I have a 78 f250 ranger custom with a 400m. Ignition off and lights on I have gauge lights. As soon as I turn ignition on the gauge lights turn off. Then ignition on lights off gas gauge works fine, as soon as I turn lights on with ignition on the gas gauge pegs. This has got me lost. Brake light, seatbelt light and blinker lights work on my cluster. Any ideas where to look?

 

The only place where these three things you mention have any interaction is the back of the instrument cluster along the printed circuit, or along the cluster connector and associated wiring. Most likely there is a short nearby, or the cluster has lost ground. You'll have to pull the cluster forward and see if anything seems out of place.

Once you do that, the first thing I would do is check for continuity between the instrument cluster voltage regulator (ICVR) body, and true ground behind the dash (exposed metal) with the cluster hooked up. This will prove out the cluster ground, which would be my first suspicion. You cannot check that without a multimeter; meaning you must have one to troubleshoot this problem.

There aren't any recent modifications or electrical work you're leaving out of your description, right?

 

Im not sure I just picked this truck up it had an aftermarket stereo which I removed. When I first got it the truck didnt even have a fuse in it for the cluster. I will try to take pictures of what I find when I take the cluster out. Last time I checked I did see a black wire not hooked to anything and 2 brown wires that go inside a round connector not hooked up to anything.

 

The two BROWN wires terminated with a bullet connector are simply a parking light tap; it's supposed to be there and unconnected.

If the BLACK wire was terminated with a ring terminal such that it would normally screw down to a metal surface, then yes, that must be connected. If it was terminated with a bullet connector similar to above, it's probably actually a BLACK with BLUE stripe wire from the courtesy light circuit, and is simply a tap that is left alone.

 

Thats what I found

 

Please refer to my first post for the instructions I've asked you to carry out with regard to troubleshooting this problem.

 

I will once I get home from work. Pictures were something I did on break. Dash cluster circuit is ripped in one of the pics. I forgot to mention that the temperature gauge doesn't work. Where is the sensor located on a 400m? Thermostat is in front of the intake in the block.

To correct my first post blinker lights stay solid green besides when blinking, fasten belts light stays on and oil light comes on around corners. No other lights work with ignition on. With ignition off only half of the cluster lights work.

 

This picture is too blurry, but it looks like it may actually be BLACK with BLUE stripe. If so, you'll have an issue with the dome light. At the very least, it should be taped off to prevent a short.



This is fine. It's the parking light tap I mentioned.



This is the radio connector. Someone cut the YELLOW with BLACK stripe hot-in-accessory wire running to it. That wire should be tracked down and taped off, but it won't be related to the problem.



It's hard to tell from the picture, but it looks like a trace is shorted. This printed circuit needs to be replaced regardless. Whether or not this is related to your problem depends on which trace this is and which bulb is getting shorted.

 

Ok I will order a new circuit board and do the checks for you as soon as I can. Next to the radio plug is another blue wire with a red stripe I believe, what is that for?Dome light doesn't work but if that wire fixes it then I will hook it up, is it ground or a hot?

While im fixing all this wiring issues I would like to upgrade dash lights to led so they are brighter. Are those plug in and go or do I need to wire those in? If you know of a part number for the led I would like to order some. I bought this truck for a pulling truck but now I love driving it so might have to buy another. Heres a pic of it, I need to find a new box for it.
Sorry if pic is small im using my phone.

 

Here's some sites for lights. I bought the kit from Hipo parts and it works well.

LED Brake Light, Turn Light and Tail Light Bulbs | LED Car Bulbs | Super Bright LEDs

1961-79 Ford Truck & Bronco LED Gauge Light Conversion Kits - HiPo Parts Garage

 

BLUE with RED stripe is dash illumination.

You'll need to confirm the jacket color of the bare wire for me to answer your other question, and describe where it's coming from.

 

Looks like blue with red or orange stripe next to the radio connector.

 

Could that be the wire for the radio light? The connector for the radio has the same wire and a yellow one.

 

For whatever reason, I'm not able to open a larger version of that picture.

As I said before, BLUE with RED stripe is dash illumination. What I did not make clear, however, is that the radio dial is part of dash illumination. The radio pigtail has two signals: BLUE with RED stripe to illuminate the radio dial along with the rest of the dash, and YELLOW with BLACK stripe for accessory power to the radio. The radio grounds through its chassis.

What I have described here is separate from your question about the dome light and your bare wire. I'm looking to you for clarification per my last post.

 

The bare wire in your previous post the first picture looks solid black to me. I will get a light and triple check it. The pigtail has the blue wire with a stripe and the cutoff yellow with strip wires. The blue wire with a red or orange stripe is laying next to that pigtail not hooked to anything in my last post.