M25 Engine Wiring Upgrade Part 1--Cockpit Gauges
by, 02-07-2014 at 02:27 PM (8504 Views)
Well, twice last year my M25 diesel wouldn't start up again after being turned off. I could jump the solenoid with a screwdriver--if there was someone in the cockpit to hold down the paired glow plug and starter buttons. When it happened singlehanded I had to sail into the slip, picking my way through maniacal 10-year-old Optimist pram racers all yelling "Starboard!" at me like Transpac lawyers. So, there was that.
And then there were the gauges. The tachometer jumped like a kangaroo. The ammeter didn't function at all, which was good, since maybe it was disconnected and that wiring upgrade had already been done. The faded water temperature dial never got above 160. But was it measuring anything? The switch to test the oil light was quite mysterious, and eventually understood only after abandoning Aristotelian deductive logic, which, although it sustained Christianity for a Millennium, is quite susceptible to the false premise eventually identified for me by Tom Metzger. Under the back cover of the panel gauges was the usual tangle of wiring. It looked OK from a bar stool at midnight, but upon sober inspection in the morning had a rode-hard-and-put-away-wet appearance. So I determined to fix the old girl up with two bucks and a pat on the head. This was, as usual, an underestimation.
Aging marine electrical systems wear down but not out. Renewing them is mostly just a matter of performing well-known safety upgrades, re-terminating wires, improving grounds and changing instruments and switches that are worn out. The necessary procedures are all explained in the links below. A few quick scans will make it all clear for anyone of average intelligence who has worked on the Space Shuttle or dug a root cellar in permafrost. I personally did it all without really understanding any of it, which remains a source of great personal satisfaction.
It was some time since attention had been paid to the back side of my cockpit instruments. Several ring terminals were hanging by a thread. The ammeter lamp had corroded right off. The push-pull ignition switch and the buttons for glow and start were suspect, and with no lock washers the terminal screws were perpetually loose. An in-line fuse holder, when opened, crumbled to rusty dust. Most panel wires arrived through an 8-pin connector hidden out of sight under the cockpit floor. There are two of these famous "trailer connectors", the other one being in the engine compartment. They allowed the installation crew in Irvine back in 1985 to just snap the electrical system together. But over the years corrosion may have introduced unwanted resistance, so time to cut them out. In fact, I concluded that I might as well replace everything. Here's what I ordered from Defender:
#300511 TEL HDS DIESEL TACH
#303996 TEL WATER TEMP AMEGA
# 03943 TEL VOLTMETER 8-18 VDC AMEGA
COLE OFF-ON PUSH PULL SWITCH
COLE PUSH BUTTON SWITCH (Off/Momentary On) (2)
The Teleflex Amega line of tachometer, voltmeter and water temperature gauge matched exactly my originals, so they went right in. None of the senders needed to be replaced, and the original wiring was fine. In the photo below you can see the cut-off trailer connectors. I just joined the ends with heat-seal butt connectors, being sure to leave enough wire so that the panel could be removed from the bulkhead. I re-terminated all the wires with new ring connectors, polished up the contacts, and disposed of many old wires that went nowhere.
The voltmeter was introduced as part of Ammeter Replacement .
The new start and glow-plug buttons and push-pull ignition switch were mostly for bright and shiny peace of mind. I even bought a new oil light test switch, since the old one didn't seem to do anything. Sometimes it lit up the oil light and sometimes it didn't. I tried it with the engine on and the engine off. When faced with a puzzle like this, what I do is logically think it through. I envision the purpose of an electrical component, trace its circuitry in the mind's eye, and apply logic. That way you avoid the dumb mistakes of inexperienced boobs. For example, the salesman at West Marine, who when I explained the oil light test circuitry to him didn't seem to really grasp it. He did sell me an expensive switch. However, when I removed the old one, its wires were not connected to anything. I effortlessly deduced that this could well be the cause of its intermittent function. But without a wiring pattern to copy, I didn't know how to wire it. Furthermore, the oil light test switch was not on any Ericson wiring diagram I could find. So, taking advantage of the Ericson Forum, I asked Tom Metzger for help.
"Oil light test switch?" he said. "What is that? No such thing."
"Yes, there is. Look at the picture I sent. It's the switch right under the damned oil light."
"That's the blower switch. It's not on the schematic because the blower was optional. Do you have a blower?"
"Of course not. I threw it away last year. Who needs a blower with a diesel?"
"Well, you still have the switch." I could hear Metzger laughing while typing a thousand miles away. "Since it has nothing to do with the oil light, you can throw it away too."
But look how nice it all came out. On the left, the battered old unreliable instrument panel with "oil light test switch". On the right, the shiny new one. A tach that doesn't bounce, buttons that that feel secure, wires with guaranteed connections, all good for thirty more years. And I did it all with my pretty little hands.
However, when I pulled the new ignition switch for the first time the engine started. This surprise threw me back three feet. When you pull that switch the lift pump starts, the oil light comes on, the gauges activate. The engine is not supposed to roar to life like carnival in Brazil..
Panic email to Metzger: Now what have I done?
He got back in an hour. Those shiny new buttons you bought for glow plug and starter--does the box say Normal Off, Mom on? Mom is for "momentary". Because if they say Normal On, Momentary off, you bought the wrong ones. Just change them. There being no emoticon for "What an Idiot", he closed with a Smiley Face.
So I changed the buttons and now I have a new cockpit panel which looks really, really good and an engine that starts right up.
Next: Engine Wiring Upgrade Part 2--Alternator Jump and Ground Bus