I got are these:

PM Stop, Turn & Tail Light Combination (V440l)

They are a 2 wire hookup; one for Stop and Turn and one for Tail. They ground through the mount.


The stock MJ configuration runs only 5 wires to the rear, two of which are ground and backup lights which we can ignore here. that leaves me with;
-blue (runs to both sides)
-gray/black (left only)
-brown (right only)

The blue I would assume be the Tail function. The gray/black and the brown I would assume to be the Stop/Turn function. In each tail-light there are 2 bulbs (exlcluding backup) each with 2 filaments. Both wires (blue and gray/black on the left, blue and brown on the right) go to both bulbs. So somehow these 2 wires are controlling 4 different filaments. I just don't get it.

I ran through every possible tail/brake/blinker/hazard combination possible checking each wire with a multi-meter and it just doesn't make sense.

What I have right now;

Blue wired to Tail wires, Brown and Gray/Black wired to Brake/Turn wires. The Tail and Brake functions work perfectly, as do the hazard lights. The blinkers are what is all wierd :wierd:

 

[MUDTRUK]

Hey Brett, why not get some led's? I got some 4" round ones from a tractor supply store by me and the hook up was stupid simple. Also led's are gonna be much brighter than the regular incandesents. Sorry, not much help. Good luck, hope ya had a good Christmas! Judd

 

[crazyoffroader]

Brett, your ground is bad, rewire the existing ground wires (harness) into the housing of the tail lamp. This should fix the problem.
I have the same problem with my stock XJ, the tail, brake and hazards work, but the blinkers fritz out because they are ground dependant in order to blink, for some strange reason the hazzards arent.
This has been my experiences with this problem.
HTH
P.S. check if the hazzards blink at the same time front to back, I worked on a land cruiser that had been wired wrong so that the lights would blink on when the others would blink off, a good helping of hard work(8 hrs for 4 friggin lights to blink "right"!!)fixed the problem.

 

[Mike L]

Don't you have to run one of those trailer wiring kits to combine the stop and turn into one light?

-Mike

 

[RCP Phx]

Don't you have to run one of those trailer wiring kits to combine the stop and turn into one light?

-Mike

You are correct,the XJ has separate bulbs(filaments) for all the functions!

 

[BrettM]

it wasn't a problem with the ground, I wired that back up and no difference.

I'll go check the parts store for a trailer wiring kit, does anyone know if there is an MJ (or XJ) specific one? I'm not finding much in a Google search...

 

[RCP Phx]

Yes,they are application specific.They plug into your existing wiring harness behind the spare tire!

 

[Mike L]

I wonder if you could run two of them. One for taillights and the other for a trailer. I don't think there is a problem, but I've never tried it. Has anyone? Thanks.

-Mike

 

[BrettM]

I went to the parts store today and looked at a bunch of those convertors. They didn't have one for a Comanche, or even pre-91 XJs. They did have several generic convertors, but they didn't seem like they would work, they all converted from 5 wire to 4 wire:

vehicle side:
-ground
-left turn
-right turn
-tail
-brake
converted to:
-ground
-left turn
-right turn
-tail

the problem is that like I described above, the MJ only has 4 wires to start with (5 including backup, which we're ignoring here).

any more ideas?

 

[BrettM]

come on guys, nothing?

 

[WrenchMonkey]

If you disconnect everything, do the front signals work like they should?

Assuming that, I'd run the taillight/brakelight leads into the cab and test em one at a time with a meter to verify they all do what I think they should, again, with the lamps disconnected.

I'd check it with em disconnected because:

Short version: The internal resistance of the new lights might not be what your system's looking for.


Long-winded, break it down ScoobyDoo-style version: As I understand it, the flasher operates on current and heat. The more current, the quicker it heats, the faster it flashes.

The current is based on the voltage and the resistance. (Sorry if I'm oversimplifying) You need a certain amount of resistance to get the right current, to work the turn signals.

If you're now applying the same 12 volts to two filaments in series (connected end-to-end, without branching off) you could very well be doubling the resistance in the circuit. This would in turn halve the current.

I've read that the guys running the LED's have the same problems in the opposite direction: the LED provides too little resistance, producing too much current. I've heard they can work around it using the hazard flasher, because it's less resistance-sensitive. (But I'm not sure how or why)

[end long version]


If I'm right, and it is the resistance throwing it off, is there a way to put each line through just one bulb? Leave one filament in each bulb unused? Might be worth trying, especially if they all check right with the lamps disconnected.

Hope this helps, but if not, I hope it doesn't leave you more confused than before...

Robert

 

[WrenchMonkey]

(Bad ass rig, by the way...)

 

[Jeepkid444]

hey do oyu have any pics of your rig witht he tube bed?

 

[WrenchMonkey]

hey do oyu have any pics of your rig witht he tube bed?

Follow his link, go to the bottom of page four...

Robert

 

[BrettM]

the front blinkers (and dash indicators) do not function properly now either. i've read about the resistance problems with LEDs and figured this might be something like that, but I have no clue where to begin. I might just try to incorporate the stock tail-lights into my bed design

 

[Matt S.]

bret.. I am not all tooooo familiar with Mjs. did they have a seperate turn signal? Or was it a Stop/Turn combo lamp? Depending on what you have, I cant tell in your post. You dont have a resistance problem in the flasher unit. LEDs do not effect your years like they do some others. I will PM you more info.

Matt

 

[RCP Phx]

Heres what I got out of my Haynes manual(diagram not year specific).
Left side:#71 Brake-Blue w/ tracer
#72 Tail-Blue
#75 Reverse-Brown w/ tracer
#78 Left turn-Brown
#99 Ground-Black
Right side:#71 Brake-Blue w/ tracer
#72 Tail-Blue
#75 Reverse-Brown w/tracer
#79 Right turn-Brown
#99 Ground-Black

 

[WrenchMonkey]

the front blinkers (and dash indicators) do not function properly now either... I might just try to incorporate the stock tail-lights into my bed design

Okay, so if you go back another step and actually hook the old lights back up, everything still works? Couln't you then just go back and say, "Okay, these two wires run across this bulb, and those two across the other..."

bret.. I am not all tooooo familiar with Mjs. did they have a seperate turn signal? Or was it a Stop/Turn combo lamp? Depending on what you have, I cant tell in your post. You dont have a resistance problem in the flasher unit. LEDs do not effect your years like they do some others. I will PM you more info.

From his description of a four-wire system, I figured it had to be a stop-turn combo, like a trailer, not an XJ.

Not to be nosy, but I'd like to see what you guys come up with. Maybe I was off the mark, but it's got my curiosity going now...

Lemme know...

Robert

 

[WrenchMonkey]

Well... any progress?

 

[BrettM]

well since the blinkers kinda work (have to tap it repeatedly) I've been driving it as is. I've been too busy getting other projects done and going snow wheelin that I haven't gotten to it. I go back to school on tuesday, so I'll have to figure it out in a couple months. Phil (Weeks) has a pair of stock tail-lights for me, I might try to see if I can incorporate those into the flat-bed.