So i'm in the process of swapping out my gauge lights in my 1990 F-150 5.0 to make them blue LEDs (brighter, plus the blue makes the gauges a nice aqua color). I already had to take the gauges out (E-brake bulb was dead) so while I was at it I decided to clean the gauges and clear plastic cover, and swap the gauge lights out. The gauge illumination lights were the only ones I was going to swap, all the warning lights and turn signals are staying incandescent.

I got the lights installed, put the gauge cluster back in, and they didn't come on at all. I turned the dimmer all the way up, still nothing.

I figured I had the polarity wrong, so I went through, checked the lights to determine their polarity, and tracked down the grounds for each of the 5 bulb connections and put them in correctly. Put it back together, and still nothing.

The other lights in the gauge cluster work, as do the gauges themselves, so it's not the harness connections.

i've got some LEDs in other parts of the truck. Under hood light, dome lights, cargo light, and glovebox. The bulb in the glovebox is the exact same as the one i'm trying to install behind the gauges, and it works fine. I remember reading something when I was looking into the swap about wiring a resistor in (was talking about the gauge light swap specifically, for my series truck. of course I can't find the website now...) but if it needed that, would it not need one for the glovebox light too?

The one other thing I can think of is my dimmer/headlight switch might be bad. When the incandescent lights were in there, If I turned it all the way counterclockwise (right before the click to turn on the cargo/interior lights), then a few degrees back clockwise, the gauge lights would come on bright. A few more degrees, and they cut off, keep turning it clockwise, and they start at dim and work their way up. Along the way they cut out once or twice, then if you turn it all the way clockwise till it stops, it cuts out again.

Any ideas on what I might be able to do to get this working, or if i'm even going to be able to?

 

Update:
I swapped out the headlight switch, which definitely was bad.

Then I went through with the 9 volt battery that i used to determine polarity, and found that none of the lights were lighting in their individual sockets. I pulled the lights and discovered that the contacts are closer together on the plastic LED housings than they were on the original glass ones, and weren't making a connection. I bent them outward, and reinstalled them.

Now they work great, and they even can use the dimmer function. I read that some lights required the dimmer to be al the way up, of they wouldn't cut on at all, but these seem to go through the full range just like the stock lights.

Ill post some pictures when I get my phone fixed and can take them

 

For your info, the resistor is added only to the turn/brake lighting when they are changed to LED. This makes the turn flasher work correctly and gets rid of any "ghost" voltage that might be present on the brake circuit, which will not light the regular bulbs but will light the LED brake bulbs.

 

That must be where I saw it, because I had looked into that too. I kind of got scared off on swapping the brake/turn lights though, because people saying that it wasn't DOT approved or safe. I also had planned on removing my cargo light housing and replacing it with a 92-96 LED CHMSL light, but someone said that no resistor could cause shifting problems in the automatic transmission. I don't know why it would, or if that's true, but that worried me also.

Would it be the same resistor to make the turn signals work and not mess with the transmission, or would it be two separate ones?

Thread where that was discussed: https://www.ford-trucks.com/forums/1...fferences.html

 

You can probably get away with it if you don't go ALL LED's in the brake circuit. If you change the high mount to LED but kept the old timey bulbs in the back, then you would probably not have any problems. The old bulbs present enough load on the circuit.