Headlight override circuit, Rev A

[cranetruck]

Here is a way to add an override switch for the headlights on the deuce.
With the relay in the ciircuit, operation will be normal when using the 3-lever light switch. If/when the light switch circuit breaker (CB) trips, the relay contact will open, but can now be overridden by manually switching the headlights using the "override switch".
The relay reduces the load on the light switch circuit breaker (removes the headlight load curent) so that it may not trip at all, but if it does, the manual override switch may be used for headlights. With a tripped CB, there won't be any tail lights either and a similar circuit arrangement would have to be used for each light function to retain the intended operation of the 3-lever light switch.

The diode across the relay coil removes the inductive kick and protects the switch contacts within the 3-lever light switch. In the same fashion, another diode may be installed to protct the relay contact, but the load is basically resistive so it shouldn't be necessary.

Robert, thanks for the relay offer! I have an "aircraft" type relay, which I have saved for this job and won't need another, but thanks anyway.

 

[Recovry4x4]

Neat! It's not everyday that someone has a common sense approach to electrical engineering. When I was younger and heavily into the 4x4 stuff my trucks were always weighted down with the big brother of the relay, the constant duty solenoid. Everything of importance on the truck was wired in 8 or 10ga and had solenoids all over the place making connections. Great concept Bjorn with the override. All this makes me wonder about the pipeline truck. In service drive it has all the standard deuce lights plus 12 marker lights. Even operating in blackout the truck has 6 blackout marker lights. I don't think the circuit breakers and the 3 lever switch was designed for that. I guess we'll see when I get it done.

 

[cranetruck]

The built-in CB in the 3-lever light switch has a rating of 20 amps. A dozen marker lights totaling 50-60 watts shouldn't be a problem, at least not once turned on. It's the cold filament inrush current that is a problem, as you know, it can be up to 10 times the steady state current.
This is what blows the (late model) turn signal flashers. One solution is to run a small current to the lamps at all times to keep the filaments warm.

 

[Recovry4x4]

I'm not sure what denotes a cold filament. I'm sure the filaments in my lights never get below 85 here.

 

[cranetruck]

That's very funny! :hop:

 

[Recovry4x4]

Sorry couldn't resist! The hot season is here and I'm iritable. Sure miss that Aberdeen weather.

 

[n3uka]

Don't miss it too much. It is 90's and humid here now.

 

[Recovry4x4]

Yeah, I figured it was getting hot. Dave, did you get my response to your email?

 

[cranetruck]

Installed override circuit last week. Works as expected. Used a 25 amp mil-spec relay. Pictures when possible.

 

[cranetruck]

A 25 amp mil-spec relay can handle up to 75-80 amps of inrush current or an actual lamp load of 8-10 amps according to the spec I found. That's close to 300 watts of light output.