Engine swapped- What do these connectors go to?

[redrocket328]

Hey guys, So im building a spece30 car and my chassis is a '87 325is. I purchased a '89 donor car for a couple parts and the new motor that was in it. I swapped the complete engine with tranny attached and wiring harness. After a bunch of other things, the car fired right up on the first try but I dont know what these connectors go to, or how to rewire them. The come right out of the ECU. The old '87 harness is a bit different and doesnt have these same connectors. Although the engine does run, a couple things dont work, like my RPM guage.

What do these connectors go to?
Are they important to rewire or should i leave them unplugged?
Any impact on why my RPM guage isnt working?

[jlevie]

You don't need those on a race car, but the reason the tach (and econometer) isn't working is because this later harness is missing the three pin white connector found on the original harness. Later cars route the START, tach, and econometer signals via C101. Yor 87 routes those via the three wire connector pigtailed off the engine harness. The easy fix for this it to swap in the engine harness from your 87.

[redrocket328]

Thanks Jim. I don't think it will be worth it to swap engine harnesses personally. I was thinking about putting after marking gauges in anyway, in place of the cluster. RPM, water temp, oil temp and pressure and batt volt. In that case, if i end up doing that , I should just leave these connectors unplugged correct?

Any idea how to harness in an aftermarket RPM gauge?

[call me jack]

isn't that c101 issue just a quick wire splicing? would be a lot easier that reinstalling the old harness.

[jlevie]

I don't think the body side of C101 has a pin for the tach and econometer signals, so it is a bit more than just a wire splice. But you can splice in the three wire connector from the early harness near the DME connector.

If you replace the cluster with aftermarket gages you should include warning lights for the CEL, ABS, and Alternator. The last (or an equivalent resistor) is necessary for the alternator to charge.

In my opinion, the best aftermarket replacement for the cluster is a RacePak IQ3 or better (AIM or Stack). You get the gages you need, GPS data logging, shift lights, and "smart" warning lights for critical items (like oil pressure, coolant temp, etc).

[redrocket328]

isn't that c101 issue just a quick wire splicing? would be a lot easier that reinstalling the old harness.

Yes, I believe that is C101 because the engine harness is from a '89. But the body electrical harness is from the '87 is it is not C101.

I am wondering if there is a way to splice them together somehow to work with each other.

[jlevie]

Your 87 cluster is fed the tach and econometer signals via the three wire pigtail off the engine harness. There is no wiring in the car for those to C101. To regain the use of the tach you'd have to add pins to C101 and route the wires to there, or cannibalize the connector from your 87 harness and splice it into the 89 harness, or swap to the 87 harness. That is all the options there are.

[redrocket328]

Your 87 cluster is fed the tach and econometer signals via the three wire pigtail off the engine harness. There is no wiring in the car for those to C101. To regain the use of the tach you'd have to add pins to C101 and route the wires to there, or cannibalize the connector from your 87 harness and splice it into the 89 harness, or swap to the 87 harness. That is all the options there are.

Thanks again Jim. I think I understand better now. Does the Tach gain signal from the coil itself or the crankshaft speed sensor? Can I tap into one of those wires off the sensor and run it into the black/blue wire that comes from the 3 pin connector on the 87 body harness? I know the crankshaft speed sensor has a black and a yellow/black wire. Shall I tap into one of them?

[jlevie]

The tach signal is generated within the DME based on data from the CPS. While some aftermarket tachometers can use the sigal from the coil, the one in the cluster must use the one generated by the DME. The wire to tap into is the one connected to pin 6 of the DME connected. I sort of think it is a black wire, but I'm not sure. The way to identify the tach wire is to open up the DME connector, identify pin 6 and tap into that wire.

[TStroop]

So what do those two plugs go to I was wondering the same. Currently swapping my 87e with a 88i.