Hi everyone,
I have a bit of a headache here. Basically my dash lights don't work.
Here's the rundown: my truck is a 1966 F600 with an oil tanker body. Every light works on the entire truck....front/rear/both sides turn signals work, brake lights both sides work, all the running lights work, head lights high/low work, the dash turn signal indicators both work.
Here's what doesn't work: dash light at very top of speedometer, illumination lights on both sides of the speedometer, illumination behind speedometer, emergency flashers(switch might be broken), and the interior dome light. Also, the fuel gauge, oil pressure indicator, and temperature gauge don't work. Someone installed an aftermarket temp gauge and It does work. I checked all the bulbs and they're all good. I checked the fuses and they're all good. I am an electrician by trade, but I really don't want to go messing around with the wiring under the dash.
Does what I am describing sound like an electrical issue with the 1966 Ford F-series? The Cab components all seem to be identical between the F100 and the F600. Is the wiring the same?
Help please.
Thanks,
Erich

 

Is it grounded? the dash that is. check for good clean ground.

 

The dash lights have a dimmer mechanism at the front of the headlight switch. There is a small brush on the switch that contact a wheel with an embedded spring to adjust the brightness. If that spring or brush break (which is common) your dash lights won't work. Start by turning the **** all the way counter-clockwise, that will set them to max brightness. If they still don't work, you may need to replace the switch. The wire from the switch that powers the dash lights is blue/red (I think) if you want to check for voltage.

 

Thanks guys,
I'll check out those options. I forgot to mention that the horn doesn't work either.
Thanks again,
Erich

 

The horn problem is probably the horn contact brush under the horn ring or button.

 

I figured out that the gauge issue was due to faulty sending units. I replaced the Oil Pressure sending unit today and now the oil pressure gauge is working great.
I am looking for a fuel tank sending unit now.
I have deduced that the dimmer is shot in the headlight switch so I have no dash lights.
the emergency flasher switch is busted too. I bet once I replace both of these witches the dash lights and flashers will work again.
The horn.....someone put a cheapo horn button on the steering column, I can hear it making contact but I think I need a new horn itself. When my truck was repainted they sprayed paint all of the horn itself so I wouldn't be surprised if that did it.
Theres some kind of transformer just behind the horn on the inside of the engine compartment. What is it for? there is a yellow wire with a quick connect coming out of the transformer that is disconnected and there is another yellow wire with the same type of connector that is also disconnected coming out of the wiring harness about 6 inches towards the cab from the transformer. They are both female connectors on these wires...what are they for?
Thanks for your help.
Erich

 

The doo-dad in the engine bay is the relay for the horn. I don't know the wire color coding or pin configuration for it, but there should be a constant hot to that relay. The horn button on the steering wheel grounds the relay to activate it, and the relay then powers the horn. The horn is grounded through it's mounting bracket. There's a good chance that the relay is bad. It's hard to say what they've done with the wiring to it since I believe the original plug for the relay was a molded one piece that matched the pins. You can replace it with a generic relay, that's what I did on mine.

The blue/yellow wire coming out of the steering column is the wire that the factory button grounds for the relay, but it's possible the brushes in the column are bad and that's why they put the cheapo button on there.

I know that sounds confusing but I'll try to clarify anything if you need.

 

Shouldn't there also be a constant hot wire attached to the emergency flasher? The emergency flasher on my 66 only works with the key on which makes it kinda useless.....

 

Yes it should be, someone along the way could have subbed a switched wire in.



John

 

I'll look at the horn relay wiring more closely. Perhaps that's what's wrong. I bet you're right about the horn button brushes in the steering column being bad, that seems like a pain to repair. It makes sense that they would put a cheapo horn button to simplify the repair. Maybe they blew out the relay when they were fiddling with it. I'll look into getting a new horn relay too.
Thanks,
Erich

 

Erich, The horn runs off the hot wire in the column. Mashing the button, horn ring etc. completes the circuit. It is grounded through the shaft. One place to check is at the rag joint to see if current is getting through that area. My horn was hit and miss, until I made a loop wire around the rag joint. Now it blows loudly every time.

Don't know if this is your problem, but it might be worth a check.



John

 

Hi John,
Thanks for the advice....what is the "Rag Joint"
Thanks again,
Erich

 

Erich, It is that tire like looking material just off the firewall that is between the steering column and gear.

Originally there was a ground that passed through that may be broken, so the recommendation to check it.


John

 

Thanks John, I'll check it out. I really want to get the original horn Button working again. That cheapo button on the column just ruins the in cab asthetics.
Thanks again,
Erich

 

The horn circuit is pretty basic. I'll try to post a quick diagram of how it works. John is right, the steering shaft needs to have a good ground, and sometimes the bearings don't provide that, so running a jumper around the rag joint is a good idea.

Since you have to take the steering wheel off anyway to check the brushes (there are two of them, one under the horn button and one behind the wheel itself), make sure the brush plates and steering wheel nut are clear of rust and corrosion also. Basically, anything metal under the horn button should be cleaned up. I would recommend some dielectric grease inside the cavities that the brushes sit in.

<a href="http://s349.photobucket.com/albums/q400/inxquve/?action=view&current=horncircuit.jpg" target="_blank"><img src="http://i349.photobucket.com/albums/q400/inxquve/horncircuit.jpg" border="0" alt="Horn Circuit"></a>