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A friend asked me to help with his 36 120-the right side headlight was not working. Upon opening the headlight bucket found the bulb was not grounded. It appears the whole headlight assembly is not grounded. Is there a separate ground for the headlight bucket? It is attached to the body it should be grounded. When I ran a separatef ground to headlight it worked. Any thoughts would be appreciated.

I cannot say if there was some sort of running change but one 36 A.E.A. diagram labeled as being for a 120B shows the bulbs just grounded thru the buckets themselves. Ground is provided via being attached to the brace and ultimately frame and whatever other body sheet metal it is fastened to or touches.

Another A.E.A. diagram just labeled 36 8 cylinder which might be for a more senior model shows a separate ground wire from each headlight socket brought out to a common point and grounded via a screw point. This is the way it was done on most later models with the ground screw being near or using a headlight terminal junction block mounting screw. I don't see a terminal block on a 36 so it would probably just be going to a convenient sheet metal point somewhere. The parking light bulb on both drawings still shows as only being grounded thru the buckets.

The factory 120 wiring diagram does not show any separate ground wires going to the buckets.

If adding a ground wire solves the problem then you could try to disassemble far enough to clean all the touching and bolting points and see if sheetmetal alone can do the job again. That has not always been successful long term for others so to avoid possible future issues I would discreetly add a dedicated ground wire on both headlight buckets. Many have had to add separate grounds to various parking and tail light bulb sockets on later models due to rust and corrosion affecting the original sheet metal paths and it sounds like you may have the same issue.

My 37 uses a separate ground for both headlights. The likely reason being is the cork gasket that seals the headlight reflector lens to the bezel is an insulator. Yes there are three spring clips that hold the reflector lens to the bezel, but they are a rather poor conductor so a separate ground wire goes from the reflector to the frame. Likely the lower amperage of a 6V system too plays into it, however with the auxiliary ground the lamps light nice and bright.
Bob J.

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Doesn't a 6v system have higher amperage? Otherwise why would it need larger gauge wires over those is a 12v system?

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All conditions being equal, 6v with an equivalent circuit and components typically does require more current. This is demonstrated in Packards case by the breakers they used. On years with a rated headlight circuit breaker, 6v models have a 30 amp breaker and 12v cars have a 20 amp. Until 55 an almost equal number of bulbs are in the circuits protected by that breaker. The 12v junior cars stayed about the same but senior cars have a few more bulbs using the 20 amp breaker.

On the prewar models using headlight switches with the somewhat less sensitive built in "thermostatic overload relay" for circuit protection specs say it must hold at 25 amps but open within 1 minute at 38 amps.

typical. run a dedicated ground neatly and be done with it. want to get fancy...change to a dedicated headlight relay, less voltage loss and less stress on the 80 year old headlight switch.

A 6 volt device will typically require more current (amps) than a 12 volt one, which requires good connections. The lower voltage also demands very good connections at all points. I had problems with a Ford T headlight being intermittent. All the associated parts looked new, but there was still not a good electrical ground between the headlight unit and the fender bracket it bolted to. I cleaned the bolt and nut and the surfaces they contacted clean and bright, and the problem was solved. Any electrical device must have a continuous low resistance path for electricity throughout the entire circuit. Old cars often have some corrosion or dirt or loose fasteners at ground points and in any plugs or other connection points. These will respond to a careful cleaning and tightening. Paint can also be a very effective insulator.