What it took to get reverse lights...

[Gojira94]

Let me preface this with an apology for being long-winded...

 

My 1987 rig started out as a base 2WD, AX4, 2.5l. POs were in the beginning stages of 'making one good out of two' MJs. The engine harness MAY be original. The engine control harness is definitely from 89 or 90, no C101. The 1990 FSM shows C115 being the only thing on the tree besides the ECU connectors on the inside portion of the engine control harness. I strongly believe my instrument panel harness is original, 1987. Emissions maintenance timer wasn't in the electrical manuals until 1988, and mine has no provision for it.

 

Now... C115. I have a theory, maybe some of you can confirm or correct- the type/ shape of connector C115 may have changed in 1989 or 1990. On top of that, if the engine control harness was for a manual, along with not having C113, two of the pins present in C115 for an automatic might be absent in a harness for a manual. Leaving just one wire- pin H, BLK/YEL. I'd have to see an unmolested auto MJ or XJ to confirm.

 

So... I had no reverse lights. They're dependent on switched 12V in run/ start. Confirmed 12V power at the TRANS fuse socket, brown wire coming in through C100 pin C5 by touching a ground point with the negative lead of my meter. What I believed to be C115 on the IP harness side has continuity from the other side of the TRANS fuse socket on the BLK/YEL wire on pin H. That side of the fuse has another BLK/YEL wire going to "transmission controls." Pin K on C115, BLU W/TR goes to pin A on C260, cruise/ trans switch.

 

Anyway, I tested continuity from C111, pin A, BLK/YEL to the lone pin populated in the engine control harness side of C115. There we go, confirmed. Next I took a leap and jumpered the BLK/YEL wire on these 2 very different looking connectors and tested. Et voila, reverse lights now work.

 

 

 

Is there something I've missed here? I mean I can live with this, make it solid and neat and tucked out of sight forever, but surely... I must be missing something a little more obvious?

 

[eaglescout526]

I have never ever seen either of those two be involved with the reverse lamps. I know power goes to the switch, to the trans fuse and out to the lamps. As to what connectors, I am not sure but that can’t be right with what you have. 

[Ωhm]

1 hour ago, Gojira94 said:

Now... C115. I have a theory, maybe some of you can confirm or correct- the type/ shape of connector C115 may have changed in 1989 or 1990.

 

Is it possible that you have two (2) C115's?

[Gojira94]

34 minutes ago, Ωhm said:

Is it possible that you have two (2) C115's?

 

Well, one side in my pic above (larger connector with 3 wires) is attached to the instrument panel harness and shares a wire with the cruise power-cancel/ TCC unlock connector (also visible in pic above). The other side (small connector, upper right, one wire) is attached to the engine control harness. So I don't think so. I suspect I might have mismatched, by year and harness types, connectors for the 2 sides of C115.

 

I took some pics under the dash of an 89 auto XJ when I was pulling my column and cruise parts from it. I'll have a look at those and see if I'm lucky enough to have captured anything relevant to this question.

[Gojira94]

Pics on the 89 auto XJ don't show anything. I was focused on cruise parts and connections. What I can say for sure is that C111 (manual only) pin A for a 4L goes straight to pin H on C115. C111 pin B is power and passes through C100 C5 to the hot side of the trans fuse. What apparently is C115 (engine control harness side) on mine I'd ignored, thinking it was the emissions maintenance timer connector until I looked closer at the 87 and 88 electrical manuals and noticed 87 didn't have one. And the color of that BLK/YEL wire taunting me lol. Polarity of the reverse switch on the trans itself makes no difference, obviously.

 

This is from the 87 manual, 88 is identical. Though 87 shows diesel-optioned connections.

 

 

[Ωhm]

That small connector in the first photo (circled), is that a 2 pin?

[Gojira94]

1 hour ago, Ωhm said:

That small connector in the first photo (circled), is that a 2 pin?

3 cavity connector.