This is a list of things that in our experience, reduce the risk of having to send a harness back for repair. Most wiring problems aren’t discovered until they actually begin causing an issue while you are trying to enjoy your race weekend. Our goal is to help avoid those situations and keep you up and running.
This document contains a few NASA Prototype (NP01) specific instructions, as well as general wiring harness best practices.
When installing your engine harness, start with the fuel rail and work fore/aft. As seen in the picture, the hard points on the harness should be attached to the supplied threaded holes in the fuel rail. This centers the harness and helps ensure that it aligns well with all of the connections in the rear of the car.
The harness located by thread holes.
The relay mount is built into the connector.
Backside of NP01 Switch Panel
It’s fairly common to see harnesses tied down at 9″ intervals, however this is only a guideline. Many areas require different tie down intervals based on the flexibility of the harness and the risk of damage.
Keep the harness away from sources of heat, around or above the exhaust is bad. You can get away with under the exhaust if you’re careful.
This lambda sensor connector was a bit too close to the fire.
Put shrink over unused connectors to keep out dirt, corrosion, grease, and other contaminants. When electrical tape is necessary we use the self fusing Silicone tape. The vinyl electrical tape leaves residue and get slimy when exposed to heat and some typical automotive cleaners whereas shrink does not.
High-temperature, glue-lined shrink insulation over a connector.
The NP01 alternator torque is relatively low at 58in-lbs, ensure that you don’t overtorque the nut. It’s also a good idea to secure the wire to the alternator frame using a zip tie.
Alternator Torque Specifications
Any NP01 switch with a number on the end serves as both a switch and a breaker. When tripped, the switch will move to the center position in response to an overcurrent condition.
NP01 5 Amp Breaker, 7.5 Amp Breaker, and Toggle Switch
Along with insuring proper installation of your NP01 harness preparedness is key. Visit our NP01 specific parts shop and start building a collection of spares. Along with the listed breakers, switches, and connectors listed we also stock parts for this harness like DT pins & connectors, wire & shrink, boots, and labels. Please contact us for any special order items.
Please contact firstname.lastname@example.org if you need any harness pin-outs.
General Harness Wiring Tips and Tricks
Don’t hang your harness from the switches and breakers themselves, make sure it’s tied down to the panel like the example below. This reduces the number of problems and with the connections. As a bonus, it makes all of the connections easily serviceable. Notice that all of the screws are visible, all of the wires are curved and the harness is securely tied to the panel with multiple large zip ties.
Securing wires, breakers, and switches
When tightening or loosening the screw on switch breakers, hold the metal lug to avoid snapping it off.
Most harness issues (ignoring accidents and fires) occur at the connections. And connections are heavier than an equivalent length of harness. So don’t invite problems by supporting the heavier bits by the fragile bits. Tie down the connectors.
Tie down heavy parts; don’t hang connectors off the harness. Most harness failures occur at a connector and adding strain to the harness will accelerate the process.
DTM Connector Zip Tied to Chassis
There are multiple common mounts for harnessing available. From left to right you have a P-Clamp (aka Adel clamp), a saddle mount and a glue tab.
Zip Tie Mounting Options
Copper wire work hardens with stress and strain. Shaking or vibrating copper causes it to become more brittle, which in turn makes it’s more likely to fail. Twisting wire and strain relieving connections will help mitigate negative effects, but as an installer you ultimately want to reduce vibration and shaking as much as possible. You can find a strain relieving section further below in this document.
Heat and vibration can crack even high quality mil-spec wire.
Heat-related fatigue and cracking example
The harness should be tied down, especially any heavy sections, but there is such a thing as too much. Running the harness straight from the fender to the side of the valve cover in a car with rubber engine mounts may be an obvious example of a recipe for disaster as the engine repeatedly pulls the wires tight. Another amusing example is running a wheel speed wire straight from an a-arm up to a fender. However, the same thing can happen to a lesser degree as parts vibrate or the car is serviced. Don’t run the harness in a straight line where possible, give it some curves where flex can be absorbed without causing additional strain. As a bonus, you have a bit of extra length if the harness needs to be serviced or shortened.
Elongated wires for future changes
For the nickel, mil-spec connector at the driver’s left shoulder, Elan is using an O-ring to restrain the connector. This provides the most cost effective means of supporting the connector while allowing it to self align. The heaviest solution is a mil-spec nut plate. We typically tap the connector for 6-32 screws. Be mindful of thickness of screws heads and panel. They may prevent the lock ring from locking.
Tapping a Millspec connector
Never stick a multimeter probe or anything else in a pin unless you know the pin is resistant to stretching, mil-spec ones will be OK, OEM ones won’t. The over-sized probe risks loosening the terminal and creating an intermittent connection.
Incorrect method of testing connector
In a motorsport environment the typical weak link with a standard relay is the spade connections. Spade connectors can get contaminated or loosen. Either instance will make poor contact and perform poorly. Over time this poor connection generates heat, resulting in failure of the connector and/or relay. To avoid poor connections, ensure that oil and contaminates are kept away from spade type connectors (and any connectors for that matter). A common way for spade connections to become loose is when relays are rocked back and forth during removal. You can also avoid creating a loose connection by prying or pulling them straight out.
The picture below shows a relay connection that overheated and melted the terminal into the holder. Notice the gray finish verus the shiny finish on the normal terminal.
Harness flexibility is achieved with proper planning and wire twisting. Bundles of wire should be gently hand twisted before being tied together or placed in heat shrink. Be mindful of creating stiff points. We have seen many harness failures through the use of the stiff RayChem boots and improperly secured wire. The wire always breaks right where it exits the boot.
When putting a boot over a connector the wire should be twisted in a way that pulling on the connector will not stress the wire.
If there’s a zip tie on the harness holding a boot on, don’t cut it off! In hot environments, shrink has a tendency to back off the connector if not held down properly.
Zip Tie Sealed Boot
Zip ties are a crucial part of a harness’ durability especially in extreme environments.
Though not recommended, if you need to cut off a zip tie, always try to cut off the lock as opposed to the strap. This reduces the likelihood of snipping a wire.
Properly cutting a zip tie
Don’t do this!
Improperly cutting a zip tie
A good crimp is achieved with proper tools at the proper settings. Sometimes connections can be forced (improper tools or crimping a wire too tight or too loose) but their longevity and current handling come into question, even if it “looks OK”. A proper crimp on a barrel type connector will have wire showing in the inspection hole with about a half wire diameter of gap to the insulation. A proper crimp on a stamped connector needs to have bare wire showing on both sides of the wings. Grommets should be used if supplied with the connector. The wings should curve down into the wire in the shape of a lowercase ‘m’. All crimps should be tested with a firm tug to ensure strength.
Use quality materials whenever possible. The ignition coil and harnessing below survived a fire. The harness was not replaced until after the car qualified on the pole!
Toasty Ignition Coil
Have you ever been scraped or cut by a zip tie that had a little piece leftover from when it was cut? Invest in a good set of wire cutters that make a flush cut.
Notice the cutters on the left have a flush cutting surface, as opposed to the ones on the right that have a beveled cutting surface. The bevel is what leaves that little bit of zip tie behind to cut you!
Flush vs. beveled wire-cutters
Don’t use Simple Green to clean your harness, it’s corrosive and will harm the connectors.
Note the grey/green corrosion on this connector.
Simple Green Residue causing corrosion
Are you pushing your connectors to their limit? Dielectric grease on the contacts reduces the possibility of corrosion when the connector gets hot or where water may be present. It also helps dampen vibration commonly seen with high RPM, solid mounted, motorsports environments. Higher quality connectors in less abusive environments may not require grease.
CRC, the preferred Dielectric Grease of Electron Speed
Don’t cross your harness with any stainless braided hose. Since it is conductive, it will short the first conductor it reaches as it saws into the harness. A common solution is to use a zip tie to maintain a gap where they cross.
Don’t tie sensors or harnesses down to hoses, they tend to be flexible especially under load.