No brakes or turn signal lights 73 mach 1

[rjpohl]

Need some help as to where I should start. The brake lights and turn signal worked and I just noticed they weren't. I checked the fuse and it is good, also have 12vdc on both sides of the fuse connections. The 4 way flashers do work so I swapped the flasher and turn signals/brakes still don't work. Are the flashers the same?
thanks
Bob

 

[Cleveland Crush]

Did you replace the emergency/4way flasher above the glove box or just the turn signal flasher?

 

[rjpohl]

Update:
I have switched the 4way flasher (under dash by steering wheel) with the one for turn signals (right side near glove box)
I now have brakes light, the brake light switch only worked now and then. Replaced switch, good bright brake lights both sides. Still don't have any turn signals at all (4 way flasher lights do work). Any suggestions?
thanks
Bob

 

[rjpohl]

both brake lights work if I have turn signal switch off (in middle). If I turn left turn signal on the left brake light doesn't work, if I turn right turn signal on the right brake light doesn't work This happens with ignition switch on or off.
thanks
Bob

 

[vintageman]

Check your connections at the rear harness to the plug connections, I had a similar issue and it just turned out I had to kind of squeeze the harness plug to make a better fit on the lamp plug. Good luck.

Tom

 

[rjpohl]

what do you mean by rear harness?

 

[Steve McMahan]

The flat harness under the rear of the steering wheel.

This one in green:

 

[midlife]

I'm speculating that your turn signal switch needs replacing. 4 way flasher signals over-ride many of the standard turn signal connections within the turn signal.

 

[rjpohl]

I'm pretty sure it is the 4way flasher switch is not working when it's in the off position. I jumped the light blue feed wire and the blinkers started working. I've ordered a new switch from NPD.
thanks
Bob

 

[mrgmhale]

If the flasher replacement does not do the trick it would be good to check the grounds in the trunk, and at the front of the vehicle. When I see goofy behavior it is almost always due to a bad ground. I have attached some schematic snippets to show where the grounds are located, and what the various connectors look like as well as where they are also located. The schematics are from a 73 manual, which is important as in 71 there are several significant differences.

If you ever need to get a full schematic, or engine vacuum hose schematic for 1973, my Go To is Forel publications. For pre-1973 you wont find any useful info re: engine vacuum hose calibration. But in 1973 the Shop Manual Volume 6 has a lot of great emission control and vacuum, hose calibration info. They are missing two 351C 4v vacuum calibrations, which I attached to this post as well as the schematic snippets. I also attached the Mustang Barn vacuum calibrations for 1967 - 1992 (no fee from them or me). Feel free to share the 67-92 vacuum calibratins wherever you like.

In the 1972 electrical schematic you get a decent wiring schematic, although 73 is better. In 71 and earlier the schematics leave a lot to be desired, but better than nothing.

Forel Publications page:
https://www.forelpublishing.com/clickbank/index.html