OD light not working

[ratdude747]

Here's the problem: My "OD off" light was getting flaky over the past month or two (sometimes it would work, sometimes not) and now it has quit working entirely.

First, it's not blinking; my tranny was rebuilt in October 2014 and the transmission shifts fine.

I did LED my instrument cluster; when I did the mod, the light was working (faint glow when off, bright when on). Now,when the light isn't working, I get no glow or anything.

Yes, the button does actually enable/disable OD. It's just the light that isn't working.

I attempted some diagnosis work. First, I made sure the LED module was making good contact to the bulb holder, and that the holder was making good contact to the circuit board (well, circuit flex plastic whatever). I then did some probing, and traced the circuit to a the switched positive input (pin 1 on the big connector), white wire with green stripe, and a common ground (shared with the 4x4 lights and the cruise control light, none of which my truck uses) that was on pin 4 or pin 5 (next to the vacant pin for the cruise control light), orange wire with a black stripe. The O/BL wire wasn't showing continuity to ground, even with the engine on. Open circuit, I was getting battery voltage to the W/G wire, with about 0.2V difference when the OD was on/off (which being a current sourced input, would make sense). However, manually grounding the LED with a test light (incadescent 12V bulb with wires on the end) did not cause it to work, which may have been an issue with my testing, not the wire.

What I need to know is where that orange/black wire goes... sadly the OD light isn't on any wiring diagram I have access to. It seemed to go towards the fuse box or firewall connector (which would then go to the power distribution center?).

I hope my PCM isn't hosed... This truck did bomb an ABS computer not that long ago (when I bought it or right after, August 2014), fried input on the controller chip (brake fluid sensor input) so it is possible that some sort of an overvoltage/ESD event took it out.

Where to go from here?

 

[ratdude747]

Found an orange/black stripe wire at the PCM connector. I tried reseating the connector and verifying that my two grounds at the bulkhead (one for the PCM harness, one for the engine block) were good. No dice.

I really need a wiring digram here... nothing shows this damn light, nothing.

edit- not quite what I need, but I did find one for the 1997 4.0, which at least gives the white/green wire's location; it's going to PCM pin 79:

http://www.diakom.ru/CAR/Ford/1997/Ranger/SYSTEM WIRING DIAGRAMS/15634.pdf

Granted, that's the 5R55e, not the 4r44e I have (and wrong motor too, obviously)... but that's one of the wires. However, the orange/black wire isn't shown... so the saga continues to find where it goes.

 

[ratdude747]

Yahtzee!

http://www.diakom.ru/CAR/Ford/1997/Ranger/SYSTEM WIRING DIAGRAMS/

all of the 1997 wiring diagrams. changing the 1997 to a 1995 didn't work, but this ought to do. I might go ahead and download all of them since that shit is sorta hard to find (and may not be up for long...

edit- well well well.... I had the wires backwards I guess, as the orange is the light supply, which comes from the headlight switch. A while back I did some splicing in that area as my headlight switch failed and melted to the pigtail. I wonder if that splice failed.

 

[ratdude747]

Fixed.

The issue began by my not plugging in the headlight and dimmer switches. As a result, the orange/black wire wasn't connected to anything. Thus no power (and a wrongly assumed ground path). Second, due to the resulting misunderstanding of the light circuit, I assumed incorrectly which side was ground, and installed the LED backwards. Thus, once put back together, it didn't work. Flipping the LED fixed the problem; my splices were good.

It makes sense now, as all of the lights on that circuit are ones that could be on for long periods of time w/o being a cause for concern (4x4 status lights, OD off light, cruise control light), hence why it would be sensible to feed them off the dimmed illumination circuit and switch the ground side.

I feel really stupid... At least I discovered a handy bit of wiring diagrams.