More than you ever WANTED to know about the relays & electrical system of a REV sled 
Do a search overr on DOOtalk and you'll find a bzillion threads about the relays on SDI (and non-SDI) sleds (and the issues related to 'em)... Here's a "one post catch all" that hits the majority of the highlights... and dispells most of the myths.
Sure... this is one LONG-*SSED post... but I'll guarantee that if you read it & have sense enough to digest it, you'll be able to trouble-shoot & figure out near any relay-related electrical issue (and some non-relay related ones) that may crop-up on your sled.
I suppose question #1 on everyone's lips is..... WHAT RELAY WORKS THAT DOESN'T COST $30 AT MY DEALER?!?!?!
The simple answer... just about any one that'll fit in the socket & works without issues in your sled when you're riding it.
Really... it IS just that simple... if you spend the 3 or 4 hours reading all the threads on the issue you'll uncover discussions of some relays being "better" than others (true, to a certain extent), making sure there is a "diode" or "resistor" in the relay used in SDIs (not true), and the minimum current capacity ("sort of" true, but not a deal breaking critical issue in our application... most of the time).
There are guys that have sought-out "certain" relays like BOSCH for example... and had great success with them... and others that have gone to the local PEP Boys, VIP Auto, or other local area discount auto parts store... walked over to the section where they sell fog lights, switches, and other electrical accessories... grabbed one off the shelf... matched it up with the bad one they brought with 'em... plugged it in and gone sledding... and still have the same relay in it to this day... no issues... heck, I'd be willing to bet the auto parts section of Wal-Mart even has 'em.
And those will be cheap Chinese 20-amp (probably) relays.
OK, I know... not the answer you were hoping for... but I wanted to dismiss a lot of the high current/certain brand/certain type/magical mystery contents cube/etc technical mumbo-jumbo as to what does and doesn't work... you know... dispense with the "myths".
Myth #1... You need a relay rated for 40-amps or more.
I've had one of those el-cheapo
"American components... Russian components.... ALL MADE IN TAIWAN!!!!!" type (sorry couldn't resist... lame "Armageddon" reference) 20A relays zip-tied up under my sled since back in December.. grabbed it off the rack at PEP Boys.
Ok, sure... the specs on the stock Doo relay are 40 Amp... and if you want to trace the circuits and do the math...
E-Start Non-SDI relay feeds 1 30-amp fuse and 1 5-amp.
Manual-Start non-SDI & SDI "Load" Relay feeds 2 20-amp fuses.
SDI "Run" Relay feeds 4 5-amp fuses and 1 10-amp.
On the surface that means we have a theoretical maximum of 35, 40, & 30 amps respectively... but...
If you've ever designed electrical circuits you have to "overfuse" it, so to speak. A 30-amp fuse that has a constant 29.9 amps of current going through it isn't going to last very long... so most are calculated for a constant load of 50-75% of the fuse rating and rounded up, depending on application.
Take your headlights for example... which are run through one of the 20A fuses... let's do "worst case"... we'll figure your voltage regulator is getting a little "hot" & is putting out 14 volts when you've got her wound up... even if you've put 2 100-watt high beams (which are right around 1.5-ohms) that's still only around 18-1/2 amps of current.... just over 10 amps for the stock 60-watters @ 13.5 volts is more realistic... toss in a 1/4-amp for the high-beam indicator (and that's probably overkill) and you barely crack 10-1/2 amps... on a 20-amp fuse.
(Note: at speed the charging system in your sled is somewhere between 12.75-13.5 volts normally)
Still... if you're the skittish type and want to be safe, or if you have installed higher wattage headlights... on a Manual-Start non-SDI, or for the SDI "Load" relay, you can ask (or check) if what you're getting is rated for at least 30-Amps... but, given the reality of the circuitry currents I don't think it's a deal breaker... you'd have to ride around all the time with the (stock)high-beams on, grips & thumb-warmer on high, with a heated visor and some other accessory (like a GPS) plugged in, AND be dragging the brake all the time to get up to 20 amps consistently.
Still not convinced?... OK... how about this...
What's the maximum output, in amps, of a 360-watt Doo magneto?
Do the math and get back to me... here's some help if you don't know "Ohm's Law"...
http://ourworld.compuserve.com/homep...en/ohmslaw.htm
(Yes, I know you SDI owners have a 480-watt mag... & you also have TWO relays to feed... not just one)
Myth #2... You need a relay with a diode/resistor/magical mystery component inside.
Take a bad stock Doo relay apart and you won't find anything but a relay... which is basically just an electro-magnetic switch... there's no diode and/or resistor and/or anything else to control any voltage spike/lightning strike/Act of God in there... it's just a dumb on/off switch.. that's all... even in the SDIs.
and finally...
Myth #3... You should never "tap/rap" on a relay to test it.
Well... if you're talking about the average relay found inside any of the handy-dandy electronics toys you have around the house and available at your local Radio Shack that's true.... but we're talking about relays that are supposed to be made to survive in an automotive application.
Now, if you bash it with a hammer it's not likely to work anymore... but if it can't survive me tapping on it with a screwdriver handle (or maintain contact connection... ala the mystery SDI "cutout" issue) it's not likely to survive in the sled much longer anyway... and could very likely be the reason it cuts out when I bash a mogul... or hit that certain vibration frequency & magnitude at 7500RPM on a hard pull.
Here's a quote from Panasonic's literature on their
High Power Automotive Relays
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Quote:
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- High Shock Resistance for Drop Test Requirements (2 Meters - 6.6 Feet)
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And this from the datasheet...
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Quote:
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SHOCK RESISTANCE - Destructive - Min 1000m/s[sup]2[/sup] (100G)
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... I say it should be able to pass the "tap test" easily.
OTHER RELAY FAQs & GENERAL INFO/TROUBLESHOOTING:
Q: Why do they seem to fail more in sleds than cars?
Well, think about that for a second... IMO we're subjecting these things to a FAR harsher environment in a sled than they were envisioned for when they were designed for your average car/truck.
Just the frequency and magnitude of vibration alone is FAR over and above what it would ever see in the normal automotive world... sure, Doo COULD spec out a much tougher relay just for sleds & have 'em made... but, supply and demand weighs in... what do you think THAT relay would cost? Heck, we have enough cheapos around here that cry about having to spend a few cents more per gallon for premium fuel for a P-Tek... or a few bucks more per gallon for syn-blend oil for an SDI... never mind a $75(or more, likely) relay.
IMO it's as simple as the fact that we're shaking these things to death.
Now, are SOME relays going to last longer than others.... YES, absolutely... you DO get what you pay for in some cases... question is... what do you want and/or need for how you ride.
If a relay cutting out is going to cost you a race or leave you stuck on a steep mountainside in waist deep powder... I'd definitely shoot for something a little better quality than what you can get for 3-5 bucks at your local discount auto store. (Bosch & NAPA seem to be the top contenders there.... Ford also has one that works & the "Standard Motor Products" brand found in many GM vehicles isn't a bad choice either)
But if the only thing it means is that you have to get the spare out of the trunk on the trail somewhere and swapping one out on the trail doesn't bother you... grab the cheap ones if you want... they do work... the choice is yours.
(cont. next post)