1985 Renkin with 1982 Mercruiser 470 engine harness - instrumentation wiring help

Blueghost924

Petty Officer 1st Class
Joined
Sep 19, 2013
Messages
250
I bought a 1985 Renkin that has a 1982 Mercruiser 470 with the typical round plug engine wiring (9 pin I believe). It runs through the boat and up to the center console, where it plugs into the instrumentation harness via an 8 pin rectangular connector (although there's only 7 wires). BTW - in looking at the wiring inside the console, it's somewhat of a mess. I'm facing a couple of problems:

1. The key ignition switch has been completed disconnected. I've looked at several wiring diagrams from the Mercruiser manuals I've downloaded, and I'm just not quite sure which color wires goes to the 3 connections on the ignition switch (and where the wires come from). A couple of diagrams mention a red/yellow wire, but I don't see a red/yellow wire, just a yellow. How do I wire this?

2. The large 10 gauge red wire on the rectangular plug has been cut by the previous owner right at the base. Looks like the other end is hanging from a 10 gauge red wire connected to a long terminal strip. Does this make sense as to where it should be re-connected at?

I've traced the 7 wires on the plug, and here's the order and where they appear to go from left to right on one side:

Tan - Temp Gauge
Blue - Oil Gauge
Purple - Oil and Temp Gauges
Red - ?? (appears to connect up to terminal strip) (10 gauge)

On the other side left to right:

Black - Oil Gauge (10 gauge)
Grey - Tachometer
Yellow - not connected, just hanging free

To figure out this mess, I've looked online for Mercruiser instrumentation wire harness. On Basic Power Industries' website, they have a MAR 6108 part number that seems to match up with what I have. Is there another or better source of a new instrumentation wire harness?

Help! :confused:
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
The back of the ignition switch should have letters "B" (battery - +12 volts) from the engine. "I" (ignition - +12 volts back to the ignition system) when the key is in the RUN position. "S" (start - 12 volts going to the starter solenoid on the engine). All of the gauges require +12 volts and ground. Therefore, the "I" terminal on the ignition switch feeds the "I" terminal on all of the gauges. Just daisy chain these terminals from one to the next. Ground on each gauge is also daisy chained to the ground connection at the console (wherever you find it -- but should be a black wire in the engine harness. Every gauge except the voltmeter (if you have one) and the speedometer requires a sender "S" connection. Fuel sender in the tank feeds the "S" on the fuel gauge. Tach (gray wire) goes to the "S" terminal on the tach. "S" on the oil pressure gauge comes from the oil pressure sender on the engine. The "S" terminal on the Temperature gauge connects to the temperature sender on the engine. If you have a speedometer, the tube from the pitot on the engine lower unit or the pitot on the stern connects to the back of the speedometer. All of the gauges typically have an internal light. That connection is via the NAV side of the NAV/ANC light switch. Since the wiring at the console has been butchered, I can't tell you with any certainty what goes where. Your eyes are needed for this. Look at the loose wires at the console and then look at the engine end of the harness to see where each wire goes. Best to obtain a service manual for your specific engine/drive.
 

Blueghost924

Petty Officer 1st Class
Joined
Sep 19, 2013
Messages
250
Thanks SIlver, and following each line is exactly what I'm going to have to do. I need to see if the 9 pin main wire that goes from the engine through the boat to the console is working as well!
 
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