E4OD TC engagement

ISPKI

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The running lights shouldn’t be an issue. And like I said, adding an incandescent in parallel to each brake/turn circuit should fix that part of the equation. You could mount a cheap trailer light under the bed, and get some cool “under glow” like all the kids have.
Heh, I was actually going to mount lights around my rear bumper setup since it houses my crane and outrigger and sticks out quite a couple feet from the rear of the bed. Cant tell you how many times ive dinged my knee on the corners of that thing working around the truck at night. More underbed lighting would be nice too since my logging straps wrap under the bed and hook onto rings underneath. Being able to actually what im doing under there would be nice.
 

Black dawg

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The normal part of the lockup circuit wont function without regular bulbs in there. See this all the time. Also wont function if there is no connection to the bulbs, or they are burnt out. Have no idea why they made the converter lockup independently of the normal circuit with a certain amount of throttle opening, but all of them I have driven are that way.
 

ISPKI

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The normal part of the lockup circuit wont function without regular bulbs in there. See this all the time. Also wont function if there is no connection to the bulbs, or they are burnt out. Have no idea why they made the converter lockup independently of the normal circuit with a certain amount of throttle opening, but all of them I have driven are that way.
Thats crazy. Something as critical as the transmission function should be on it's own circuit.

Does anyone have any idea what the circuit resistance should be? My truck had a fiberglass utility body on it and the circuit has been heavily modified. I have it cleaned up really well with connections made inside sealed junction boxes but id like to dial the resistance in to a correct value, or close to it.
 

Big Bart

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ISPKI,

Let’s see what comes back but some thoughts.

1) I would use a ohm meter on two standard bulbs (Three if you have a 3rd brake light on top of the cab.) in a light socket to get your overal resistance. Then test some resistors for a match. (Or use two resistors to get the resistance you want.) Then test drive, perhaps add a resistor if the tranny is still not seeing the brake signal resistance right.
2) Or as stated above just add two standard brake light sockets and bulbs near your junction box. Paint the bulbs black to avoid the light if it bothers you or weld up a little box and attach to the frame or bed to keep them dry and out of harms a way.
3) Or replace your brake lights on the bed with standard bulb fixtures.

As always send a few pics and let us know how it works out.
 

TNBrett

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I’m not an expert on this by any means, but my understanding is that the control module just needs to be able to sense or “see” a path to ground on the brake light circuit when the brakes are not applied, and then “see” 12v when the brakes are applied. This is normally accomplished with the filament of the bulb. A resistor should do the same thing for you, and I don’t know that the value is all that critical. I imagine an “led taillight resistor” from Amazon or the like would fit the bill. As far as why, I have to assume it was the easiest way to achieve some form of logic from the module. Presumably, the engineers responsible for it in the late 80’s never imagined that a time would come when incandescent bulbs would be on the edge of obsolescence and LEDs would be their replacements.
 

ISPKI

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So ive done yet more research on the issue and it isnt stacking up, the TCM should be able to send a signal thru either the LED or the filament. Maybe it is sending a signal out at all times and it does NOT want to see the signal complete it's circuit until the brake lights are applied. If the signal current is low enough, it may never overcome the resistance in a filament bulb and thus never complete but if the lights are LEDs, then the constant signal is enough to power a few of the LEDs in the lamps. From what ive gathered, an LED does not have a measurable resistance. At the same time, neither does a filament lightbuild UNTIL some current is supplied to it. Then the filament builds resistance as the current supplied increases.

Maybe its possible that the trickle current increases the resistance in the filament to sink the current but is limited in it's supply by the TCM, therefore never making enough to illuminate the bulb.
 

DaveBen

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It is the difference between a light bulb and an LED. The LED is a diode and will restrict current flow compared to the light bulb.(they both restrict current but in a different way) The light bulb will have a low restriction of current compared to the LED. Check your light bulb for resistance in ohms and then check the LED. The LED will be different and that is what the TCM sees.
 

Black dawg

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Never really spent the time to understand why, just always fixed wiring or change back to bulbs and everything works.
 

ISPKI

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It is the difference between a light bulb and an LED. The LED is a diode and will restrict current flow compared to the light bulb.(they both restrict current but in a different way) The light bulb will have a low restriction of current compared to the LED. Check your light bulb for resistance in ohms and then check the LED. The LED will be different and that is what the TCM sees.
Right but from what ive read, neither LED or Filament bulb behave as simply as that. Filament bulbs have zero resistance (I think) until current is applied of a certain level. The more current supplied, the more resistance the bulb has and the brighter it gets. The resistance value of a light bulb should be the value when being supplied with it's rated current (I.E. when fully illuminated). If a source supplies less current than is required to illuminate the bulb, then it should have zero resistance.

LEDs flow zero current until they are supplied with a minimum amount. Once they have the minimum amount, they "open" and allow current through the circuit. They have no resistance except for that of the wire connections but they do have a voltage drop once they open so that makes me wonder if just adding a resistor would actually solve the issue, it seems to be that they wouldnt.

What I wonder is if the LED is being supplied 12V or 12.2V or something, LEDs should cause around a 1.5V drop once on which would cause the circuit to drop to around 10.5-11 ish but since they only require a few volts to operate they would still function.

There may be a two fold issue here. If the TCM needs to send a low amperage trickle current thru the circuit for a sort of signal, and I know it isnt enough to illuminate all of the LEDs because only 2 bulbs actually light up all the time, then maybe the circuit isnt completing because the current supplied is too low.

Second issue may be that the trickle signal may be sufficient to turn on some of the LEDs but the voltage drop across the diodes may cause it to be too low for the TCM to interpret, assuming the TCM is looking for a 12V+ signal, it likely wouldnt get that after the LEDs.

I dont know if my understanding of the resistance of an LED is 100% accurate but that seems to be where my research is leading.

Either way, im looking at a couple cheap filament lights to wire in for side markers. Put them in parallel should give the TCM a clean circuit.
 

DaveBen

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You are right in what you are saying. I was trying to keep it simple with the basic needs of the TCM. This can get complicated. The TCM needs to see current flowing through the bulb and you will not see current flowing through the LED (at least not that the TCM will see).
 

ISPKI

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Well I found a company called Peterson lighting that makes both incandescent and LED versions of truck and trailer lighting. What I am looking at is getting a couple square incandescent amber lights and mount them at the rear corners of my bed and wire them into the stop/turn signal and the running lights. Should look good and get the job done.
 

ISPKI

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You are right in what you are saying. I was trying to keep it simple with the basic needs of the TCM. This can get complicated. The TCM needs to see current flowing through the bulb and you will not see current flowing through the LED (at least not that the TCM will see).
Seems like it already got fairly complicated! But I think I have my solutions for now.
 

nelstomlinson

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Sounds as if you could find that connection from the control module to the brake light circuit, and reroute it to an SPDT relay, which would connect it to +12VDC when the LED brake lights are energized, and connect it to ground when they are not. Or, just put a bulb in parallel...
 
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