Hi all,
The illumination for my instrument cluster works normal, until I turn the headlights on. Then they just go black. Not illuminated at all. And its not just the cluster, the illimunation on the radio goes out too.
Is my headlight switch bad? I didn't really dig into it yet. Just drove it for the first time since getting parked for the winter.
Thanks,
-Kyle
Try wiggling the roller for dimming the instrument lights, see if they light up at all. It's probably worn or dirty contacts in the roller
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Hopefully you can see the pics I attached above this sentence. I'm trying to send links from my Flickr account via my phone.
Flickr is NOT mobile friendly at all.
Your issue is almost assuredly the switch. The little metal tab that connects to the switch housing and rubs on the rheostat dimmer wheel has a tendency to snap off on these switches. The pics are a troubleshooting page and 2 pages of pinouts and tests for the switch to include testing for your exact issue.
Lemme know if you can or cannot see them. I'll get on the laptop and work magic from there if I have to in order to make the pictures visible. Yeahhhhh, edited for viewing through my Laptop. Could not get it to work on my phone. Not the forum's fault at all. All blame is on Flickr.
If your switch IS in fact no good find an NOS one on Ebay. The aftermarket parts store ones are WAY overpriced. You can usually find NOS Ebay ones for around $30 USD. I think AutoZone wanted over $100 for a Duralast brand one the last time I checked....
NOS one is here and has the part number:
https://www.classiquecars.com/thunderbirdelectrical80s.htm
Holy hell they are expensive so hopefully you can find one alot cheaper.
Thanks for the trouble shooting diagram. Mine failed Step 5. The B2 -> I Connection. Otherwise, it passed all the other tests. Guess that means I need to pull the cluster to see where that I circuit leads.
Check fuse 13.
Added some notes to the wiring diagram.
Update: Fuse 13 was popped. Replaced with a new 5amp fuse. Repeated the test above, and it still fails that step 5.
I'm thinking this might be an issue on the backside of the cluster.
Did the fuse blow again?
No it didnt. When jumping the I -> B2 connection the radio lights up, as it would when you turn the headlights on. But the cluster is still dark.
From your 1st post: The electronic gauges (LEDs) turn on with the ignition switch. That's good.
When you turn on the headlights, the "cluster illumination relay" switches the electronic gauges power to the headlight switch dimmer circuit ( fuse 13). This doesn't work.
The B2 to I jumper test should only turn on the illumination lights that come on with the headlights, not the electronic gauges (because the cluster illumination relay stays in the ignition switch power position).
All the stuff on circuit #19 LB/R wire in the diagram I posted should turn on.
Note: The B2 terminal of the headlight switch is labeled A in the wiring diagram.
If you plug the headlight cable harness back into the switch, will the electronic gauges now work with the headlights on?
Nope, when I plugged the headlight switch back in, key on, turn the headlights on, the cluster is still black. And the fuse doesnt pop. Think I'll pull the cluster this week, since Ive had issues with it before.
I just started to have the same issue on mine. I replaced the headlight switch and the electronic cluster goes dim when the headlights turn on.
hi everyone,
I dove back into this issue and I made a discovery: the headlight switch gets really hot. Like hot enough that the coil for the rheostat was glowing. I'm not a genius, but if its getting that hot, that means its pulling a lot of current. So guess i'll be ordering a new headlight switch.
That'll help for the short term, but you should consider modifying the lighting system to have power for the LO-HI beams run through a couple relays, instead of through the switch.
The electronic cluster is on full bright with the headlights off.
With the headlights on, it is adjustable with the dimmer control.
The rheostat is the dimmer control. Drawing that much current, you should be blowing fuse 13 again.
Just turn the parking lights on. This will get the headlights out of the picture and still power the dimmer control.
Pull fuse 13. Does the rheostat still overheat?
If not, are you sure that fuse is only a 5 amp?
They do! I have 2 relays mounted in the engine bay. They get signal from the headlight switch, and draw power directly from the positive terminal of the battery.
Sorry, my post wasn't very clear. What I meant to say was that my dash lights are doing the same thing. I replaced the switch thinking it was bad, but it is doing the same thing with the new switch, full bright with the headlights off and then goes dim when the headlights are turned on.
Does moving the dimmer thumbwheel change the brightness when the headlights are on?
Unfortunately not, when I turn the dimmer switch wheel the lights remain out. It only happens when the headlights are turned on, when they are off the digital instrument cluster is fully lit.
Sorry, I thought when you said the cluster was dim you meant on but not bright.
If none of the dash lights up with parking lights or headlights on, check fuse 13.
See post 5 in this thread for the fuse panel diagram.
Update to my situation:
Bought a NOS headlight switch.
With the LED 194s in the cluster illumination, it will pop fuse 13 when I turn the parking lights on and/or the headlights.
When I put incandescent 194 bulbs in, the fuse doesnt blow, but the cluster doesnt light up with the headlights on. It still lights up with the key on.
Any thoughts? Could it be something in the cluster? Because the fuse doesnt pop with the headlights ON and when theres no bulbs in the illumination sockets.
1. Do you have a test light? If not get one.
2. Do any of the dash lights come on with the headlights/parking lights?
The fuses have two test points that can be probed with a test light.
No power to either test point: Problem is upstream from the fuse.
Power to just one test point: Fuse is blown.
Power to both test points: Problem is down stream from the fuse.
The test light probe is sharp enough to pierce the wire insulation for further testing.
So I shouldve been more clear: When I turn the headlights ON: the cluster goes dark, the radio goes dark, and the climate control display goes dark too. And based on the wiring diagram you provided, they all share a ground?
With the headlights ON, the turn signal still lights up in the cluster. So does the High beam indicator.