1979 f350 custom cab dump truck 351M - restoration project

Battery test for short + to - post test light comes on

Battery (-) ground to truck connected; test light to positive cable and to positive battery post; test light does not come on

Battery (+) post connected to truck systems; Battery negative (-) post off, test light to Battery (-) post and connected to frame of truck; test light does come on - thus do not think a short circuit.

headlights work and turn on and off by switch
Instrument lights work and dim out by rotating to off position
Front parking lights and fender running lights on; but do not turn off
no turn signals
no tail or brake lights
no flashers

Tried already:
replaced headlight switch
replaced turn signal switch
replaced brake switch
replaced high beam switch

Pulled every fuse individually and front lights do not turn off
when disconnect battery they go off
when battery reconnected they stay off
when headlights turned on - they come and do not go off?

 

does it have roof marker lights? if so , do they come on and stay on? they are run off a relay on these trucks...it could be sticking/wired wrong?? just a guess.

 

Thank you for the quick reply:
yes - clearance lights cab and dump body -- at present cab plugs and bulbs are in and just hanging in preparation for painting, one dump body clearance light (rt rear) bottom removed for dump body repairs - just wire (ends taped).


I did notice an instrument wire over the washer and head light is wired to two other wires different in size and I think color codes - this is the only unusual connection I have seen. Also, this all started with a weak light present in rt rear tail-light - I replaced the break pedal switch and that corrected the issue, now I have replaced the turn signal switch, and head light switch and the current problem. Also when the headlight switch is turned off the instrument lights also stay on, and will only dim-out by the turning the dial.


Any thoughts on where the clearance light relay may be located?


In the dash above the steering column is a 3 wire relay I assume is the horn relay, is this correct?


thank you for any help

 

Link to wiring diagrams. 79 appears to be complete. Start there. I would isolate circuits while testing. Unplug harnesses and test one area at a time. Make sure you also clean your grounds as you go. A bad ground can cause some major problems, and weird ones.

1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net

 

Tango Yankee

 

Ford 1979F350 Custom Cab Dump Truck
Request help in identifying photo relay and wire, specifically:
1. “Orange”wire with in-line 30 amp blade fuse, what does it power and connect too?
2. What is the purpose of the relay - ignition, accessory,lights, etc.?
3. What part name or number would I request toreplace the relay?
The “Relay”is located on the passenger side of the engine compartment fender just belowthe voltage regulator and starter solenoid. one relay wire appears to be connected to a post on the solenoid and other end appears to be attached to a post on the driver side fire wall. see PDF attachment

Note inthe attachment photos the 2nd inline blade 25 amp fuse still connected.

The “orangewire was a single connection to the firewall side post of relay, ran to thefirewall along the cowl, and then terminates just above steering column. The end appears to be a clean break, like asheer cut.
Since,the truck has glass tube fuses in the fuse box, it is strange to see bladefuses.
Thetruck at one time had a trailer hitch with under dash brake controller.
The truckhas clearance and marker lights

 

Can anyone identify this firewall relay and what the purpose is and What connects to it.

Top right firewall on cowl above master cylinder, this is a duel post relay - see photo

 

I would say that those are breakers instead of relays. Trailer brakes would have had a fused power. One could be for 12v power to trailer plug also.

 

I like that sticker on the back window. Was that a factory option?