The GMC CCKW

I just finished installing a new wiring harness and everything works great. The problem I am having is in the brake light switch. It would activate if I really put some pressure on the brakes, but while driving, that much pressure would cause me to lock the brakes up.

I bought a new switch and installed it, and that made it a little better but it still won't keep the brake lights on with the amount of pressure that is needed for braking.

Has anyone run across this problem before and are there any hydraulic brake light switches that activate at a lower psi? I've been using Napa #SL134.

I want to avoid putting a mechanical switch in if I don't have to.

Thanks,
Nick

Nick, this is a common problem. There are a number of motor cycle brake light switches that adapt readily to the job, they're operated by a tension spring that pulls on a pin, easy to fit and easy to wire.

There is space on the chassis rail immediately behind the brake pedal to mount the switch and a short flat bar can make up the distance from the pedal clevis pin to the switch spring.

Solved the same problem for me.

Yes this is a problem. That is why many CCKW owners have installed a mechanical BL switch. Also with the small (single) brake light in the back, it gives more warning to those behind you. Remember; safety 1st!

The switch you want is from a 1957 Chev truck. It is a lever action switch and is mounted so that it follows the pedal as it moves. It works quite well. I will admit, it is a pain to install the 1st time.

There are two generic versions: They are both the same except the way the fold in the mounting bracket is bent; R or L

If you are running 12v with a 6v coil and ignition resistor, you can also mount one on the other side engine to follow the starter linkage so that it will short out the resistor when starting. They did this back in the 50's and 60's to give a hotter spark for starting and to compensate for the lower voltage available when the starter is engaged.

Hope this helps

Hey Nick
I use that same switch on all my HMVs with no problems.
Have you checked the "port" with the switch out ,and are you getting a fluid stream ?
I have seen them ( the port )packed with "crud"

Hope this helps
John

Hi John,

When I took the old switch out to put the new one in, I had to hold my finger over the port as a very steady stream of fluid was coming out. I'll check it out, but the port didn't seem to be clogged at all.

On Monday, I'm going to head down the the local truck parts store (Terminal Air Brake Supply, they sell pretty much everything for trucks) to see if they have anything that might activate at a lower psi. If they don't have anything, I might be forced to do the mech BL switch, which I would like to avoid if possible.

I'm at least glad it's not just me having this problem.

Thanks,
Nick

Hey Nick, could I ask you where you got your new wiring harness? Was it Vintage Wiring of Maine? I'm thinking of replacing mine as there is one elctrical problem after another that crop up with the old harness.

I bought mine from Vintage Wiring of Maine. I had them put the red stoplight on both sides, add turn signals, and run the wiring for the add on brake controller. Everything works perfectly (except of course my BL switch, which has nothing to do with them). I've found the best time to call them is in the morning just after they open.

I was having the same problems, one thing after another with my old wiring. I didn't realize how bad the old harness was until I pulled it out to replace it.

--Nick

Hi Nick,

Like everybody else I had the same problem. I solved it by using a Harley- Davidson Motorcycle switch. It is activitated with low pressure and fits in perfectly. Looks original.

See you at Tower Park.

Lee

Hi Lee,

Do you have a part number on the Harley BL switch? I'd like to get this taken care of before I drive up to TP.


Are you going to be putting your truck in the GMC display on Friday? We'd love to have all of the GMC and Chevy trucks that are there in the display and get some good pics.

Thanks,
Nick

Hi Nick,
Thanks for the reply about where you got your wiring harness. I had contacted Vintage Wiring of Maine too. They do great work it's just the costs that's the problem right now. Especially since my accountant just told me Uncle Sam thinks I'm one of those wicked people that work 60+ hours a week and need to pay ever higher taxes to support all those that never work!

Remember:

That you are running 6v which means that you have 2x (compared to 12v) the current with only one stop light in the back. If you run 2 lights or a trailer you are running even more current.

I went the route of the Harley-Davidson motorcycle switch. I had to make an adapter for the wires as the switch uses blade style connectors as opposed to the GM factory bullet style, but that was easy enough.

It works great with very little work and now I don't have to worry about the people behind me not knowing when I'm stopping.

I'll find the part number a little bit later and post it for everyone.

--Nick