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Towing - 5th-Wheels & Travel-Trailers 6.2/6.5 and Duramax towing performance? Towing accessories? Truck/trailer setup? Compare RV trailers? Trailer maintenance? Great destinations & vacations? Anything towing or trailer related.

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Old 06-15-2018, 06:46 PM
jerry598 jerry598 is offline
Join Date: Aug 2005
Posts: 190
Default When You Are Hooked UP

Wiring hook-ups to your pickup camper and maybe even a camp trailer can keep things hot under-hood, even with under-hood batteries disconnected.

I went to swap out a glow plug relay today. Disconnected the batt negative cables first and then went to wrench off the nut holding the hot wire side off the glow plug relay. Surprised me when I contacted the engine block with the wrench and got sparks. Took me a minute or so to realize that somehow the hot wire on the glow plug relay was still being fed by my camper's battery. That's in spite of the fact that everything in the cab was dead.

I don't know how it was wired because the dealer wired the camper hook-up for me. The hook-up feeds the camper's battery and keeps it charged when I'm driving, but however the dealer hooked it up also keeps that glow plug relay hot. Once I disconnected the camper battery all went OK with the repair.
Black 95 6.5TD, 929 block, 148k miles, 45k on IP, 24k miles on self-rebuilt engine done in '09, 6 L&S Full-torque inserts in outer main crank holes, Clearwater heads, Fluidamper, rebuilt NV4500, 3" downpipe, 4" exhaust, no cat, dual T-stats, 9 blade fan, spin-on 180 degree clutch, Heath hi-flow water pump and turbomaster, PMD relocated, OPS relay mod, Heath PROM upgrade, and Kennedy headlight harness upgrade soon. Now use semi-syn Lucas 2-cycle oil every fill-up which fixed DTC 35-36 codes (code comes back if I don't use the Lucas - dino 2-cycle oil does not work!).
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Old 06-15-2018, 07:26 PM
DmaxMaverick's Avatar
DmaxMaverick DmaxMaverick is offline
Join Date: Apr 2001
Location: CA
Posts: 12,190

Yep. That's how that works. The only way around it, if wired correctly, is to isolate the RV harness from Batt+ with an isolator relay. I normally recommend this, unless you are particularly fond of dead starting batteries when someone leaves on one little lamp.

(normally) The GP Batt+ lead (large wire) is always hot (through a fusible link from the batteries). Only the relay coil lead is powered through the ignition switch.
1985 Blazer 6.2
2001 GMC 2500HD D/A
2014 Chevy Cruze Diesel - Fabulous car, no problems at all, but sold Nov. 2016 @ 55K miles.
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Old 06-18-2018, 11:01 AM
JeepSJ JeepSJ is offline
Jeep Freak
Join Date: Sep 2003
Location: Feeniks, Aridzona
Posts: 1,114

Yep. I wired mine through a 40a relay that is triggered when the key is on the "run" position. That is from experience when I had a trailer with a bad battery and it drained the truck battery overnight.
1987 Jeep Grand 6.5 in process...diamond block, 18:1's, other goodies...

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