1977 308 GTB Speedometer help please!

First a little background. When I bought the car the speedo and odo worked fine. Then one day the odo quit working and the speedo was reading low. eventually it stopped working too and would only work after the car had been driven for half hour or so. For some reason the heat from being driven around a while must've made it work. I took the speedo apart and found one of the resistors badly burnt. I couldn't tell exactly what the color bands were on the burnt resistor. It looked like it was orange-orange-black (33 ohms) so I replaced it with a 33 ohm resistor which can be seen in the pic. From that point it hasn't worked at all even when the car is warmed up. I assumed the sender was the reason for the intermittency and replaced it, but still nothing works. Can anyone confirm what the value of this resistoris SUPPOSED to be? It's possible I've just got the wrong one in there I guess. I also want to mention that the SAY115Y looks burnt in the picture, but It's not. it's just got some glue on it from a sticker that was on there. I know it could still be bad, but I really just want to check and make sure I've got the right resistor in there first. Any other ideas would be greatly appreciated too. I've read all the other posts on speedo problems and think the problem MUST be with the speedo now since I've replaced the sender and obviously something caused that resistor to burn up in the first place.
Sean
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Thanks Paul. The one that's in there NOW is definitely 33 ohms because that's what I put in. I mistakenly said 330 ohms in my original post and just now went in and corrected that. Sorry, My mistake. It was so badly burnt I couldn't tell for sure if that's what it was supposed to be so I guessed at the 33 ohms. Any idea what it's SUPPOSED to be?

 

Oops. To answer your question, no I have no idea how to figure out the circuit or what that resistor does. I know just enough to be dangerous with electronics. At least if I know what that resistor is supposed to be, I can get the right one in there and see if it works. If not, I'll probably just send it off for repair.

 

I'm sure it's 33 ohms then. I could definitely see two orange bands on the burned resistor, but just couldn't tell what the multiplier band was. Thanks. I'll check out the link you posted and test it. Hopefully I can get it working soon. Thanks again! Sean

 

I'm wanting to test the speedo with my new sender while not installed in the car to eliminate a wiring problem being the possible cause of all my frustration with this thing. Can anyone tell me how to connect the three wires on the speedo and the two on the sender along with a 12v power supply so I can perhaps just spin the sender with a drill or something and see if this thing works while out of the car? I found a post that told how to bench test the sender, but havent tried it since i just bought it brand new and can't imagine it being bad right out of the box. I just want to hook it all up on my kitchen table and see what happens. At least then If it doesn't work, I've eliminated the car's wiring and I can just send in my speedo for repair and be done with it. Thanks for all the help so far!