I have a 97 Dodge Ram 3500 DRW Cummins diesel w/factory tow package and am
pulling a 27 foot fiver.
My question started on the RV forums with the query; should I disconnect my
truck connector when hooked to either shore power or using my external
Many of the replies referred to a "tow relay" that only operates when the truck
is running.... that is what is supposed to connect the truck's battery power to
pin 4 of the connector to charge the house battery in the trailer.
Well, my service manual for 97 does not show that the tow relay works in that
manner. The tow relay operates via the headlamp switch to provide power to the
trailer's running lights and license plate light via the connector. I checked
this out with my multi-meter and it does what the manual states.... in fact,
the tow relay operates ANYTIME the headlight switch is in park or on position.
I also see NO sign of any type of isolator in the circuit.
Can someone confirm that Dodge only uses a tow relay for that function which I
have described? I would hate to wake up on an interstate rest stop with
battery problems in the Dodge.
The relay only controls the lights on your Dodge. In answer to your
original query, for an overnite stay, no harm will come to your truck or
battery by leaving the towing harness connected provided the onboard
converter/charger in your RV is operating properly. This applies to either
shore power or genset.
Hope this helps!
I can't verify the tow relay as you asked, however, I'll offer the
following based on experience:
I've got a '98 and have never had the problem you describe. If you
are just pulling in for the night and turning on some lights for a
while in the evening, it shouldn't be a problem.
IF you are running the heater all night or running the A/C or
microwave through an inverter, or some other high power appliance, you
could have a problem.
I leave mine plugged in whenever I'm hooked up regardless of whether I
have shore power or not.
'98 3500 QC 4x2 Cummins ISB, Auto, 3.54:1,
Driftwood with Leather and all the heavy duty options.
'89 Nu-Wa Champagne Edition, 34 foot Fifth Wheel.
I have friends that disconnect from the truck just to be safe... that's probably
a good idea, but so is obeying all speed limits.. *g*
We've been pulling our RV since 2003 and the habit has become: If you're not
unhitching the trailer, don't mess with the chains or the plug... less chance of
trying to leave without reconnection..
never had a problem with electrical, even at "less than ideal" power hookups..
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