1990 D350 Trailer Wiring

[surfbeetle]

My Dad has a 1990 D350 that he bought new back in '90 but did not opt for the towing package. Back then he simply added a drawtite hitch and spliced into the tail light wiring for the trailer recepticle and thought that all would be fine. Over the years, he has had to do the headlamp switch replacement and he has had two batteries explode in the truck. Is there a way or preferably a kit so that the wiring can be added like the factory tow package wiring so the headlamp switch won't keep burning up? Thanks in advance.

 

[ARhine]

There is no off the shelf kit that I know of. The best way is to rewire the trailer wiring to feed power through relays instead of drawing from the headlight circuit.



Have not done this on my truck either yet. I need to though since the previous owner spliced into the wiring at the back of the box and now everything is getting corroded up.

 

[surfbeetle]

The problem is my father didn't have trailer wiring that ran the full length of the truck. He tapped into the wiring harness for the rear taillights under the bed. We were hoping to not have to make up our own wiring harness, but connecting up front with relays definitely seems like a better way to go. Thanks.

 

[ARhine]

The way I was going to do it was:



Get 3 relays from the salvage yard. The relays on alot of newer GM cars are nice weather sealed units and are what I usually grab. Once a year I go in and scavenge the "to be crushed pile" and get a box full of them and other usefull connectors for $5.



I was then going to wire into the light wiring either at the firewall or under the dash and mount the 3 relays (left T, right T, and tail) under the hood. Then get a roll of that 4 conductor wire used to wire trailers and run it from the relays to the plug on the back of the truck. Hope that helps.



Get some good adhesive lined heat shrink and such from www.waytekwire.com or similar to fix up the existing wiring at the lights and for connecting to the pigtails on the relays (if you use salaged ones like me).

 

[MMiller]

I don't know if the 90 is alot different then my 93, but I bought the trailer light kit from Walmart, or a parts store. All I had to do is unplug the factory tailight harness and plug in the "T". This "T" is made just like the factory plug and has a flat 4 plug coming off it. This I then plugged into my round 6 that had the flag 4 plug made in it. Then all I had to do is run a wire from my brake controller to the lead on the round 6 plug. I need to run a hot wire back to the bumper, and hook it to a relay triggered by the parking lights, but have not done so yet. I suppose I am on borrowed time with my head light switch.



All, except the trailer brake control wire, was plug and play, weather tight connections.



Michael

 

[surfbeetle]

Michael,

That's about what we did only we did not have the T connector, we spliced and used solder and shrinkwrap. So I would imagine that you are on borrowed time. It would really depend on amount of draw that the trailer running lights places on the truck as to how soon the switch gets burnt out.

Thanks.

 

[EZeis]

Reese and drawtite make a kit for your truck that plugs into the factory wiring at the tail lights and that will give you basic trailer lights (4-flat). Then you can buy a power isolator called a Modulite that plugs into the other harness's 4-flat and draws power from the battery instead of the trucks undersized wiring and headlight switch. Both items are plug and play (other then running the included battery power cable to the front of the truck) and it's weather tight and a good set-up.



http://www.drawtite-hitches.com/electrical/modulite.htm

http://www.drawtite-hitches.com/electrical/t_connector_all.htm



Earl

 

[MMiller]

http://www.drawtite-hitches.com/electrical/t_connector_all.htm



This is what I used, thanks for the link Earl. The only protential problem I see is with the running lights on the trailer. This I can see taking out the headlight switch. I would think the turn and brake light circuits will be fine. I think as long as the connections are good, and the ground between truck and trailer, the switch will last longer, ie less resistance.





I think I will need to look into the power isolator. That looks like the easiest, cleanest way around the problem.



Michael

 

[surfbeetle]

Thanks. The Drawtite stuff looks like the best/easiest way to go.