'88 Headlights acting weird.

[Hoosierman]

Hi all, recently I introduced myself in another section of the forum. My '88 Custom over the last couple of months has been giving me fits with the headlights. So occasionally the low beams wouldn't work, but the high beams would. The dimmer switch seemed to have an off and an on position, nothing in the middle. Well a few nights ago while driving home, low beams refused to work and have since. No problem, I've heard of this issue. I had the dash pretty much open due to a few minor fixes I was doing and replaced the radio and such. So while I was at it, I just replaced both the dimmer and the switch since I had no clue how old they were.

Still no low beams. What would be the next practical step to take with this? Were these years of Rangers/BIIs known for electrical issues at all? I mean, statistically speaking, the odds of both low beams in sealed beam headlights going kaput at the same moment are not likely at all. I did notice that in the headlight switch, the connector for the brown (ish) wire on the pigtail was melted slightly, but the connector still mated properly. That's about it... Thanks.

 

[RonD]

I don't think Rangers had "Flash to Pass" in 1988 but not sure

I have 1988 wiring diagram for light switch, page 1 is the one you want

Looks like both high and low beam get 12v from the same wire out of the main light switch, a red/yellow wire to Multi-function switch(aka Dimmer switch)

So if high beams work then the fusible links are OK, and the main light switch and the red/yellow wire as well

Brown wire looks to be for Park lights, exterior lamps

I don't have the head light wiring

You could unplug a head light and test for 12v on low beam
Generally 3 wires
Ground, shared
High beam 12v wire
Low beam 12v wire

There will be just 1 wire out of the multi-function switch for low beams, it usually splits at the front of vehicle and is shared by both head lights
Same for high beams

 

[franklin2]

Headlight switch feeds power to the dimmer switch. So if your highs are working, that means the headlight switch is sending power. You need a testlight to see if you have power after the dimmer switch in low position.

 

[Hoosierman]

I tested a headlight plug and I get the standard 12-ish volts on high beam, but nothing on low beam.

 

[RonD]

Get the wire color of the no 12v wire
And do what franklin suggested, see if you have 12v at the dimmer switch on that color wire

 

[Hoosierman]

Well I had a little time today to test the R/B wire on the dimmer switch and it appears to have 12v when the low beams are engaged.

 

[RonD]

But switch is not passing that 12v to the low beam wire, just the high beam wire, so bad switch

 

[85_Ranger4x4]

I don't think Rangers had "Flash to Pass" in 1988 but not sure

No, pull it back for dim, pull it back again for high. It just toggles between the two settings.

 

[Hoosierman]

No, pull it back for dim, pull it back again for high. It just toggles between the two settings.

Okay, I know it's extremely possible, and it has happened before but I have to ask-- What are the odds that the new dimmer switch is defective straight out of the gate? It's a Standard Motor part, which I have had very good dependability from as a brand.

My original thinking was, if that's the same R/B wire coming out of the dimmer switch that I'm tracing to the headlights, could it not be something between the dimmer switch and the plug that caused this?

I'm only asking to cover the basis here.

 

[85_Ranger4x4]

I would have 0 faith in a Standard byproduct... but I would check your connections though. It came and went, nothing changed with new switches... and we have 40yo wiring at play.







You can see the wiring sneaking along the inside of the driver side fender in figure two.

 

[RonD]

Unplug the dimmer switch and use a jumper wire between the 12volt in from main light switch(turn it on) and to the OUT to low beam wire
That is what the dimmer switch does

On the diagram it looks like red/yellow wire is IN from main light switch, and red/black wire is OUT to low beam bulbs

 

[Hoosierman]

Unplug the dimmer switch and use a jumper wire between the 12volt in from main light switch(turn it on) and to the OUT to low beam wire
That is what the dimmer switch does

On the diagram it looks like red/yellow wire is IN from main light switch, and red/black wire is OUT to low beam bulbs

I would have 0 faith in a Standard byproduct... but I would check your connections though. It came and went, nothing changed with new switches... and we have 40yo wiring at play.






You can see the wiring sneaking along the inside of the driver side fender in figure two.

Hey that helps, it confirms what I traced earlier! Much appreciated!

Okay if I'm understanding the suggestion correctly- establish a connection from the R/Y wire to the R/B wire, essentially bypassing the dimmer switch, to test the low beams. That's the basic idea here, right?

I'm more new to electrical than I am to mechanicals- but I love this stuff!

 

[RonD]

Yes, that's it

Electrically you are doing what the switch does, should do
Connecting R/Y to R/B

If still no low beams then wire from switch to bulbs is the issue
I would just run a new wire if that's the case
Trying to trace a wire thru the firewall and inside harness's is very time consuming and not as rewarding as you might think, lol

 

[RobbieD]

Do the jumper like @RonD suggests and see what you have.

There's only one connector between the dimmer switch and the headlights- that's C120, on the driver fenderwell and shown in figure 2 (and in the wiring diagram). If you do have +12V on Red/Black at the dimmer switch with low beams on, then next see if you have the same voltage at C120. The splice in the wire is at the driver headlight connector, so that would be the next point to test for low beam voltage. You basically test your way down the circuit until you locate where it changes from "good" to "bad".

And, you don't have the light monitor display, right? A Ranger Custom should be the base model. If you do the lights out display, that's a somewhat different animal.

 

[Hoosierman]

Do the jumper like @RonD suggests and see what you have.

There's only one connector between the dimmer switch and the headlights- that's C120, on the driver fenderwell and shown in figure 2 (and in the wiring diagram). If you do have +12V on Red/Black at the dimmer switch with low beams on, then next see if you have the same voltage at C120. The splice in the wire is at the driver headlight connector, so that would be the next point to test for low beam voltage. You basically test your way down the circuit until you locate where it changes from "good" to "bad".

And, you don't have the light monitor display, right? A Ranger Custom should be the base model. If you do the lights out display, that's a somewhat different animal.

Will do!
When I have sunlight of course... To answer your latter Q: I very seriously doubt that I have a lights out warning on this rig, I've never seen one. The only light I ever see come on is the brake light and it does that randomly in shifting from gear-to-gear, my understanding of it is that it has something to do with not having functioning parking brakes anymore- but that's a different issue.