1978 Holiday Rambler - 12V DC problems - no lights

[Kaeferpaul]

I desperately seek an electrical schematic diagram or a service manual for a 1978 Holiday Rambler Presidential 3000. I do have the owner's manual but it’s not very helpful. If not documents, if someone has taken a similar camper apart and has taken pictures of how it was wired, including where the ground points are located that would be helpful too.

We recently purchased this all-original trailer that’s in excellent overall condition. Now I found out why we got it so cheap. I can not get any 12V DC running and tail lights to work. The 110V AC system works just fine when plugged into a power source. I did install new bulb sockets in the taillights. I just peeled back some skin under the tongue and nothing looks funky there. There is a fuse panel behind the tongue but nothing is marked and it’s hard to tell where circuits go. I’ve used a circuit tester and there seems to be power where there shouldn’t be.

I’d like to check and clean up all grounding points but I would prefer not to drill rivets and peel back belly skin on half the trailer just to find them. I thought about fishing fresh wire for all the marker lights but I’m not sure where that would connect. I loved this camper when we bought it but now I’m ready to back it over a cliff. I’m checking all forums with the hopes of getting some good info. Thanks for your help.

[Jon_C]

If nothing 12v is working, good possibility the battery is dead or a bad connection near battery or at battery terminals.

Use voltmeter and start at battery terminals look for 12v there first.

The ground will run from battery negative to frame near battery, just trace the wire, clean the ground connection at frame.

If battery is good keep your meter grounded at battery and probe the connections in second pic for power. At least one of the large red wires should be 12v power coming in then follow it

Also in pic 3 i see large scotch locks, those are bad about corroding and losing connection. When I worked for rv dealer i replaced every one I came across. Pop them open and look for corrosion and test for voltage with meter.

For the tail lights you can use a battery charger, ground negative lead to the frame and probe the 7 way plug with the positive lead, the diagram for the plug is below. When you probe trailer brakes and ground there will be a spark because ground should e a dead short and the brakes should pull 5-7 amps working properly.

The wiring on those trailers is not difficult, you can fix it without a diagram. Jump in there and get started.

[Kaeferpaul]

Thanks for the help. It has 8 wires at the pigtail (the additional one is for the ASCS). It had a 9-pin male plug, which I cut off. The camper is missing batteries so I've been using a 12-volt battery out of my old VW and using jumper wires to test. I have a jumper from the negative post to the green ground wire and use another jumper to power individual wires from the positive post of the battery.

[Argosy]

Have you tested the green wire to chassis to see if it connects?

[Kaeferpaul]

Originally Posted by Argosy

Have you tested the green wire to chassis to see if it connects?

So when I apply the jumper from the negative post of the battery to the green wire my tester shows a ground at taillights but when I apply power then it doesn't trip the breaker in my tester like it should, suggesting an improper ground. Batteries are removed from the camper. I'm only applying power and ground through the pigtail wires to test using an auto battery.

[Jon_C]

I used to work for rv dealer and troubleshot hundreds of trailer wiring.

First confirm your ground from connector to frame is good. Check for continuity with ohm meter from ground connection on trailer plug to the frame. Repair as necessary to near zero ohms.

Then connect your negative lead from battery to either trailer frame or the ground terminal on connector.

Then probe each light circuit on the trailer connector with positive lead. Lights should come on, if not check for burned bulbs, corroded connections at the lights or a bad ground at the light.

The running lights positive wiring are connected daisy chained so 1 bad connection at a light can kill the rest downstream. Look for bad connection on the last light that is lit.

The trailer electric brakes will pull 5-6 amps if all are working properly. You should be able to hear them click when applying power.

Troublshoot one circuit at a time.
If you cant get a light to work, extend your negative lead over to the light and connect it to ground at the light, if it lights up there’s s bad ground at the light. Sometimes the ground is also daisy chained so the bad connection could be at another light.

If everything is corroded just clean all the connections at every light then see what you’ve got.

[Argosy]

What are you using for a meter?

[Jon_C]

I use a fluke 77 but any voltmeter will work. Heres one on Amazon for $10

https://www.amazon.com/Etekcity-Mult...31174576&psc=1

[Kaeferpaul]

Originally Posted by Argosy

What are you using for a meter?

KM10 Vehicle Super Probe - Product - KZYEE

[Argosy]

I think first you need to get a different meter, it sounds like you're getting 2 different results. Just a cheap VOM, most of what you do with these doesn't require accuracy to 2 digits.