Cab light question

[JT_Trucks87]

I have 3 rigs with clearance lights on them. Two of which I have never had any issues with. My79 dually however has two lights dead in the water. Initially I thought it was just bulbs no big deal as all 5 were non op. Well I got 3 of them fixed with just bulbs but the two pictured did not come on with a bulb change. Any ideas? Do these sockets go bad? Are these lights wired in parallel? Any input would be greatly appreciated. I do have another harness that I could use but really don’t want to get into that if I don’t have too.

[ray_mcavoy]

Yes, these lights are wired in parallel. And yes, a bad socket could be a possibility.

However, it's more likely to be a bad ground. I don't know if there were any changes/variations in the wiring harnesses over the years, but on Dad's 77, each cab light has it's own individual ground. And those grounds are via metal clips that simply push onto the edge of the cab roof skin metal that's exposed in each of the light holes. You might find it necessary to remove those ground clips on the non-working lights, clean them up (along with the roof where they clip onto), and push them back into place to establish a good ground.

I've also found that it's sometimes necessary to carefully re-bend the little wire contacts on these wedge base bulbs in order to get them to make a good connection with the contacts inside the sockets. For example, sometimes the bulb will light up when you first start to insert it into the socket, but go out once it's fully seated. Or you can get the bulb to work intermittently by wiggling it around in the socket. Bending the wire contacts out on the bulb a little will often fix these issues.