Tonight I did a little looking around at my tach situation. I found the pickup in place on the engine with the wire clipped. The tach-amp has about 6 inches of wire sticking on its side. Sadly the wires arnt't long enough to reconnect. Any idea on what kind of cable to replace it with? I have some #16-TSP that we use at work for 4-20ma signals, I was thinking about that.



There is a loom of wire coming out of the tach-amp holder and going into a loom headed to the fire wall. the other part of that loom, not going to the tach amp holder is a mess of wire. It looks like this is where the glow plug relay should be wired up. But since the car started life as a 280E I assume these wires were cut as part of the conversion to diesel.



These are the wires under the tach amp. One of the wires is tied to the harness going to the new GP relay. Its located near the battery. It looks like the GP relay for a 116 SD (dang didn't grab a picture of that) Here are the wires.



If you fallow the red wire that is extended under the tach-amp back tward the fire wall it joins some other wires in a loom. A green wire is coming from the firewall and 2 others are coming from anothe harness at the firewall. These 4 wires go into that loom and over to the GP relay.



I haven't looked into any of this wiring yet. But I'm hoping to figure it out. This car has some intresting wiring thanks to its past. Did the 280 engine use the same kind of tachamp base? maybe as a place for a diognostic tool? I know on gas cars the distributor gives the RPM signal, but did it use the same tach amp? Or maybe the person who swapped the engines added it? maybe he swapped the whole harness, and thats why there are wires under the tach amp (for the GP relay?) But that doesn't explain why it has the other style GP relay... This is a mystery!

If the admins would like to rename this thread, I think I'm just scratching the surface of the mysteries that is the wiring in this car. I found these wires going to the engine by the alternator.



The black/red wire continuse around the head to the temp sensor.


You can also see in this pictuer that the GPs are linked together. They are all linked together and then one wire goes the GP relay through a 50A strip fuse. It was getting power directly from the + post on the battery.

I bought a new strip fuse holder as the one in the car was melted, the fues is good and the GPs work, maybe an old fuse blew out in the holder. I'm going to replace it. I was thinking of fusing the it up pstream of the relay. Any idea why the swapper fused it after the relay?

I'll take some more pics tomorrow.

What is funny is everything in the car appears to work, so the fellow tho did this wireing did it right, well, enough to get the car to work. I'd just like to clean it up and get a tach in the car. Its got the huge clock... but the wiring seems to lead me to believe maybe the car once had a tach. maybe the guy didn't have a tach so he swapped in a clock? Mysteries!!!

Thanks for reading all about my mystery wiring. Feel free to chime in with any clues!

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