MaineErik Posted March 18, 2017 Share Posted March 18, 2017 Hi Folks - Since buying the MH the coach battery has never charged from the alternator. I suspect the isolator and/or relay(?) or other electrical hardware is to blame. (Coach charges fine when plugged into 120AC). So today I decided that before replacing stuff (not even sure what to replace it with) I would try to clean up the corrosion on all the terminals to see if that got it working. Here is a photo of what it all looked like before I got started: Well the first thing that happened was that the relay (2 post thing on left) broke while removing the nuts. This is what it looks like up close: I have searched online but cannot confirm exactly what this is (though I suspect it's a relay) and absolutely have not been able to find one like it (or any 12v40a relay with just two posts). Am I even on the right track with cleaning the oxidation on all this stuff. Or should I just replace it all with new and stop wasting time? If the latter, what do you recommend. Please give me direction - thank you!!! Quote Link to comment Share on other sites More sharing options...
WME Posted March 18, 2017 Share Posted March 18, 2017 The broken thingie is an auto reset circuit breaker. Available at most auto supply stores. Isolator is correct. The big wires on the side one should go the house battery and the other to the truck battery. Small black wire is OK at ground, small white wire should go to a switched 12 v source. No idea what the "alternator" thing is an 86 Toy should have an internally regulated alternator. Quote Link to comment Share on other sites More sharing options...
MaineErik Posted March 20, 2017 Author Share Posted March 20, 2017 I replaced the 40A breaker, easy to find at the local store as you said WME. I cleaned up all the contacts on the isolator. The cab battery now reads well on the 1st terminal of the isolator. The ground on the isolator is good. When I turn the key to "on" I can hear the solenoid click and there is 12+ volts at the small terminal with the white wire. However the voltage is only 1volt at the 2nd large terminal going to the coach battery. Can I assume that this proves the isolator is bad? If so, can I also assume that any continuous duty replacement isolator will work properly? How many amps should a new isolator be rated for? I'd still like to know what the "???" is in my photo. Quote Link to comment Share on other sites More sharing options...
WME Posted March 20, 2017 Share Posted March 20, 2017 Leave the small wires hooked up, remove the big ones and use an ohm meter to check resistance when the isolator is energized. Should be very close to 0. Any 75 amp or larger isolator rated for continuous operation will do for replacement. A 4 pole will need a ground, a 3 wire is self grounding Quote Link to comment Share on other sites More sharing options...
Maineah Posted March 20, 2017 Share Posted March 20, 2017 The rusty terminals may fool you. Regardless both large terminals should show battery voltage relay bad or not. Check each battery note the voltage then check the large relay terminals the voltage should be close to what each battery is. The only thing the relay does is connect both batteries together with the key on both terminals should have voltage with the key off it's a very simple on/off switch. There most likely is a second breaker like the one you replaced connected to the coach battery wire check the voltage both sides they should be the same. You will break the unit like you did the first one if it's bad or you try to clean it so just go ahead and get another one and a couple new terminal ends. To check the relay once every thing else is OK, Start the engine check the voltages both sides of the relay they should be going up and match both sides of the relay. Quote Link to comment Share on other sites More sharing options...
MaineErik Posted March 20, 2017 Author Share Posted March 20, 2017 I don't have the coach battery installed right now, it's in the garage on a trickle charger. But as WME suggested I measured the resistance across both large terminals (wires disconnected) with the key off and on. Off there measured infinite. With key on (and 12 V measured at small terminal) there was still anywhere from 600 to 1500 kohms of resistance. Once there also measured infinite until I tapped the isolator a few times with wrench which made the resistance numbers change quite a lot, but they never held steady or dropped to zero. I assume when you say the isolator should measure zero resistance (when on) you mean ZERO, right? FYI - The engine was left off, I just had the key in the off or on position for the test. Quote Link to comment Share on other sites More sharing options...
WME Posted March 20, 2017 Share Posted March 20, 2017 A good isolator will be in 5-15 ohms range. 600-1500k is way bad. With no load your measurements make sense. Quote Link to comment Share on other sites More sharing options...
Maineah Posted March 21, 2017 Share Posted March 21, 2017 Yep time for a new one. Beating on it and having it change is a dead give away. Quote Link to comment Share on other sites More sharing options...
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