Tachometer wire routing tips please

[livingskies]

Want to hook up a Bosch tach on the '74 bay window bus. Three of the wires (positive, negative, and light) can likely be connected under the dash. But the green wire has to run to the coil.

Any tips for the a good but easy place to run that wire from the dash to the coil? Not seeing any good options after looking at it for a while. Thanks for any help.

[mikedjames]

Get a multicore cable, reasonably heavy duty, run it alongside the wiring harness duct from the rear of the bus to the front of the bus. Use one core for the feed from the coil, may need a diode in the cable to make it work.
Something like trailer light board wiring.

Then if you want to run other electrical circuits, use another spare core of the wire.
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[CanStan]

I have an early Bay, but hopefully you can do something similar.
I used a length of bulk cord from an auto parts place. It looks like (and maybe is) extension cord with 3 wires inside, with a nice thick insulation covering it. I think I got them to cut maybe a 20’ lenghth or so off the bulk roll. If you lay under the bus, you should be able to see a nice logical path to route it. I used a bunch of the factory holes in the cross members and it was easy to get from front to back. A couple zip ties, and it wasn’t going anywhere. Just watch that it’s out of the way around the axles. At the back I got it into the engine bay where the main harness enters on the fire wall. Up front, I was able to fish it up the nose through some existing holes as well. I think maybe where the speedo cable went up? I pushed it right up to the fuse panel area from there. It only took 20 mins tops to run it.
I like the 3 wire cord for 2 reasons. One, because of the heavy duty waterproof sheathing, and two, if I ever decide to run a temp gauge or whatever else, the wires are already there.

[livingskies]

Thanks to both of the posters above. Excellent idea to use a multi-strand cord with an extra layer of protective covering.

[BUSBOSS]

Look for bundled trailer wire. 14AWG is a nice size considering the length of the run and remember to hook up your chosen wire color to the negative side of your coil. Here is a picture of the 6 wire version which will leave you with plenty of future options.

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1970 Karmann Ghia Convertible (sold - but not forgotten)

[KentABQ]

Not sure if this works on all years of van/buses...
But I ran about a 12' length of 1/2" PEX from below the right side of the engine bay to near the steering column, and then ran my wiring thru there. There were existing openings thru the beams that made it easy to route securely. This acts as a good flexible conduit to run the wiring from back to front. (I would suggest only running signal wiring thru there and no power feeds that may screw up the signal. )
Then both ends of the PEX were sealed with heat shrink tubing where the wires come out.

It gives me peace o' mind that the wiring is protected.

Oh, I also ran the CHT thermocoupling wiring thru the PEX.
BUT make sure the wiring is routed thru the right way, since the wires have to be hooked up correctly.
If not, you'll be pulling the wiring out and redoing everything again... as I had to do.
Lesson learned.

[brownbus2]

I did what Kent did for my CHT and oil temp ...
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1976 FI Marino Yellow Westy

[aeromech]

I’ve done it many times. Start at your dash and leave extra length. Go down behind the kick panels til you’re by the drivers feet. You’ll find an existing wire conduit there. You need to remove the pedal splash pan. Go under and fish your wire down alongside the conduit and tie wrap. From there follow the conduit to the passenger side and aft. It gets tricky going around the front beam but it you have patience you can fish your wire through the structure. The conduit ends about where your starter is. From there just fish the wire alongside your battery to starter cable and secure.
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[alman72]

there is no wire in the diagnostic plug that goes all the way up front, is there?

[jtauxe]

[jamesdagg]