slight shock

There definitely is an electrical problem. A loose or missing ground could definitely could be the issue. That could be a dangerous situation, it needs to be checked by a professional. Potentially you have 220 volts going to the fifth wheel, which would definitely put a big hurt on someone!

Was he plugged into shore power when he received the shock?

If yes he has a hot skin condition which is dangerous , potentially fatal.

If not plugged in was it a standard static shock?

he was plugged into a 15 amp outlet from his garage..ai told him to check his electric cord reel... have heard of those grounds failing

Put a 3-prong outlet tester into that power source.

https://www.homedepot.com/p/Power-Gear-3-Wire-Receptacle-Tester-50542/206212329

Aka the breeze wrote:
he was plugged into a 15 amp outlet from his garage..ai told him to check his electric cord reel... have heard of those grounds failing

Likely has 2 problems.
First is a missing ground connection, as you stated might be on the house side of the wiring so needs to check the entire "pathway".

Second is the source of the voltage he felt on the lug nuts. If he has a 120 and/or 240 electric water heater I'd check that place first.

I thought this was a 12v system off battery power for brake action. Still yet, a ground problem.

Aka the breeze wrote:
My neighbor just purchased a new ( used ) fifth wheel..

When he was inspecting it at home, he received a slight "shock" when touching the lug nuts... He did not feel it anywhere else..

I am thinking maybe a loose ground wire? what says the experts here??

Glad he was only plugged into a 15 amp circuit! This is a very dangerous situation. If plugged into a 30 amp service, could potentially deliver a 220 volt shock to someone! Could be a problem at the pedestal side, or in the trailer! Again, it needs to be throughly checked by a professional before someone is seriously hurt or killed!

Coach-man wrote:

Aka the breeze wrote:
My neighbor just purchased a new ( used ) fifth wheel..

When he was inspecting it at home, he received a slight "shock" when touching the lug nuts... He did not feel it anywhere else..

I am thinking maybe a loose ground wire? what says the experts here??

Glad he was only plugged into a 15 amp circuit! This is a very dangerous situation. If plugged into a 30 amp service, could potentially deliver a 220 volt shock to someone! Could be a problem at the pedestal side, or in the trailer! Again, it needs to be throughly checked by a professional before someone is seriously hurt or killed!

Absolutely not. RV 30A service is 120V only. No 240 in any form.

** UPDATE **

We found the issue.. The extension cord he was using as a temp was heavy duty with 6 ga wire, BUT..... ( or someone ) cut the ground prong off the male end... SO it was plugged into the wall socket, without the ground.....

He didn't think that was an issue, I removed the cord, CUT both ends off it and trashed it. We then plugged another into the wall.. All is good now.

Thanks all

Good that you found the issue before someone was hurt! Unfortunately way too many people do not realize how important proper grounding is.