Tail light Upgrade

What, you say? My GMC has tail lights! Why do I need to change them?

The original GMC brake lights and tail light assembly has worked just fine for over 20 years. But, automotive safety devices have improved dramatically in the last two decades. A new style lens assembly more than doubles the area that motorists behind you see when you apply the brakes or use your turn signal. It may seem silly to think that a motorhome as big as the GMC might not be noticed by fellow travelers, but it can't hurt to improve the visibility of directional and brake lights.

I purchased GMC update lens assemblies from Sirum's last fall with the intention of making the change right away. To make a long story short, I looked at the GMC rear assemblies on the coach and saw that modifications would be required. One suggestion I received was to remove the entire old assembly and install the new assembly. This would mean that to replace bulbs the cover plates inside the rear of the coach would be removed. Since I'm converting the rear into a permanent bed, this was not a good option. So, the project went on the shelf until I had time to think about some alternatives.

A few weeks ago the guys at Nor-Cal GMC in San Rafael suggested that I cut the backs off the new lenses. Seemed like a good idea to me, so I looked at the rear lens assembly. The aluminum trim used in the original assembly wouldn't come out easily, so I did some other work for a while.

Yesterday (Friday May 14th) Jim Bounds at the Cooperative Motor Works told me that the trim was held in by four tabs bent from the metal lens assembly. Sure enough, the tabs were there - I had missed them earlier because the rear end was in a shadow.

I finished the job on the 17th. The lenses were off the coach for 3 days while I futzed around getting all of the pieces together and thinking about alternatives. Sirum's estimated that the upgrade would take about 90 minutes. Here's what I did:

1.the original rear lens

2. where the new lens assembly goes, once the aluminum trim is removed

3. the newly modified lens, and what it looked like before I took a deep breath and started cutting

4. cutting the back off the new lens - I used a pneumatic cutoff tool. The process took less than 10 minutes per lens. To make all of the cuts I started at the top and cut within 1/4" (more or less) of the weather seal. I clamped the lens in a woodworking vise just tight enough to hold it but not break it. Just cut all the way around the lens. This will leave a piece of plastic holding the back of the lens to the front. The piece separates the brake light from the backup light. Cut across the back and above the separator to release the back. The next cut is vertical through the reflector piece that holds the back piece onto the lower part of the lens assembly.

4. the modified lens assembly has no reflector built in

5. I test fit the modified lens to the rear of the coach. Looks pretty good.

6. Next I'll bend the tabs up and remove the aluminum trim

7. then the new lens is screwed to the back with longer screws. Well, it wasn't quite that easy. First, I used 1.5" machine screws (pan head phillips) for the two inside screws. The two outside screw holes don't match up to the blind nuts in the existing tail light assembly. So, I used a 1/8" long bit and drilled through the metal part of the original lamp holder and then used 2" #8 self threading stainless steel pan head machine screws to fasten the outside of the lens in place. Careful not to over tighten the screws since the lens could break. My lenses don't fit exactly where I'd like, but they look much better and are more visible. When I have a more aesthetically pleasing solution I'll post it.

Overall I spent less than one hour of real working time to do the upgrade - IF you ignore multiple trips to the hardware store to pickup screws etc. Your best plan is to have a selection of screws (machine and self tapping) when you start. With the electric screwdriver on my cordless drill, the lenses came off in less than 5 minutes, the trim came out in about 10 minutes because I wanted to save the trim, positioning and drilling new holes was another 20 minutes. Putting the lenses on for the final fitting was another 5 minutes. Total REAL time: about 40 minutes.