03 Pete 379 6 NZ 18 speed , Jake Brake issue

Bought my truck 3 1/2 years ago. First year Jake brakes constantly cut out on brake stages when using Jake , so I just didn't use it much. Had over head done had it fixed or adjusted. Worked for 2 weeks. Started again.
Last year did ole school overhaul , had jakes fixed again. Wiring harness end was loose. Mechanic fixed it. It last a year. Now it's doing it again.
I was told there was 1 Jake wiring harness. Someone said there were two.
New one are $300.00 at peterbilt.
How many do I need. ? 1 or 2.
I'm tired of not having jakes working ,
Was told after a while the harness wears out due to heat. Which I can see that.
But if it was fixed and lasted a year after it failed couple other times. Then aparentaly the latar of the mechanics knew what he was doing.
So to save myself some money.
Can you just buy the ends and replace them if that can even be done.

Thanks in advance.

 

Great. Thanks so much.
Now question.
Is it something I can do myself. Without special tools. I pretty mechanical on my truck at doing a lot of minor stuff . If I take off valve covers. Is it right there. And do I need to torque the cave covers back on. ?

 

Had my overhead done. Whatched him do it , and now I have a ticking sound coming from engine I've never heard before. I know he done it right as I done my research on it before he did it , as Truck runs good now and the jakes were out of adjustment , after over head. Jakes are working great. Just that ticking sound I hear now.
I made a video of it. But it won't let me post on here

 

It's while the truck is running. I can't hear it if jakes are on cause I got straight pipes.