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TOTM January 2011: Electrical Wiring

GrimmJeeper

GrimmJeeper

NAXJA Forum User
Location
Gardena, CA
For this month's TOTM let's have a discussion of electrical considerations on a race vehicle (this information will still apply to a prerunner or toy so I think it's a valid topic ;)). I'll start with some suggestions of topics to discuss that I have been wondering about, and a question. Feel free to ask more questions, suggest more topics, or add to the discussion as you all see fit.

These are things I would like to know more about:
-special considerations for wire connections
-getting hot leads through metal reliably
-switches (brands, metal vs plastic, etc)
-gauge wiring (new leads vs tapping into the stock harness)


And my question:

I've heard repeatedly that relays have no place in a go fast type rig, and that they are prone to failure from vibration or shock from hard hits. Is this true?
 
Solid State Relays are pretty decent these days. I would probably use regular relays, but a bolt-down type with screw terminals rather than the standard plug-in type. Might consider looking into mil-spec parts, a lot of surplus dealers sell them.
 
GrimmJeeper said:
Circuit breakers. Just wondering if there is any truth to it :dunno:
Click to expand...

Circuit breaker /= relay.

I don't see how you would sub a circuit breaker in for a relay. The point of the relay is to allow you to keep the load wiring short, and not have to use a 50A switch in the vehicle cabin.

What Ken said is true, I'd just go with bolted on relays, preferably something mil spec that is sealed to prevent dirt/water intrusion and with binding posts to secure eye rings, rahter than slip fit spade connectors.
 
Run the switches on the ground legs. Really cleans up the wiring, and you don't have a bunch of power wires that can short out under your dash. If something does short, it will just turn that accessory on, and you'll know exactly where your problem is.
 
Loose_Nuts_Enterprises said:
Run the switches on the ground legs.
Click to expand...
That would make the whole harness "hot" all the time. Is that really a good idea? Everything on the truck would be powered unless the battery is disconnected.
 
Loose_Nuts_Enterprises said:
Run the switches on the ground legs. Really cleans up the wiring, and you don't have a bunch of power wires that can short out under your dash. If something does short, it will just turn that accessory on, and you'll know exactly where your problem is.
Click to expand...

one problem with this is you get feed back from components like cooling fans . if you run an indicator light it will come on ,anoying as all hell too lazy to change mine blak tape workes well for now . in order to fix that problem you have to run a diode in line. just one more thing to fail.:anon:
 
If you use a quality switch rated for the amp draw that you're pulling there is no need for a relay, making troubleshooting and repairs much simpler!
 
_87_XJ_ said:
If you use a quality switch rated for the amp draw that you're pulling there is no need for a relay, making troubleshooting and repairs much simpler!
Click to expand...

It's hard to mount a throw switch like the one they used to light up Frankenstein.

Relays serve their purpose well.

Circut breakers < fuses
 
best thing about circuit breakers is if you get self resetting ones when you have an intermittent short the breaker will cycle on and off allowing temporary function of the circuit. makes it nice when you cant stop and diag the problem . one thing ii always have to remember is the old saying "Keep it simple stupid" when diagnosing electrical:anon:
 
I absolutley agree, there comes a point when a relay is neccessary!


FatCity Ryan said:
It's hard to mount a throw switch like the one they used to light up Frankenstein.

Relays serve their purpose well.

Circut breakers < fuses
Click to expand...
 
simsfamxj said:
best thing about circuit breakers is if you get self resetting ones when you have an intermittent short the breaker will cycle on and off allowing temporary function of the circuit. makes it nice when you cant stop and diag the problem . one thing ii always have to remember is the old saying "Keep it simple stupid" when diagnosing electrical:anon:
Click to expand...

Except for when the breaker heats up and melts.
 
Relays - good. I don't know a single Trophy Truck or unlimited buggy that isn't using relays.

Circuit Breakers - Manual resetting type. Nothing is more annoying during a race than something that keeps cycling on and off. Well, there are some things more annoying but this is pretty annoying. If you have a breaker trip, it means you have a problem - whether or not you stop and diag depends on the circuit and where you are at the time.
 
GrimmJeeper said:
These are things I would like to know more about:
-special considerations for wire connections
-getting hot leads through metal reliably
-switches (brands, metal vs plastic, etc)
-gauge wiring (new leads vs tapping into the stock harness)
Click to expand...

Wire connections - avoid spade terminals, use ring terminals whenever you can. Use the uninsulated, crimp, then solder, then shrink-tube. The crimp gives a good mechanical connection, and the solder improves the electrical connection. The shrink-tube takes the physical load off the copper and onto the insulation.

Hot leads - most circuits just go through a hole that is protected with a grommet. Heavier stuff gets a feed-through.

Switches - metal, sealed marine or mil-spec. No plastic. Dust will get in wreak havoc on non-sealed switches.

New leads - always. Stock harness is barely adequate to handle stock loads.
 
DieselSJ said:
Wire connections - avoid spade terminals, use ring terminals whenever you can. Use the uninsulated, crimp, then solder, then shrink-tube. The crimp gives a good mechanical connection, and the solder improves the electrical connection. The shrink-tube takes the physical load off the copper and onto the insulation.
Click to expand...
Beg to disagree:

Yes, use ring terminals. Preferably, use aircraft grade terminals with brazed barrels. Also use an aircraft-style stripping tool, which will not kink, nick, or scrape the wire. Crimp with a quality crimping tool. This is actually important. Poor crimping can cause a hard-to-trace intermittent problem. Do not solder joint. Shrink-tube to insulate and remove stress from wire between insulation and terminals.

In aircraft electrical, they never solder floating connections. In a high-vibration environment, the wire will work harden, crack, and break right where the solder stopped penetrating down the wire. For a connection that just has to be soldered, get a ring terminal with a long shank between the barrel and ring, solder the end of the wire to the shank in front of the crimp. The crimp area itself stays un-soldered.
 
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