1978 Holiday Rambler - 12V DC problems - no lights

So those are circuit breakers. They should be self resetting if they trip but not always.

First check the circuit breakers. Test light negative on the negative post of the battery. Touch the positive probe of the test light to both posts on the circuit breaker one at a time. The light should come on with the same intensity on both posts. That tells you the power is getting through the breaker.

If you have power through the breakers then pick a light that your test light can access while connected to the battery. Maybe try a side marker light. Connect the test light ground to the negative on the battery. Now remove the marker light cover and pull out the bulb. Using the positive probe on your test light touch the two metal contacts in the marker light one at a time. You should get a light on one contact and no light on the other contact.

opnspaces wrote:
You don't need to hook up to the truck, a battery and jumper cables is actually preferred for testing as it eliminates the truck from the equation.

Are the small boxes circuit breakers?


or possibly relays?


I would go with wa8yxm's suggestion of making a really long ground wire. Hook one end of the wire to the negative of the battery. Hook the other end to the negative clip of your test light. Hook the positive of the battery to the trailer wiring. Then go pull bulbs and use the test light to check the sockets for power.

They look like the one on the top.

I've actually done some of that. The problem is the entire belly has an aluminum skin so access to wiring is difficult.

You don't need to hook up to the truck, a battery and jumper cables is actually preferred for testing as it eliminates the truck from the equation.

Are the small boxes circuit breakers?


or possibly relays?


I would go with wa8yxm's suggestion of making a really long ground wire. Hook one end of the wire to the negative of the battery. Hook the other end to the negative clip of your test light. Hook the positive of the battery to the trailer wiring. Then go pull bulbs and use the test light to check the sockets for power.

wa8yxm wrote:
1978 likely has a very poor converter and a dead house battery
The wiring is fairly simple and in fact there are only two "Basic" diagrams

120vac---Converter--Common spot like the fuse block---Isolator relay/device---Cut off switch---battery.


And a 2nd one where the converter/charger is between the fuse block and the rest of the above. All lights and such connect to the fuse block

Now comes the fun part.. IF the fuse panel door says something like Magnetek 6300 that's your problem. Otherwise you need to start power tracing.. To do this I suggest 3 things

one is a "Smart" battery charger (you might also need a dumb one) to make sure the house battery is charged.. You may need a new one (or two)

Now the tools.. a spool of wire. say 18 or 20 ga 25-50 feet. and a pair of "Alligator" clips one on each end of the wire... A good trick is to unroll the wire and find the center.. Rewind both halves at the same time on the spool.

An anautomotive test light. This looks like an old fashion ice pick plastic handle is clear or translucent.. Bulb inside and a wire with a clip comes out of the handle.

Start at the battery. Clip to negative tip to positive bright light = good if not re-seat the bulb and try again. (NOTE battery must be charged)

Now transfer the clip to any unpainted metal part (Frame) still bright GOOD not bright you have a problem on the ground lead.

Now move out... Along the positive wires.. Find where they go still bright at the other end of the wire.. Good Still bright at the other end of whatever that wire is hooked to.. Good. Problem exists between bright and dark

What about that spool of wire? Have problem finding a good ground point.. Use the spool and hook one clip to the test light clip. the other to the battery negative.

This is my most useful 12 volt diagnostic tool

Checking an entire 30 fuse panel (modern blade fuses)

Find a good ground or use the extension
Touch each end of the fuse (The little windows in the fuse)

Bright bright = good
Dark dark = Switched circuit no test
Dark bright or Bright dark = Blown.

You don't even need to pull the fuse to test it

(Works with the 3AG style cartridge fuses too)

Thanks. It has an old fuse panel just behind the tongue. The fuses look more like small relays. There are no little windows like in blade fuses or even glass fuses. I do have a test light and a fancy circuit tester.

opnspaces wrote:
Hate to say it but there's not going to be any manual for that trailer.

Know that there are two 12 volt systems on the trailer. The taillights/marker lights are one 12v. And the interior (water pump, lights, furnace, vent fans etc) are the second 12 volt system. The interior lights water pump, fans and such are still 12 volt even when plugged in to shore power.

Are both 12v systems bad or just the taillights/marker lights.

If only the taillights/marker lights are you testing with the trailer plugged into the tow vehicle? Or are you using the onboard battery and some test leads?

I'll say you're probably on the right path looking for ground problems. Try looking on the tongue. Follow the negative battery cable from the battery post to the frame. Pull that attachment bolt and clean up the ground point so it has bright shiny metal.

Follow the positive cable from the battery to the trailer. Somewhere along the line you'll probably find a 12v circuit breaker. is it in good shape or all rusty? If rusty pull it off and take it to the auto parts store and get a new one with the same rating. If the rating label is all worn off I would probably start with a 25-amp one.

If you are testing when plugged into the tow vehicle; Get a set of jump-starting battery cables. Make a good ground connection from a bare spot on the trailer to a bare spot on the tow vehicle.

The 110v AC and 12v stuff coming off the converter are all working. It's only the 12v exterior lights not working. I cut off the plug as it had a 9-pin adapter which doesn't fit the 7-blade outlet on my truck. The trailer came without any batteries. I didn't think that would affect the lights though. I have been testing using a car battery and jumpers. Do I need to hook up my truck?

1978 likely has a very poor converter and a dead house battery
The wiring is fairly simple and in fact there are only two "Basic" diagrams

120vac---Converter--Common spot like the fuse block---Isolator relay/device---Cut off switch---battery.


And a 2nd one where the converter/charger is between the fuse block and the rest of the above. All lights and such connect to the fuse block

Now comes the fun part.. IF the fuse panel door says something like Magnetek 6300 that's your problem. Otherwise you need to start power tracing.. To do this I suggest 3 things

one is a "Smart" battery charger (you might also need a dumb one) to make sure the house battery is charged.. You may need a new one (or two)

Now the tools.. a spool of wire. say 18 or 20 ga 25-50 feet. and a pair of "Alligator" clips one on each end of the wire... A good trick is to unroll the wire and find the center.. Rewind both halves at the same time on the spool.

An anautomotive test light. This looks like an old fashion ice pick plastic handle is clear or translucent.. Bulb inside and a wire with a clip comes out of the handle.

Start at the battery. Clip to negative tip to positive bright light = good if not re-seat the bulb and try again. (NOTE battery must be charged)

Now transfer the clip to any unpainted metal part (Frame) still bright GOOD not bright you have a problem on the ground lead.

Now move out... Along the positive wires.. Find where they go still bright at the other end of the wire.. Good Still bright at the other end of whatever that wire is hooked to.. Good. Problem exists between bright and dark

What about that spool of wire? Have problem finding a good ground point.. Use the spool and hook one clip to the test light clip. the other to the battery negative.

This is my most useful 12 volt diagnostic tool

Checking an entire 30 fuse panel (modern blade fuses)

Find a good ground or use the extension
Touch each end of the fuse (The little windows in the fuse)

Bright bright = good
Dark dark = Switched circuit no test
Dark bright or Bright dark = Blown.

You don't even need to pull the fuse to test it

(Works with the 3AG style cartridge fuses too)

The chances of finding such documentation, for a 45 year old defunct brand RV(even if they ever existed, which I doubt), are slim to none.
You might find a RV restorer that might have some factory records.

Hate to say it but there's not going to be any manual for that trailer.

Know that there are two 12 volt systems on the trailer. The taillights/marker lights are one 12v. And the interior (water pump, lights, furnace, vent fans etc) are the second 12 volt system. The interior lights water pump, fans and such are still 12 volt even when plugged in to shore power.

Are both 12v systems bad or just the taillights/marker lights.

If only the taillights/marker lights are you testing with the trailer plugged into the tow vehicle? Or are you using the onboard battery and some test leads?

I'll say you're probably on the right path looking for ground problems. Try looking on the tongue. Follow the negative battery cable from the battery post to the frame. Pull that attachment bolt and clean up the ground point so it has bright shiny metal.

Follow the positive cable from the battery to the trailer. Somewhere along the line you'll probably find a 12v circuit breaker. is it in good shape or all rusty? If rusty pull it off and take it to the auto parts store and get a new one with the same rating. If the rating label is all worn off I would probably start with a 25 amp one.

If you are testing when plugged in to the tow vehicle; Get a set of jump starting battery cables. Make a good ground connection from a bare spot on teh trailer to a bare spot on the tow vehicle.