I'm finally getting around to trying to fix a dimly lit section of the speedometer on my '70 convertible. The nighttime dim spot -- between 55 mph and 95 mph -- has always been there in the 10 years I've owned the car. The one time I had the dash opened up to do other repairs I checked the bulbs behind the speedometer and all were working. It seems I have a wire crossed or something related to the bright lights indicator. As you can see in the first photo with low-beams on, there's a glow in the bright lights field when I'm pretty sure there shouldn't be. It's almost as if the lighting that should be brightening 55-95 mph is in the bright lights field. What should that area look like when the low-beams are on? When I click on the high-beams as seen in the second photo, the dim spot between 55-95 remains but there's a white glow behind the "Bright" indicator. Is that the way it should look? Any help would be greatly appreciated.

 

There are 4 bulbs on each side of the speedo/tach housing. One of the bulbs is not lighting on the speedo side (upper-right bulb on back of speedo housing). Either the bulb is bad or the socket/wire is bad.

The best way to deal with that is to remove the driver's seat first (unless you have a 'personal' midget who can do that work for you). Next, remove the manual override vacuum switch panel via two screws. Remove the vent duct above that (if you have one) via one mounting screw/bracket and by separating the mating ducts to wiggle it free. From that point, its pretty easy to get access to the bulbs. When you are working in there, wear no rings or watch that could cause an electrical short. But you need the power on so that you can "test" for the cause of the problem when you reach the bulbs.

First effort is to leave the bulb/socket in the hole, but twist/wiggle it a bit to see of the light is intermittant. If so, the socket is not making good contact...but you know that it works. Now remove the socket carefully, so as to not drop the bulb out of it and into the speedo head! Remove the bulb and check out the socket. If the sheet metal "clip" is loose or comes out, you can use a couple of dabs of epoxy glue at the spots where the prongs engage with the socket body to hold it in place. Or, if the little contact on the end of the power wire is the problem, you can push it out of the socket and work on that. Just to be safe, I would also change that bulb again...it may have a manufacturing defect or may not be functional from the factory.

I can't think of any other reasons that one bulb would not be working in that housing. Let us know how you fare.

 

Having spent the whole winter replacing bulbs with the complete interior out I have a suggestion.

Since the light is working, it must be not seating properly in the housing.

It may be when you installed it but as it was compressed back into the tight dash it may have slightly dislodged, leaking light into the "bright's" area and dimming it where it should be brighter.

Try playing around with the little metal teeth on the light bulb housing so it more solidly engages on the housing.

The act of returning the driver's side dash pad back in place with all the massaging necessary often causes this.

 

Thanks guys! I'll get in there and get at it. Will post an update. Have a great week!

 

Hi P,
All good advice.
I'll add that it's possible to get the bulb inserted in the socket turned 180 degrees from were it should be. The offset 'tabs' should prevent this, but it's still possible to do. Maybe check that?
Regards,
Alan