As some of you know my new 1970 F-350 was giving me some electrical wiring problems. There were some wires that were chewed off by little critters. The PO instead of connecting those wires, rewired the brake/tail/turn and the bed marker lights.

First my marker lights did not work when it rained, then they came on when I applied the brakes, then they stopped working altogether. I was under the truck looking for a loose wire, and then I noticed my turn signals did not work when the lights were on. Then the turn signals did not work at all. Then the brake lights did not work.... So I lost every thing back of the cab, including the back up lights.

Messing with it today: Could find no loose wires. Then I noticed where the PO had grounded several wires. He had about 3 wires from taillights grounded at a stake pocket. I took it off got sandpaper and steel wool and got the rust off and .... all marker, and taillights work!


But the brake and TS do not work! Any advice as to where to look? Also, are there fuses under the dash on the passenger side or is there just a relay. The fuses on the driver side all look good, besides I don;t think any of them are for brakes or TS. I think I used to hear a click on the passenger side when I applied the brake. what was this? I don't hear the click anymore.

Any ideas?

 

Well, brake lights and turn signals work through the turn signal switch. If the switch is screwed up then you won't have either.

Check under dash for the big flat plug coming from inside column. Make sure everything is hooked up. Or do the front turnsignals work???

I would take the bed lights and ground them to the frame somewhere. That way a rusty rivet won't make them fail.

 

The front parking lights work but the front TS do not. I also replaced the flasher with 2 others I have and no change...

 

I had a problem with the front signals only not working even after replacing the bulbs. It turned out the sockets were wore out and not making a good contact and i redone the ground wire at that location on each one. Mine was on a 79 , which have cheap plastic sockets, yours may have metal so you might just need to clean them . My $0.02 worth, good luck.___

 

Well, I would get a volt meter and test the sockets. Confirm IF the front is even getting power to turn signals. If no power, then I'd say your turn signal switch is bad, or wiring is bad/wrong/etc at the column.

The wiring to the front and rear are at different points, so I don't think it is downstream. The TS switch is my first thought. The flasher relays are likely not the issue, as they just cut the juice to flash the bulb. They have to get power first.

That is where I would start.

 

1967/72, 1973 and 1974's before serial number T80,001 have metal parklamp bodies, the sockets (includes the wiring) are swagged into them. The separate lenses attach with philips head screws.

1974 from serial number T80,001, 1975/77 and 1978/79 parklamps are a one piece molded plastic assembly. The plastic sockets twist into them.

Which would you rather have, swagged in sockets with the wiring attached that can be a real b!tch to replace, or plastic sockets that are the same as 1971/80 Pinto, 1975/91 Econoline that are EZ to find and install?

 

Update: after messing with the truck today... I took out the fuses to check them, cleaned them up with sandpaper, put them back in, no change...

Later this evening, I had to move the truck so I tried the turn signals before I started the truck. Turned the key to the left to Aux to try the TS. They did not work. I sat there in thought with the key and TS still on and after a few seconds they started working!!

But, still no brake lights! Here is my thinking: it rained the last 2 nights. Yesterday was cloudy all day. Today it was warm and sunny. Did some moisture get into a junction and now only dried out, thus allowing a free flow of electricity? The PO did some funky wiring: in some spots he used an heavy duty orange extension cord; other places he used household wiring. He joined wires together with wire nuts!! Is moisture my problem?

 

Usually not. I'm guessing it's a contact issue with one of the "junctions" the PO made.

 

Make sure you are replacing the turn signal flasher and not the 4 way flasher, common mistake. Then start right where the wires come out of the steering column and with a test light see if you have function there. If not, it's the turn signal switch. If it's good, move on down the line until you find th bad place.
Good grounds are essential, lots of them, engine to frame and cab, frame to bed ect. Any bad ground causes the flow to find it's own ground, often through a different light.

Also, if you don't have a good test light, go get one. You can't do even the simplest electrical diagnosis without one.