Rewiring headlights with relays

[Gordon Webster]

I rewired my headlights using Roy Mueller's 2 part Youtube video as a guide. They work great but new issue. Where I was getting an indication of about 13.2v on my dash gauge before I now am getting only 12v.
I still get the drop of about 2 volts when I turn the lights on but they are much brighter. Anybody know why? Did I do something wrong or is it normal on these coaches?

[Edward Buker]

Gordon,

Because the old headlight wiring path had added resistance due to the total wire length and wire gauge there would have been less amps total being drawn by the light circuit then there is now. When the wire length is shortened, by using the relay path, the lights now have more available voltage with less total resistance in the path and therefor can pull more amps from the long wiring path back to the batteries. That probably explains the increase in voltage drop as seen at the dash gauge with the relays added. As long as the dash gauge reads as it did before with the headlights off you should be fine. That should still be the 13.2V. The dash fan will also create a drop at the dash voltage gauge.

Later Ed

[Gordon Webster]

Sorry I wasn't clear. The dash gauge no longer reads the same. It read 13.2 before with engine running with no extra load but now reads 12.0. that's what I don't understand. I need to check and make sure it is still delivering 13.2 to the chassis batteries but have no idea why it dropped at the gauge.

[Edward Buker]

Gordon,

If the battery voltage is fine, I would not worry about the 12V at the dash gauge, as Gerald says these are for entertainment purposes and accuracy is not high on the list of attributes. I can assure you that this wiring change cannot explain the voltage drop with the headlights off.

You could measure the larger leads across the large solenoid at the bottom of the copper buss and see if there is voltage drop there. It should be near zero or a tenth or two of a volt. If it is more that you could have worn, corroded or burned contacts. It is a wearout item that tends to fail in time. Basically this turns on the ignition buss (the one on the right) and it should be very close in voltage to the left buss if all is well. Possibly an explanation here. Having the dash air on could play a role voltage wise here having fired up the condenser fans and dash fans as a load also.

Later Ed

[Gordon Webster]

Checking to see what else might be on was a good point so I made sure nothing else was running. I still get
only about 12v on gauge and it drops to about 8.5 v when I turn on running lights, headlights, and air conditioning. Obviously not right but I don't know what to check. I know the headlights are wired right with the relays. I've triple checked that.
Maybe the person was right about the gauge being only for entertainment.  Seems a shoddy way to wire a coach. Hope someone, maybe Roy Mueller, will tell me how to fix it.

[Edward Buker]

Gordon,

Have you checked the battery voltage or the solenoid voltage measurement that I described in my last post on this? That info helps with the trouble shooting. The solenoid is the silver can at the bottom of the two copper buss bars in the electrical bay under the drivers seat.  Hard to tell you how to fix something without some measurement information on your coach.

Later Ed

[Edward Buker]

Gordon,

One more thing, if you check the voltage across the large solenoid, do it with the large dash load like you had before when you noted the 8.5V reading. You will be measuring across the two large lugs using the two probes on a DC voltage scale.

Later Ed

[Gordon Webster]

I followed the advice and checked voltage in the wiring bay (front driver's side) and it is battery voltage at every point. Doesn't change at all when I run the engine and get 13.9v at the chassis batteries. At every point in the wiring bay it stays at battery power. I have no idea if that is correct but it means the lights are running directly off the battery and never getting full alternator voltage-thus the weak headlights, even after they are relayed.
Someone has messed up the wiring in this coach or it was done very poorly at the factory.
Please check yours and let me know if you can get full alternator voltage anywhere in that bay.

[Steve Huber Co-Admin]

Gordon,
If you've got 13.9 v at both the battery and ignition buss bars and the headlight mod is installed, the voltage drop is occurring has to be between the ignition buss and the headlights. With the mod installed, the headlight voltage comes from the ignition buss bar, through the headlight CB (probably #25) and then to high and low beam relays (pin 30) you added as part of the mod. The output of those relays (pin 87) should go directly to the headlights. If voltage is low for both high and low beam, it would indicate a resistive contact in the headlight relay (CB25). If that's not it, I would suspect a faulty ground at the headlights as the  high and low beam voltage paths are separate between the new relays and the headlights.
Good luck,
Steve

[Edward Buker]

Gordon,

This started out that you had bright headlights with Roy's relay mod which is everyone else's experience also. Understand that when the headlights are wired better through relays that they will draw more current and that may change the dash voltage gauge a bit causing it to be lower with the headlights on. That is not a problem. The fact that the battery voltage with the engine running is 13.9 at the battery and I think your note indicates that you also measured the 13.9V in the bay. That would indicate that all is well and there is no significant voltage drop between the battery and the electrical bay. Everything that you measured, both battery and bay is seeing the alternator voltage otherwise it would be 12.6V or less. The alternator goes through an isolator to the battery and from the battery to the electrical bay. 13.9V is a good value for the alternator output so that is also fine.


Later Ed

[Steve Huber Co-Admin]

Gordon,
I think I misread your previous post. Sorry.
If I understand correctly, with the engine OFF you measure approximately 12v at the chassis batteries and at the battery buss bar in the electrical bay. When the engine is running you measure 13.9V at the chassis battery terminals but  still read 12v at the battery buss bar. Is that correct?
If so, not sure how that is happening as the battery terminals and the battery buss bar are electrically the same point except for some junctions in the voltage / ground path. If there was a resistive connection, the buss bar voltage would still vary between engine on and engine off. Even with a mis-wire I don't see how the electrical bay never varies from 12V as there is no constant 12v source with the engine / alternator running. Missing something.
Steve

[Gordon Webster]

Steve, your first paragraph is correct. With engine off or engine running the voltage in the wiring bay remains exactly the same. I have put my volt meter leads on every post and it is all the same. I certainly expected at least the large red wire coming to the silver relay that looks like a starter relay to change to alternator voltage but it doesn't. I'm wondering if others can check and see if theirs is the same. I don't know if this is normal from the factory or someone at some point has done something to change my coach.
And alternator voltage would certainly brighten my lights.
And I have no clue why it shows battery voltage now on the voltage gauge instead of alternator voltage it showed before I relayed the lights. It still drops

[Gordon Webster]

The message I just posted lost the last few words somehow.
I was saying the voltage gauge still drops with every item turned on. All the way down to about 8.0 volts with headlights, driving lights, and air conditioning on.

[Steve Huber Co-Admin]

Gordon,
The alternator output goes through the isolator before being applied to the batteries. The isolator is there to ensure that if one set of batteries are discharged, they don't discharge the other set.
I'm wondering if there is a problem with the isolator and /or its associated wiring. If you are getting alternator output at the chassis batteries, what are you seeing at the house batteries?
First though, there are 2 large fuses (~200amp) in the battery compartment to protect the chassis and house batteries. Check the voltage on each side of those. The output of the chassis fuse should be the same as you are seeing at the large solenoid in the elec bay.
Steve

[Edward Buker]

Gordon,

With the coach not plugged into shore power, generator off, engine off, can you measure the DC voltage at the house battery bank, chassis battery bank, then the large red wire in the electrical bay to the ground buss with the headlights both on and then off. Then start the engine and record all of the same measurements again. Then post all of the numbers that you measured to this thread in a reply.

We need the data regarding the measured voltage values in order to help you sort this out.

Later Ed