RPM’s rise significantly after turning headlights on

[Malleus]

So I would try the troubleshooting chart in the Engine section. HTH

 

[gummycarbs]

Forgive me if this is a dumb question, but where would I find the connection point to disconnect the module?

It's not a connection point, sadly. It's a port- or dealer-installed unit. It's behind the rear, passenger side plastic, probably zip tied to the wire bundle that goes to the taillights. Mine was installed with those awful 3M Scotchlok connectors.

 

[blkprj80]

@Malleus Isn't that the ground point "ID" down there in the lower right corner? If I follow it back, it is the ground for the voltmeter, speedo, fuel gauge, and tach. Some of those needles are damped, I imagine, and therefore wouldn't jump. By the way, THANKS for posting the diagrams, it helps a lot! Especially where an LX450 is not the same.

And @Chachi254 , to disconnect your trailer module, look behind the right rear side panel (subwoofer). There should be a module there that plugs in-line with your taillight harness. Disconnect the module from both directions and return the factory harness to normal by plugging the two OEM connectors together. You don't need this unless you tow, and if you do, go buy a new one and reinstall it. Old ones just shouldn't be trusted. This could very well be a part of your troubles.

Back to your original post: When you say "turned on the headlights", may I assume you went from a fully off state, not park lights? It would be interesting to see what happens with park lights only. When you "turn on the lights", the dash cluster gets fed lamp power too. Play with the dash illumination knob thingy.

My fear is that you'll wiggle a wire and things will go back to normal. For a while. Then again some day.

I don't see that the fault is apparently in the combo meter (at least I wouldn't look there first):
View attachment 1625569

 

[Malleus]

@Malleus Isn't that the ground point "ID" down there in the lower right corner? If I follow it back, it is the ground for the voltmeter, speedo, fuel gauge, and tach. Some of those needles are damped, I imagine, and therefore wouldn't jump. By the way, THANKS for posting the diagrams, it helps a lot! Especially where an LX450 is not the same.

And @Chachi254 , to disconnect your trailer module, look behind the right rear side panel (subwoofer). There should be a module there that plugs in-line with your taillight harness. Disconnect the module from both directions and return the factory harness to normal by plugging the two OEM connectors together. You don't need this unless you tow, and if you do, go buy a new one and reinstall it. Old ones just shouldn't be trusted. This could very well be a part of your troubles.

Back to your original post: When you say "turned on the headlights", may I assume you went from a fully off state, not park lights? It would be interesting to see what happens with park lights only. When you "turn on the lights", the dash cluster gets fed lamp power too. Play with the dash illumination knob thingy.

My fear is that you'll wiggle a wire and things will go back to normal. For a while. Then again some day.

The way I read the diagrams, "1D" grounds only the fuel and voltmeter. The speedo and tach are grounded through the combo meter. I could be wrong, I haven't looked that closely at it. Yes, you're correct about the damping; IIRC they have springs on them. I have two out on my bench right now. I need to swap the trip-o-meter in mine for one that works. I'll look when I pop the meter open.

 

[Malleus]

It's definitely worthwhile to have the vehicle specific EWD. Unless you have the wiring cold in your head, there are subtle differences that would really screw up a good troubleshooting plan.

Here's what I meant about the combo meter grounds:

Each of the four connectors have a ground lead in them. Some components are grounded through the harness/connector, some are routed to a nearby body ground. I haven't looked that closely to figure out why.

 

[Chachi254]

Okay, did some investigation last night and came up short on finding the culprit.

1) disconnected the trailer harness module and reconnected original wiring to bypass the trailer lights module. While looking behind the pass-rear panel, I also checked all other connections and they are fine.

2) took off the PS Kick panel and checked every connection but had no burnt connections and the ground wire connection was solid.

3) I checked for leaks from the windshield and roof and there are none. This vehicle is tight from the aspect of leaks. There are no leaks present.

4) I found a few very corroded connections coming pff of the passenger side engine bay in-line with the cruise control (photos below)

5) I also found a corroded connection under the rear of my car, right above the spare tire. I disconnected the plastic connector and reconnected.

6) All fuses are okay

7) There are 0vdc from negative of battery to ground connections.

 

[CJF]

This may or may not be a related symptom, but I’ve been having some weird electrical issues as of late where my cruise control doesn’t work when my headlights are on, pressing the brake turns on my dash lights

Those (plus the TC disengaging with the headlights on) all suggest some sort of intermingling of the the headlight circuit and the brake light circuit.

 

[Malleus]

Those are nasty. Try this:
CRC QD 11 oz. Contact Cleaner-02130-6 - The Home Depot
https://www.permatex.com/products/l...ricants/permatex-dielectric-tune-up-grease-4/
I use both every time I disconnect a connection that I haven't previously cleaned.

 

[Chachi254]

Fixed! (Mostly)

Following a good cleaning/greasing of the connectors in the photos I posted above (along with every other connection underhood), I found that my issue wasn’t resolved fully resolved...

But then, after fiddling with my twilight bulbs for the 900th time this week, I realized that I had put accidentally put 1157 bulbs in the 1156 sockets and 1156 bulbs in the 1157 sockets. The 1157 bulbs had their connection nubs sheared off on one side. Once I got new (and correct bulbs), greased them, and reassembled, my cruise control, dash light/brake pedal, and headlight/cruise control issues have gone away!

The only issue remaining is my radio display light turns off once I put the car in drive or turn the headlights on.

I feel so stupid that I missed the bulb issue that many times. I hope you all don’t feel that I wasted your time I honestly think that the corroded connections in addition to the mismatched bulbs caused my problem.

I can’t thank you all enough for all of your help. I hope this feed will help others that might be in the same spot!

 

[Malleus]

This may help:

EDIT:
You can see that all the center panel illumination is common. Green wire in, White/Green wire out.
Here are my connectors, for reference (this is a '95 Land Cruiser, but this wiring is common):

 

[Malleus]

Check to see whether or not the antenna switch works when your radio lights go off. I am assuming here that you have the factory stereo.

Also, you should have a light in the ashtray, when your radio lights are on.

 

[Chachi254]

Check to see whether or not the antenna switch works when your radio lights go off. I am assuming here that you have the factory stereo.

Also, you should have a light in the ashtray, when your radio lights are on.

Correct, I do have a factory stereo. With the headlights on and off, and in Drive, the antenna motor works just fine. I also tried the hazard lights, rear defrost, rear heat switches, and made sure my cigarette lighter power is working, and they all are functional regardless of what gear I am in or if my headlights are on or off. I confirmed that my antenna motor does not work when my radio is on cassette Mode, if that narrows down anything haha.

 

[Malleus]

I meant the ashtray light, not the cigarette lighter, that's on a different circuit.

That sounds like a body ground fault, on the kickpanels (1D & 1E):

It may not be at the ground screw, but in a connector somewhere. You'll have to trace the circuits until you find it.

 

[Chachi254]

I checked and the ashtray light is fully functional when the headlights are on and turns off when the headlights are off. Opposite of the radio light operation.

I’ll be working on the 80 tomorrow and will see if I can pinpoint the connection error.

Thank you again for your detailed help. You’re the man.

I meant the ashtray light, not the cigarette lighter, that's on a different circuit.

That sounds like a body ground fault, on the kickpanels (1D & 1E):
View attachment 1626502

It may not be at the ground screw, but in a connector somewhere. You'll have to trace the circuits until you find it.