Again, this is my '91 5.2 TBI (which has a new fuel filter and will get shaken down in the next few days).

I'm adding an electric trailer brake controller. I need a min. 20A circuit (two axles, four drums). Where's the best place to get a switched +12V?

 

What kind of trailer are you planning to pull? What's it weigh?

 

Two-horse trailer, probably only loaded with one. Don't know what it weighs. Not great distances or many/big hills.

 

I've got a distribution buss (out of a late-80's early 90's Chevy/GMC pickup) that my main cable into the cab is fed through; that feeds a secondary fuse block. I'd use that to feed the relay, and switch a relay off of almost any switched 12V feed (such as, possibly, the switched feed to the radio).

That's my take.

RwP

 

I wasn't looking to get that elaborate about it. I was hoping that there's a convenient spot to take off a switched feed without adding another relay, etc.

 

A 20A switched feed?

There may be; but !I! would not try it.

These trucks are old enough, they weren't designed with that kind of reserve capacity.

Besides, I've long been a proponent of "use relays for the real current" *grins*

(I've got that buss bar feeding the two relays, via the after market fuse block, that drive my low and high beams; I'll be adding a relay when I finally get my fog lights in to the pair on the radiator core now.)

Plus, you're going to have to run the power to the back anyway; I'd rather it be on its own fuse in case something hinkey goes on like a sharp rock piercing the wire and shorting it out. (Actually, I'd use one of the mini-ATC sized circuit breakers, but that's me.)

My other suggestion, then, would be to grab the factory service manual and decide where you want to add the extra load.

RwP

 

Sure - as an EE I understand the issues, and (of course) I've got a fuse in the circuit. I'm just trying to avoid a bunch of extra work for an addition that's going to have a really low duty cycle. If there isn't a suitable spot for adding this feed, I'll probably just go straight to the battery, but my concern is the quiescent current drawn by the controller. I have no idea what it is at the moment, as it's not part of the manufacturer's published specs. Guess I'll just have to slap a meter on it and see if it's going to be a problem. I can always tart this up with a relay later, but for the moment I just need something serviceable. This truck is a beater, and not where I'm trying to do work I'll be proud of.

 

a bus bar or relay controlled battery feed is the proper way to do this.

otherwise check the fuse box for switch feeds for options you vehicle doesn't use...ie maybe the abs if your not abs equipped....and use that feed as long as the wiring can carry the amperage required.

when you run your constant 12v power and brake controller power feed to the rear of the vehicle....go to gregg's distributing or allied....they have ready made wiring wrapped in casing/loom. you can get in 3 wire or 5 wire configurations and any gauge you need. cost to run it front to back is $16. A lot cheaper than buying wiring and loom separately; and you don't have to fit the wiring into the loom.

 

I wish I'd known about Gregg et.al. having harnesses available - might have been cost-effective, tidier, etc. I'll have to take a look.

I think I've found the right balance between doing this The Right Way and my innate laziness: The fuse/relay box under the hood that holds the starter relay, AC relay, etc., has three vacant sockets, so if I hit the wrecker and snag another one for a couple of bucks I'll get the little white clips that hold the quick-disconnects in place under the relays. Having a location for the relay and not having to figure out where and how to mount it is about 99% of the hassle.

 

That's definitely the right way to go, and I'm back from the boneyard.

Problem: I don't have the factory TSM for this thing, and the Haynes manual just doesn't describe the box accurately enough.

Can anyone direct me to an online source for the factory schematics? I don't need everything, mainly just the drawing for this bus/fuse/relay box by the driver's side shock tower. Again, this is a '91 Dakota 5.2/318 auto 4x4.

thx.mch.