Another wiring question on my new 1966 F350 Dump-body project. The 3 instrument cluster lights only work when a jumper is in place on the fuse panel, seen in this picture below (note that the jumper isn't completely connected in the picture, it has to contact the fuse/tang to make the lights operate.)







So my first question is, what exactly is this jumper connecting to which allows the lights to operate? It's a brown wire on the back of the fuse panel, as shown in the picture below (kind of hard to see.) I can't quite figure out what the brown wire leads to.




Now the headlight switch does have an extra (8th) lead on it, and the harness plug does not have a wire which connects to this 8th lead. See picture of old headlight switch below, finger pointing to 8th lead which is unused on my harness.




There is, oddly, a wire with a barrel plug (not blade plug like the rest) that is disconnected (see the blue/purple wire I'm holding in the picture below.) This wire is the same color as all of the wires leading to the 3 cluster bulbs that aren't operating, by the way. I made up a little jumper to go from barrel to blade, and connected the open wire to the 8th lead on the headlight switch, but this did not solve the issue or have any noticeable effect.





Any ideas here? I'll update this more later, I have to go to my hockey game now or i'm going to be late!

 

I believe the power to the instrument panel lights are supplied through the headlight switch. In the wiring diagram I have the brown wire supplies power to heater switch. Looking at the diagram -- the blue/red stipe wire enters fuse box from the headlight switch (power side); blue/red exits fuse box (fused/load side) to supply power to three instrument panel bulbs.

 

Seems to me if the instrument lights work using a jumper wire then a fuse should work. Looking at the back of a fuse block the wiring looks identical to the pic in post #12. As Gavin noted, the power source is routed thru the headlight switch and either dimmed, or brighter by turning the headlight switch ****.





Not an authority, wonder if there's poor ground in the instrument lights circuit where the resistance prevents the fuse from completing the circuit? if have not done so, clean the connections on both back and face of the fuse block; also, with the CC (plastic) instrument cluster grounding can sometimes be an issue.

Wiring diag. from 1965 Ford manual:
http://i300.photobucket.com/albums/n...pslm8ut1xf.jpg

 

Here's another version of the '65 diagram, I made this one after spending some time deciphering colors codes on a blurry version I had. There's a few ground symbols I missed, but you get the idea.

 

[QUOTE=Optimusglen;15838947]Here's another version of the '65 diagram, I made this one after spending some time deciphering colors codes on a blurry version I had. There's a few ground symbols I missed, but you get the idea.


Currently In the process of rewiring the instrument cluster in the 65 and was going to replace my wiring manual that is now spindled and mutilated. The pic U posted is certainly an improvement, mind if I ask the source?

 

There was a blurry pic posted in one of the threads here, I used a vector design program to create the colored wiring traces myself.

Currently working on the exterior diagram, but this one is a bit harder to make out the numbers.

 

Yes, believe I posted the link to the blurry wiring diag. out of the Jim Osborn manual, the vector design program certainly clears the image considerably. Thank you for the info., if not too 'hi tech' may look into obtaining the software.

 

It's not too bad, it's a free program that I use a lot to make car illustrations. It's called Inkscape. It's not the most user friendly, but once you learn a few staples it comes pretty easy.



Here's one of my car illustrations, for those interested.



I've been meaning to make one of my new '65 F100 with design/color options but haven't had a lot of free time.

 

Dave, I marked up one of the pictures you took of the fuse box:



I haven't gotten a chance to clean the fuse box contacts or get very far in examining further to confirm/eliminate anything, but I figured I'd update with these points for now..

The jumper was/is routed as shown in green in order to get the 3 cluster lights to illuminate. It seems there is no power traveling through the blue/red wires to feed the cluster bulbs, and this jumper is feeding power through. Another interesting phenomena, the 2 marker lights on the roof of the cab will also only illuminate with this jumper hooked up, AND the marker lights also dim when rotating the headlight switch dimmer ****. The 3 cluster lights DO NOT dim when rotating the dimmer ****, but stay illuminated as long as the jumper is in place.

 

According to your green mark up of pic, you are jumping from an ignition hot spade terminal on the fuse box to the load side of the short instrument panel fuse (these open spade, ignition hot terminals were power sources for accessories such as windshield washer pump). This means you are bypassing the headlight switch, the instrument cluster fuse, and all wiring on the supply side of fuse -- that means any of these can be the problem. You have to back up an isolate each one at a time. Put a volt meter on the supply side of fuse (from HL switch) and see if you have voltage when key is on an headlight switch is on; if you have power then fuse or terminals in fuse box are bad; if you do not have voltage then use voltmeter at power out from HL switch. Keep working backwards until you lose the power.

 

So, everything works when you bypass the headlight switch part of the dash lights right? That tells me that the light circuit is fine. That leaves the fuse, the headlight switch, or the wiring to the headlight switch as the reason for needing to bypass that part of the circuit. The dimmer coils inside the light switch can break, which would give a no light situation for the dash lights. An Ohm reading across the power in to the switch and the power out to the instrument panel lights would tell you if its the switch. Rotate the **** to see if you get any readings. Might just have a bad spot.

 

Hey guys, sorry for the late response. Thank you for all the replies and tips. I just got around to narrowing it down last night. It turned out to be the headlight switch. Funny, because I just replaced the switch due to the original switch's dimmer coil being broken. I guess I didn't expect it since I just replaced it, and it bit me. It was a cheap switch from a local parts store. I'm going to buy a NOS original from millerobsoleteparts.net

Anyway, with the bad switch in hand, there was no continuity between the "battery-in" terminal and the "instrument cluster" tang, except for one reallllly small sweet spot in the throw of the pull ****. I drilled out the rivets and took the new switch apart, and it seems the only time it could make the necessary connection is when a contact inside is actually positioned between two terminal-faces, creating a contact between the two. This is not the correct/intended operation, but I also can't see how this switch could ever have worked the way it's assembled internally. I'll try to get some pictures uploaded of the internals uploaded later tonight and see what you guys think, just for argument's sake.

 

It sounds like a typical child labor built Chinese replacement switch LOL

I love these when doing electrical work, best $20 spent..
Classic Car Wiring . Com : Home of the original color laminated classic car wiring diagram

 

Haha, indeed. Oh well, lesson learned.

 

OP has an F350 with the round speedometer instrument cluster.

CC (Custom Cab) plastic chrome instrument cluster with sweep (horizontal) speedometer only used on 1965/66 F100/250 2WD!