Cabin lights dimming with 4ways

[76chinook]

Hi
My first chat.
So excited to see there is a group of Chinook fans!!
We live in British Columbia,Canada, and have only seen 2 Chinooks simular to ours while on the road.

We have owned our 1976 Chinook M18 Plus since 2003. We bought it from the original owner. Orginal owner and myself have looked after it well, and love it! Odometer reads 97,000 miles, so guessing it has 197,000 on it. Everything is original, and still works!
We just went winter camping last weekend in Whistler, and the furnace worked fantastic, but we were hooked up to shore power.

The electrical problem we have been having latley is strange. While camping at the end of last August, we noticed that one of the rear brake lights would come on slightly while the water pump is turned on. Also noticed that while the 4 way flashers are on, the cabin lights would dim and brighten slightly.
I have a high end 2'x4' solar panel installed on the roof, display module, and two 6 volt deep cycle batteries in series (All test fine). So far this system has never failed, and we have endless power for everything in the backwoods.
I figured a ground problem, so I checked, cleaned, coated connections with Grote Ultra-Seal (non-conductive cream for electrical),and confirmed continuity on all grounds. Took apart the rear brake lights, cleaned them up.
Cabin lights still go dim and bright to the rythm of the 4 ways though?

I have the original manual for the truck, and wish I had a wiring diagram for the cabin.
I know when the truck is running, it charges the cabin batteries also. I know when we are using the cabin batteries during camping (truck not running), no power from the truck battery is consumed by our cabin power use. There must be a one way device that allows this all to happen.
Is it the solenoid on the firewall?
Would a faulty solenoid cause my issues? If so, is there a way to test the solenoid to confirm it should be replaced?

Thank you.
Stuart

[caconcourse]

Hi Stuart,

Welcome! That is a really old Chinook, compared to most of us on the forum, so it may be hard to get specific information but I can provide some general troubleshooting suggestions.

I would focus on that rear brake light wiring. If it comes on when the water pump is turned on, there must be a partial short somewhere, giving it power from somewhere (less than 12V if it is dim, indicating a weak connection). The brake lights are also involved in the 4-way flasher, so a short could produce a parasite draw on the cabin lights in the opposite direction.

While the pump is turned on and the brake light glowing, you can disconnect the chassis battery to see if the power is coming from the cab battery or the coach batteries. Similarly, if you disconnect the coach battery, you can see if the stray power source is the coach batteries. (if it goes away when you disconnect the cab battery, the stray power is from the coach, and vice versa.) if it comes on with either battery connected, then there is a connection between the two systems and the solenoid is at least connected, but may or may not be malfunctioning.

It seems like the water pump circuit is also involved in the short. Could be some worn insulation in a wire harness, or even moisture from a water pump leak that allows a partial short in that rear brake light wire circuit.

[chin_k]

There is a solenoid in the driver side of the rig under the hood, but that is for my 2000, and I have never see a 76 under the hood. I vaguely remember for the older Chinook, both the coach and chassis batteries are under the hood.

Anyway, there is some short between the chassis' light system and the coach electrical system. You need to confirm that, and in order to start, you need to find the solenoid that connect the two system together, and take it out of the equation. I would follow Clay's suggestion above to start. I would also take a quick look at the trailer light assembly near the tow hitch, if you have one.

Out of curiosity, does the interior light get brighter when the flashers turn on? I assume the opposite is true, since I can't think of a way to short the two circuit to make that happens. However, if all of your batteries are in good shape, you should not notice the dimming effect when the flasher is on. I am really interested in not only what happened, but how it was shorted to result in the effect that you observed, which I found to be difficult to explain with a simple short circuit.

[76chinook]

Thank you so much for the input!!

I will look into your suggestions, and report back my findings soon.
I am 57, still work, freezing here, and only work outside when I have to.

So great to know there is such a huge following for Chinooks.!

Anyone know how to get the cabin electrical drawings for my Chinook?
Cheers!
Stu

[Blue~Go]

Welcome, 76!

The 18+ are so clean and simple and classic - and are the inspiration for our later rigs. Good on you for keeping it up so well.

I'm going to guess you have some simple solenoids under the hood at most. Reason I say that is that I helped kyidletime (another member here) figure out his '95, and even that didn't have something like the Surepower separator of later rigs (which is now also outdated, but it's "newer outdated" ). His had just two solenoids. IF I remember correctly (it's been a few years now), one connected anytime the ignition was on (to charge the coach batteries from the alternator/start battery) and the other one..... erm.... maybe that was for self jump start? I forget.

Newer ones are relays that open and close depending on voltage, but just charging whenever the ignition is on works too.

On the light flashing.... it does sound like something a ground would do (it's always a ground, right? ). Mysterious tho.

[chin_k]

Blue, I think in 76er's case, it is the red/positive, not ground.

[Blue~Go]

You are the ace trouble-shooter with electrical. I'd bet on your idea completely over mine. Seriously.

I think it's trailers where it is "always a ground."