Engine fuse blown

[jayemright]

Hello,

I am the proud owner of an '85 Sunrader with a 22RE auto trans. Recently, my charge light came on, and at the same time the turn signals stopped working as did the gauges. The Mechanic finally found that the fuse labeled "engine" in the cab fuse box was blown. It happened again today, so it looks like there might be an underlying problem causing this. Anybody know what is on that circuit and what could be causing this?

Thanks,

James

[Maineah]

What size is the fuse and do you have a solid state isolator?

[Bodybagger]

Anybody know what is on that circuit and what could be causing this?

Everything in the attached picture runs on that fuse.

If your isolator blows, depending on how it's wired, you will lose charge from your alternator. Coupled with an already weak battery, these systems may pull more current to operate at a lower voltage and blow your fuse.

First, make sure your engine battery is completely charged. This is indicated by an electrolyte specific gravity of 1.25-1.27 and a battery voltage of about 12.6 -12.7 volts.

Start the engine and see if the voltage at the battery climbs to 14 volts ( give or take one volt).

If so, the charging system is working and you likely have a short.

If not, find out why the charging system is not working. Possible cause includes blown isolator.

[jayemright]

Hello,

Thanks to both of you for your replies. The fuse was a 15 amp. The isolator was replaced by the previous owner with a solid state one. Much of this problem started last year after I replaced the converter: THere had been a dead short in the 110 on the fridge, but after I replaced the converter it started working-but it also was putting 110V through the tail lights and that whole circuit. It burnt a lot of grounds, and every friggin' bulb in the tail lights, clearance lights, turn signals, etc. The mechanic I took it to got those working, but now this issue has arisen. I am trying to get all the bugs out of it before heading off to Newfoundland and PEI in a month's time. Again, thanks for your help.

James

[Maineah]

Look at the wiring to your isolator there is a new wire that is attached to the alternator "ign" terminal that goes to the "E" terminal on the isolator it is a smaller wire I would carefully check it and make sure it is not touching any thing it will blow the engine fuse if it has a short to ground. Because this was recently add it would be suspect if you see nothing disconnect the "E" terminal it could be shorted to ground but very unlikely then see if it blows the fuse. With that wire disconnected it will not charge but at least it would either be the problem or eliminate it. Get out your Toyota book if you have it and see what is on that fuse other then the alternator I don't think there is much I think what you saw is pretty much it.

[Gulfstream Greg]

Hello,

Thanks to both of you for your replies. The fuse was a 15 amp. The isolator was replaced by the previous owner with a solid state one. Much of this problem started last year after I replaced the converter: THere had been a dead short in the 110 on the fridge, but after I replaced the converter it started working-but it also was putting 110V through the tail lights and that whole circuit. It burnt a lot of grounds, and every friggin' bulb in the tail lights, clearance lights, turn signals, etc. The mechanic I took it to got those working, but now this issue has arisen. I am trying to get all the bugs out of it before heading off to Newfoundland and PEI in a month's time. Again, thanks for your help.

James

110 volts into the 12 volt side could have smoked alot more than just the bulbs. Sorry to say.

[jayemright]

UPDATE:

It might just be the isolator. Even though it is solid state (replaced about 6 years ago) it could have blown. Here's what's going on: Coach battery appears to be dead. The coach systems works when it is on shore power but die when it is unplugged, Up until the repairs I had done to get the running lights going, the engine and the converter would charge the coach battery, and my 12V system was fine. Then It blew the engine fuse. I didn't have a 15 amp fuse, so I replaced it with a 20 amp fuse so I could get home. Now, with the engine running, while the battery meter says there is power going to the coach battery,it doesn't charge, and I have no liight, pump or anything else 12 V. unless plugged into shore power which as I said, gives me 12 V but doesn't charge the battery. Any advice? Thanks for all of the advice you folks have given me so far.

[Maineah]

The converter/charger should charge the coach battery even if the isolator is toes up. It may take awhile but it should. Can you disconnect the coach battery from the isolator? Does it charge the truck battery with the new fuse installed? If an isolator diode fails it usual fails open so yes it's possible it would not charge the coach battery but your charger still should. Is there a circuit breaker inline to the coach battery? Do you own a volt meter? Sorry about all the questions but every thing is related.

[jayemright]

<br>The converter/charger should charge the coach battery even if the isolator is toes up. It may take awhile but it should. Can you disconnect the coach battery from the isolator? Does it charge the truck battery with the new fuse installed? If an isolator diode fails it usual fails open so yes it's possible it would not charge the coach battery but your charger still should. Is there a circuit breaker inline to the coach battery? Do you own a volt meter? Sorry about all the questions but every thing is related.<br>

<br><br><br>Hello,<br>Thanks so much for your help.  I would be totally lost without you folks.  <br>I have a volt meter, but it had one scale that went to 10V and then the next one went to 250, so an accurate measurement was not to be had.  I borrowed my father in law's and here's what I came up with.<br><br>Engine Off<br>Engine Battery-12.65 Volts<br>Coach Battery10.5 Volts<br>1st lug of Isolator 12.65 Volts (same as Engine Battery)<br>Lug of Isolator going to Alternator 1.05 Volts<br>3rd lug of Isolator 0 volts<br>4th lug of isolator 10.5 Volts (same as coach battery)<br><br>Engine On: <br>Engine Battery-14.5 Volts<br>

Coach Battery14.5 Volts<br>

1st lug of Isolator 14.5 Volts (same as Engine Battery)<br>

Lug of Isolator going to Alternator 15.65 Volts<br>

3rd lug of Isolator 14.5 volts<br>

4th lug of isolator 14.5 Volts (same as coach battery)<br><br>Also-No change in voltage of coach battery when plugged into shore power, but 13.6 volts going out to panel.  No voltage at the panel when just on coach battery-Will it just shut down if it is not up to a minimum level of voltage?<br><br>Could this be as simple as a bad coach battery? It's only two years old, but maybe it didn't like the New Brunswick Winter.   Is the charger from the converter (which I installed last summer) such that it wouldn't be putting a lot of voltage into the coach battery the way the alternator does because it makes no difference in the voltage level at the battery.  The other weird thing is that when there is no power to coach, the water pump light glows like I have switched it on.  Probably just the low voltage playing tricks? <br><br>Replacing the Engine fuse with the 20 A seems to have worked as it is charging although I drove over 100 miles before the last one blew.  It seemed to do it just as I was starting it, as the mechanic told me it did for him.  Some little surge from somewhere. I will look for a circuit breaker  inline to the coach battery is well.  I am 6"5" so looking around in this thing gets a bit interesting at times!!<br><br>Once I get this licked  I am going to re-install the 110.  I am not using any of the existing wiring-That is what started all this (I think it was a short in the 110 part of the fridge)  I am starting right at the circuit breaker and putting in two outlets.  The copper ground on those shouldn't go to the coach ground-Correct?  They are grounded through the shore power. <br><br>Thanks again for all your help.<br>James <br><br>

[Gulfstream Greg]

Looks like the problem is between the isolator and the coach battery. Assuming the power from the isolator goes directly to the coach battery (its supposed to) from the isolator. There might be a automatic reset circuit breaker that did not reset. Look for a small square box with the wires attached, check voltage on both sides of that. Might also be fuse somewhere. You should have voltage on the 1,2 and A pole of the isolator when the engine is off if the coach battery was actually connected to the wire. I think your isolator is fine.

[jayemright]

Looks like the problem is between the isolator and the coach battery. Assuming the power from the isolator goes directly to the coach battery (its supposed to) from the isolator. There might be a automatic reset circuit breaker that did not reset. Look for a small square box with the wires attached, check voltage on both sides of that. Might also be fuse somewhere. You should have voltage on the 1,2 and A pole of the isolator when the engine is off if the coach battery was actually connected to the wire. I think your isolator is fine.

Thanks Greg,

I am going to replace the coach battery as well, and then if I can't find where the circuit breaker or fuse is just run a new line from the isolator to the coach battery. Which lug would that go to?

Thanks,

James

[jayemright]

Yet Another Update: Pulled the battery out, looked at the connections, and followed the leads from isolator lug #2 to the battery. Looked fairly recent, and with no breakers or fuses or anything. Also, while I had it out, I used my car booster battery which was fully charged, and once again, no power to the coach-just that strange little glow from the water pump LED which was switched off..

The battery looked in good shape, and was only 2 yrs old, but was only reading 11 volts. I will get it checked and charged (if possible) tomorrow. It is a car battery anyway, and aren't they supposed to be a deep cycle battery. If the battery's OK, I will re examine the wires running to the isolator from the battery and the converter. The factory schematic shows two fuses in that circuit, but that would have been the original wiring. The other thing I I'ill do is check all the grounds. Does it sound like I'm on the right track? As always your opinions are greatly appreciated.

Thanks

James

[Gulfstream Greg]

The low glow on the water pump LED sounds like you might have lost the grounds some where.

Your previous post said that with the engine off there was no power on one of the isolators main posts (1 or 2). So if the chassis ground is bad there is no return path for that battery and when the engine is running the chassis acts as the return path for the alternator, so you see voltage. Assuming you are using the chassis or body for the negative side of the voltmeter. Hook up a wire to the negative of the coach battery, long enough to run up to the front so that you can take a voltage reading between the batteries negative (long wire) and the isolator post, that will give you some more answers. No voltage, the wire from the isolator to the battery is bad. If you do have voltage then that points to a bad chassis ground. You also need the chassis ground for charging from the alternator to complete the circuit.

The other thing I I'ill do is check all the grounds. Does it sound like I'm on the right track?

Ya!

[jayemright]

The low glow on the water pump LED sounds like you might have lost the grounds some where.

Your previous post said that with the engine off there was no power on one of the isolators main posts (1 or 2). So if the chassis ground is bad there is no return path for that battery and when the engine is running the chassis acts as the return path for the alternator, so you see voltage. Assuming you are using the chassis or body for the negative side of the voltmeter. Hook up a wire to the negative of the coach battery, long enough to run up to the front so that you can take a voltage reading between the batteries negative (long wire) and the isolator post, that will give you some more answers. No voltage, the wire from the isolator to the battery is bad. If you do have voltage then that points to a bad chassis ground. You also need the chassis ground for charging from the alternator to complete the circuit.

Ya!

GETTING CLOSER

First of all, had the battery charged, and it was indeed bad. A casualty of the New Brunswick Winter. I'll take it out and bring it in next winter. Second of all, in searching for loose grounds in the converter area I found a bare copper wire that ran from the bar where the power comes in that has all the green or copper wires going to it. I think the copper wire from the 110 goes to that too. Anyway, I hooked up a temporary battery, and touched this wire to where it looked it was supposed to go: the white terminal going to the converter and bingo-let there be light. So it looks like the converter wasn't properly grounded. I'm just a bit paranoid about hooking it up because the 110V circuit is grounded in the same place on that bar. Where I had the 110 V running through the tail lights before, I am worried I could do this again. Is it OK for the 12 V and the 110V to share grounds? I was under the impression that the 110 would be grounded through the shore power source and sharing copper wires between the 12 and 110 was asking for more trouble. I don't really have a lot of experience with electricity other than wiring my house, and that's pretty simple compared to this. Thanks again for your help, guys.

James

[Maineah]

Nope they all use frame ground that is to keep you from shocked from metal parts on the MH. The Green goes to the round pin on your power cord and to the shore ground. I'm thinking your 120volt problem was a connection between your 120v fridge heater and the 12v fridge heater that's about the only place I can think of where they could tangle.

[jayemright]

Nope they all use frame ground that is to keep you from shocked from metal parts on the MH. The Green goes to the round pin on your power cord and to the shore ground. I'm thinking your 120volt problem was a connection between your 120v fridge heater and the 12v fridge heater that's about the only place I can think of where they could tangle.

That's good news. I'll hook it up, slap a new Deep cycle battery in it and "hallelujah, let there be light!!"

And your explanation of the "fry up" caused by the 110 makes perfect sense-That fridge has only worked consistently on propane, and only intermittently on either 110 or 12 and most of the time it snapped the circuit breaker as fast as you pushed it in. Then it worked for a little while, but was cooking everything in it's path. Guess I won't meddle with the electrical part of the fridge anymore!!

Thanks very much for all of your assistance. I truly appreciate it.

I'll let you know how it all turns out.

All the best,

James

[Gulfstream Greg]

I had an experience one time where a plug in a house (shore power) was wired incorrectly, and the ground was also hot. Found out when I put a sawzall blade against a water pipe. Had some fireworks happening. Just a thought as you did not mention where you were plugged in when you had 120 volts through the tail lights. I am not sure if the shore power ground should be connected with the vehicles ground (negative). Seems like it should not be. AC and DC really don't mix well. The shore power ground is meant for your 120 volt interior outlets. I would have to look at my converter and see if they are indeed connected together.

[Bodybagger]

Check to see if your 120 volt circuit breaker box has the neutral and ground bonded together.

This is typically done by either connecting the grounds and neutrals to the same buss bar or by inserting a green grounding screw through the neutral buss bar into the breaker box.

Isolate the neutral from the ground!

Not sure about the output of your inverter, but on the ones I have seen, the neutral terminal and the battery negative terminal are NEVER at the same potential. There is generally a high AC voltage difference, which could explain the 110 volt taillights.

[Maineah]

By code you can not have a grounded neutral (except in a sub panel). But the ground (ie green wire) and the 12 volt ground are one in the same. The best tool you can buy for your motor home if you are going to plug it in is a simple plug in 3 light tester very cheap and very handy. If it fails the test unplug your shore power right away. Just about every where you go now has GFI’s so it’s less of an issue then it used to be.

[Maineah]

Your panel will have 2 buss bars one is insulated the other is bonded to the panel box. All the white wires go to the insulated buss bar the greens or bear wires go to the one bonded to the panel. In turn there is a usually bear wire (may also be green) that finds it's way to the frame from the buss bar that is bonded to the panel. This ground keeps the truck frame and any metal part from becoming "hot" if some thing goes wrong, it allows it to "ground" through the shore wiring as tires are pretty good insulators. If you connect a "white" or neutral wire to the ground it will work but it will cause ground loop problems and make the safety ground ineffective.