The International Cessna^® 170 Association

By some strange cosmic alignment, I started having exactly the same trouble as Doug with the master switch not powering up the electrical system.

I used my VOM to check out the cockpit switch, and it showed continuity.
Bad master relay/solenoid! I did some initial checking at mycessnaparts.com and they want a whopping 336.00 bucks for the thing! I've already removed the solenoid...it looks like something off a Ford tractor, and probably is. Anyone have any alternatives? Please? ...Russ Farris

If the coil in the solinoid is good, it can be repaired by cleaning the contacts. The plastic cover can be removed by dissengauging the spring clips. and the contact bar can then be cleaned with croakcus cloth.

Whoa... that makes three... you, me, and russ murri. The cosmic powers that be must be conspiring against our electrical systems

Since my solenoid was replaced last May, I'm thinking my problem is the switch or some other wiring issue. I'm still going to check the solenoid anyway. I'll report back under my "Piano Key Switch" thread when I find out what's going on.

Well, the coil is bad...open circuit. So this relay is Tango Uniform. It only looks about 50 years old, and probably is.

Aircraft Spruce and Specialty shows a Master Relay, P/N 111-226 "used on production aircraft, applicable to all homebuilts" for 16.95. Legal to use on my 170? Or do I take the old one to NAPA and try to match it up; I'm sure it's some kind of off the shelf part. I'm still stunned over the 336.OO dollars...confirmed by an A & P friend of mine with a Bonanza. It's the same relay, and the same price from Beech.

Something still tells me that it's the same as a 1952 Studebaker truck, or whatever...I had the thing apart and it is no different than an automotive relay. Ideas??? Russ Farris

Doug...not to be nosy, but how much did you pay for your solenoid? Russ Farris

Russ, No problem... $26.40. It looks similar to the one you found in A/C Spruce (p/n 111-226). I usually buy my own parts, but I didn't buy the solenoid, so I don't know where my mechanic picked it up. My log entry states "... Replaced master solenoid S1579AL....", but the service receipt lists it as S1579A Contactor (no "L" at the end). Don't know which is the correct part number, but maybe that helps a bit?

Just did a lookup on http://www.iwantcessnaparts.com and found Contactor S1579A2 (instead of S1579AL - perhaps both of my records have typos?) for 28.60. I ran the original part number from the C170B IPC and came up with a contactor for 372.00 - yikes!

Hey Guys,
If this is for the master switch relay, it not like the old pickup starter solenoids. The starter solenoids are for only short contact time only, the master relay has a coil that is made for long time contact and won't burn up the coil being on all the time.
John - n3833v

Thanks John, yes it is the master (battery) relay/contactor/solenoid. I was being a little tongue in check about it being a Studebaker part...

OK, this is what I have determined. The original, four post Cutler-Hammer relay is available and very, very expensive. I called several Cessna dealers, and the price is a staggering 372.00!

It is the same solenoid used in early Bonanzas. From the vintagebonanza site I found the same relay at two electrical suppliers for "only" 175.00. A little like getting beat up only once a week instead of every other day.

The original 4 post relay has a jumper wire, running from the postive battery side to one of the smaller posts, so that the coil has power. This circuit is completed when the Master switch in the cockpit is turned ON (actually, to ground) powering up the coil and closing the contactor.

On the newer style relay, like the one Doug has installed in his airplane, there are 3 posts - two large for the battery and starter, and one small, for the ground wire to the Master switch in the cockpit. I'm assuming this small post is powered when the battery is connected.

Now, as I think I understand things, I should be able to use the later style 3 post, solenoid like Doug did, with no modification to the wiring whatsoever. Since the new style is only around 30.00 bucks, you can understand my interest...If anyone out there can confirm this, I'd appreciate it. I guess George must either be deathly ill or out of town, because I would have expected to hear from him by now. Tom Downey in particular...am I correct in my reasoning on this? thanks guys, Russ Farris

Call Gene at AvAlaska in Anchorage, 907.248.7070 They are a Cessna dealer, and are very helpful.
PN S1579A2 Under $30

Kelly

The master relay shown on page 376 in the Spruce catalog that sells for $16.95 is the standard and proper one to use.

At $16 per unit, I would not even bother to rebuild the original unit, but if you do elect to refurbish/clean the original unit, I have found that adding a thin coat of "conductive grease" to the contacts will preserve them from arc damage as well as lower the electrical resistance. This conductive grease is available at Lowe's or Home Depot in the electrical department.

Thanks John, that's a good idea...the coil is bad on the old one so it's junk.
I'm ordering a new one from Aircraft Spruce tommorow...Russ Farris

Thanks, Dick! It is a little confusing, but most people seem to have the later, three post relay. Especially for 16.95! Russ Farris