Tried looking on the net, tried looking in the shop manual. No dice, yet! The Olds' use 4 bulbs, that aren't grounded to the dash, that use 2 wires to light. Generator, oil pressure and the 2 temp lights. I cannot find what type of bulb these use and am also trying to find the right socket to put them in. 5/8" hole. I can't believe the shop manual had all the other bulbs, but not this one, listed! Anyone solve this issue? (and if so, is there an LED bulb that will work in these situations?)
My 56 came with no wiring harness, and no sockets at all, for the dash. So, I have nothing to go by.

 

I've got the harness from a 1955. Not sure it would be the same, but if so it would be available for you to use the parts in it that you need.
John

 

On a 55 it is the # 57 bulb, I would think it would be the same on a 56. I have no idea on a LED type bulb, but I bet someone here does... Tedd

 

Ted, I don't doubt you at all, but I can't understand how a 57 bulb would work! From the factory wiring diagram, in the shop manual, it says that 12 v. + is sent to the indicator lights. Then ground is sent from the sender. A 57 bulb has only one wire, so it must take ground from the housing. This is confusing me even more!
2blu442, if it's not too much trouble, I could start with knowing what number bulb is there for the oil pressure light, hi-temp light, cold light, or generator light. If the bulb is still in the socket. If I'm thinking correctly, it should be a 2 wire bulb.

 

I bet it is grounded by the socket. Those are make or break type bulbs, I can't imagine they would need a separate ground, but electrics are not my best thing...Tedd

 

I don't know if this helps you or not, but in one my "retirement boredom" moments, I put together a bunch of spare parts and made a decoration for my garage. See attached. I can't remember where I got the sockets but I'll look later if need be. I know they didn't cost much. #57 bulbs and a 12 volt converter. It all works on 12 volts.

 

Forgot to mention, the sockets are single wire and the socket is grounded to the dash as Tedd said.

 

OK, here's the harness I pulled from under the dash on a 1955 4 door with AC, power windows and power seat. I believe these are the lights in question. There are six metal sockets with one wire going to them and two with plastic sockets and two wires going to them. Yes the bulb is a GE 57 as the others said. Let me know if I can post any other pictures that might help. John

 

Frank - That setup is really neat. I have all the stuff to make one. Thanks for the idea.
Rick

 

1956 saw the first use of a printed circuit board on the back of the speedometer. It is likely very fragile these many years later. Could have some breaks in the circuits that might be causing bulbs to not light. The sockets twist in with the bulb. The sockets on the printed circuit board are not the same as 1955 and older.

Ron

 

No printed circuit board on the back of my instrument cluster!
2blu442...THAT'S the answer! If the socket is a single wire, it MUST have an isolated ground! That's why it's made of plastic and has a separate ground wire (ground goes to the senders)
Thank you so much! I can now search out some new sockets to use. I appreciate the offer to send me old ones, but everything else in the car's electrics are new, I'm always afraid of having electrical shorts. I know several old cars that have burnt to the ground because of them.

 

I recently replaced all the bulbs in my dash and can confirm they are GE#57. In fact, on the back of the panel assembly, you will find some paint marks by each wire. Each paint mark corresponds with the proper wire to the opening for the light as nothing else is labeled. I labeled each one when I pulled the cluster and only discovered the paint marks after I pulled the speedo. I have a '55.

I think the ash tray and glove box bulbs are the same as well.

 

The 1955 Oldsmobile had gauges for generator, oil pressure, and engine temperature while the 1956 used lamps. I couldn't find any reference to bulb types for the warning lights in the 1956 Oldsmobile shop manual. In the 1957 Oldsmobile shop manual it said they were #57 for the warning lamps (see page 330).

 

Done! The warning lights ARE #57, and I found plastic sockets that fit into the dash holes, and have an isolated ground wire. On to the next problem!