STRANGE Electrical Problem

[InTheDogHouse]

Hello All,

I have a 1986 Ford E350 Class C with a strange intermittent problem where the 12v lights just all of a sudden glow dark orange instead of bright white. Tested the fuse panel and am getting 12.75v there. Tested one of the lights and get 13.5v when switched to one bulb and 2.3v when switched to both.

HOW IN THE WORLD DO I HAVE 13.5v ON ONE BULB? This seems to be an impossibility. Also, WHY on earth would I only get 2.3v when both blubs are on?

BTW, this problem happens intermittently while driving AND when parked. In fact, one night we were just sitting there talking when all of a sudden the lights just went dark orange. STRANGE to say the least. Any help/suggestions would be greatly appreciated!

[InTheDogHouse]

Sorry all, I MUST sound like an idiot. PLEASE DISREGARD PREVIOUS POST.

Upon further inspection, the multimeter wasn't set right. In each interior light I'm getting 5v on one bulb and 2.3v when both switched on. Still, not the 12v that I need for a bright white light. Usually works just fine, I'm sitting there reading and NO MORE. Only the dim orange light. Any ideas?

[RV Wizard]

If your battery voltage is good, then you have a circuit issue. It could be bad connections almost anywhere. I would suggest you access the 12 volt distribution panel and check to be sure all circuits have good clean and tight connections at both the fuse and at the ground bar. Also check to be sure no fuses are loose. Look for signs of discoloring; as this is a sign of overheating. Check to be sure battery cable connections are clean and tight. Also the ground cable to the frame is clean and tight. Good luck and let us know what you find.

[InTheDogHouse]

All new fuses and the ground bars (ac/dc) are tight. Re-stripped all the dc connecting wires underneath the fuses, so have fresh copper wire there. Tested and when the light is switched on I'm getting 12.75v after the fuse into the circuit wire, so it looks like everything from the battery > fuse panel > circuit is good.

Seems like somewhere in the lighting circuit AFTER the fuse panel there's a partial ground (?) that is taking away just some of the voltage but not all - if that's even possible. Still getting only 5v. when light is switched to one bulb. Again, this problem is intermittent and happens at randomly. In fact, it happened one night while I was reading and everyone else was asleep. For no apparent reason, all of a sudden the light just turned dark orange/dim.

Thanks again for any/all help!

[wa8yxm]

Quote:

Originally Posted by InTheDogHouse HOW IN THE WORLD DO I HAVE 13.5v ON ONE BULB? This seems to be an impossibility. Also, WHY on earth would I only get 2.3v when both blubs are on? !

Note: This first part does not likely apply, but it's funny, and true.

I find many RVers have a few screws loose.. No,, not the mental kind, the METAL kind.. and a common hang out for these loose screws is the main breaker box for the 120 volt.. (You might wish to check them.. make sure you are NOT plugged in or running an inverter or generator when you do this)

Now, how this applies.

IN my coach there are not screws in the 12 volt save perhaps a ground or 3.. They use flag/tab connectors.. But a loose/poor/bad connection is a loose/poor/bad connection no matter if it's that kind or the screw down kind.

[John Hilley]

It may be the switch on the light. Try by passing the switch with a test wire.

[RV Wizard]

You have a bad ground in the circuit itself and the other bulb filaments are making a voltage drop potential difference when a heavier load is applied. Suggest you add a good ground to the circuit. You may have to add more than one if the bad connections for ground are in the middle of the circuit. One thing for sure; you can't have too many grounds.

[Roadking]

Like Wizard said, ensure you have a good ground to the circuit, including you have your meter negative lead connected to a known good, solid, ground. Until you know your ground circuit is good use the negative post of the battery as the ground, or negative, side for your voltage readings.

With your lights in question turned on, Using the negative battery post for your meter negative lead connection point then check the voltage at both sides of the light bulb in question. Ideally you should have zero volts on the ground side and 12++ volts on the hot side. If you have more than about 1/10 of a volt on the ground side of the light in question then you have a ground issue.

You can also confirm your battery negative to DC distrution ground circuit by measuring for any voltage between the battery negative post and your ground straps in your DC distribution panel. Do this measurement with your lights and other devices turned on and any voltage indicates a bad (resistive) connection somewhere in the ground circuit.

[bigskymt]

If you have 12vdc at light with no load, 5vdc with one lamp and 2.3vdc with 2 lamps you have a poor connection that is unable to sustain the voltage as you increase the load. If all the lights act the same then go to the lamp closest to the fuse panel and run a dedicated wire (fused) from supply - to light - and look for a change. Next run that wire from supply + to the lamp +. Whatever side corrects the problem is the side with the poor connection.

Or as roadking indicated: DVM from lamp + to known -with and without load.......if voltage drops to 5 and 2.3vdc the + is bad. Next DVM from lamp - to fuse panel +, no load, load, etc.

[InTheDogHouse]

THANK YOU ALL for the advice! After some crawling under the coach chassis, I found several grounds, one of which was LOOSE and rusted. Well, I drillled a new hole in the frame, reattached the ground and SHAZAM, like new again. Victory is SWEET!

[RV Wizard]

Congratulations! You have now passed electrical 101.