Blue Wire in Battery Compartment

[Jay Kurrle]

This is my first post on the forum so if I do something wrong please
tell me. We recently replaced our chassis batteries on a 2000 Alpine
Coach. There is a blue wire in the battery compartment and need to
know if this goes to positive or negative. It is long enough to go
to either. Also the voltmeter on the dash is not working. If anyone
can help it will be much appreciated. Our wiring diagrams do not
show a blue wire.

Jay and Jean Kurrle

[SteveS]

Jay - I presume you can't trace it back to a source. My first guess is that it is coming from the Echo charger. If so, you need to know if it is the house battery output or chassis battery output. Do you have a red or orange wire also coming from the same location as the blue wire? Any additional information would be helpful.

[wa8yxm]

If you have a wire, hanging there, you really should trace it to it's other end to find out what it is, It might be Positive, Negative or.. Something else (Switched)

Step one is a multi-meter, with the rig unplugged measure from
negative battery (Black) to positive battery, note voltage (Should be 12.x)

Now move the red lead to the suspect wire, see the same voltage? it's a positive wire more than likely, could be switched though. Jump to "Positive" below

See zero: Start the rig, See 13-16 volts? It's the charge lead from the alternator, hook to positive

See Zero: Plug in the rig, See voltage, Charge lead from converter, Connect to Positive

See Zero: It is either a ground or load lead, Trace the wire or.. Apply power via a light blub.. (See light bulb below)


{POSITIVE}

If the wire shows positive it may be power to something that used to be in the battery compartment, You really need to trace it out.

One way is to operate every switch, and/or remove every fuse

Another way is to use a wire tracker from Harbor Freight, However the only way that is 100% is to physically follow the wire.

And that's the best method.

[Jay Kurrle]

Hi SteveS,

Thanks for response to my post. Yes we do have a red wire coming from same location. The blue wire is only long enough to reach the Chassis Battery so just need to know if positive or negative. The wiring diagram shows no blue wire.

Jay and Jean Kurrle
2000 Alpine Coach

[takepride]

A possibility is a towbrake setup. SMI/US Gear uses a blue wire and a red wire that runs from the coach to the toad. The red is for constant power to the toad, the blue to send a signal from the controller (at dash) to the toad. They are normally in the same harness and terminate at the rear as an umbilical connection (or wired into the OEM tow plug).

[Dave Fernandez]

Hello & Welcome Jay:

The Blue wire may also have been from a trailer brake controller. I use a trailer break controller on my Alpine and on the Yukon and they both use Blue wire to the Trailer plug. Since your coach is used the dealer or previous owner may have removed for use on another vehicle.