What is this part supposed to do? - Electrical.

[keithb7]

Getting into wiring clean up in my ‘38 Plymouth. I decided to pull the original headlight harness. Needless to say it’s in horrendous condition. Crumbling away upon touching it. Lots of bare exposed wire. I’ll build a new harness from scratch. 

 

Wires from the headlight harness went to this 3 terminal box on the left fender well inside engine compartment. 

 

2 wires go to this box. Appear to come from cab area possibly. I’ll dig in further with a multi-meter.  I suspect the two wires come from the hi/low beam foot switch.  The two wires connect to the outer pair of terminals on this box. Then the two head light harness wires connect to the same outer two terminals. The centre terminal on this box was unused. 

 

I’m wondering what the purpose this box is. Its not a relay as far as I can tell. Its not wired up as such.  All it seems to be doing is offering a mechanical connection of the wires. Is it a type fusebox maybe? It’s plenty old for my eyes. I can’t recall seeing one before. Mind you I have not owned a car built before ‘92 since ‘92. 

 

I suspect an earlier owner custom repair. Someone changed out the headlights to sealed beam 6V type. The little auxiliary bulbs in the orignal headlights are gone. The wire is still there in the harness. 

Thanks. 

 

 

 

 

Edited July 9, 2019 by keithb7

[keithb7]

Forgot to mention. I have the original manual. This box I am referencing is not shown in the wiring diagram.  Thx. 

[tom'sB2B]

Is it the headlight terminal? Maybe just mounted farther back in the engine bay?

[dpollo]

that is a relay and was probably used as such for high beam before the sealed beam conversion was done.

[keithb7]

Thanks dpollo. At this point I assume it serves no purpose except join wires together, and hold them close to the fender. I could eliminate it by joining wires directly together. Correct?

[Dodgeb4ya]

Looks like an after market relay... Horn?

[chrysler1941]

Looks like a GM Delco SPST (Single Pole Single Throw) relay. Typically grounded housing with hot connected to middle will connect the outer terminals. Typically horn relay.

[38plymouth]

This is how my low mileage original 1938 plymouth looks in that area. My horn relay isn't on the fender and doesn't look like that.

[RobertKB]

On  my '48 Dodge, '51 Dodge and '54 Plymouth the horn relays looks like the ones below. Your car should have the same, most likely on the firewall. If you can't find it look for the two holes used to secure it with self threading bolts. I have spares if you need one.

 

1948

 

 

1951

 

 

1953 

 

 

 

Edited July 9, 2019 by RobertKB

[keithb7]

Thanks folks. Typically maybe this is a horn relay. It's wired up though as a connection for head lights, not as a relay. Nor used on the horn. Thanks @38plymouth for posting a pic. Mine is not set up the same. Could be because it was built in Canada. Or someone changed things up. I would love to see more photos of your engine bay if you have them. I would like to know how things looked when new. Your low milage car would be good guide for me. Thanks, Keith.

Edited July 9, 2019 by keithb7

[38plymouth]

Here are a couple more quick pictures, apparently my tablet doesn't have a flash so it doesn't come out that great. Let me know if there's anything specific you want to see.

[38plymouth]

Strange, I cant upload anymore photos. Obviously there are a few things that aren't original anymore like the split exhaust, air filter and head bolt covers. 

[keithb7]

I think if you upload 1 pic per post, then post it. Then start another reply and post again, you can upload more pics. Left side of engine and firewall and fender wiring would be great! Thanks. 

[JerseyHarold]

Try having a helper honk the horn while you put your finger on the 'mystery box'.  If you feel it click, you've found its purpose.  Same for headlights/ dimmer  switch.  Your horn may not honk with the ignition key in the off position.

[desoto1939]

It is a headlight relay. To improve the headlights to get brighter and to lessen the amount the electrical voltage has to travel to get to the headlight bulbs.  So when the relay was not used the current ran from the headlight swith to the foot dimmer swith and then out to the junction box on the front fender and then to each individual headlight.  So instead of having the electricity  having to go throught this entire wiring situation the headlight relay was added and the power came directly from the battery to power the relay and then the electricity then went out to the headlights.  If you still have 6v power then keep the headlight relay and since it was converted to sealed beam this will also give you a brighter light. I did this to my 1939 Desoto to get brighter lights.

 

Rich Hartung

Desoto1939@aol.com

cell 484-431-8157