Bad ECU or something more...?

[LaMamelle]

Howdy! I just got my hands on a new (to me, not to the world) 1986 XT Turbo, that's been sitting in the previous owner's driveway since at least 2009. It has less than 100k miles, no accident history, and very little rust, or at least, not enough rust to make any holes. The reason it was sitting was because the ECU was fried. To what extent I do not know, all I know that he plugged in a wire and then realized it shouldn't be there, and there was no power. It looks like there is a fair bit of custom wiring that I am still in the process of investigating. I was able to get my hands on a replacement ECU, and I'm just waiting for it to arrive. However, there are some things that make me wonder if the issue could be deeper. There are some electrical systems work, but others that don't that I would expect to work. For example, brake lights and highlights work, but not the hazards, or turn signals. And I expected the radio and digi-dash to at least come up with light, but there's nothing. Looking at some wiring diagrams I think (If I'm reading it right) some of these systems should work without the ECU, but I could be wrong? I already plan to replace all the relays I can reach, and check every fuse, I assume that's a good place to start. Does anyone have any suggestions for where I should look out for? Thanks in advance!

[LaMamelle]

Just a quick update to this: I have gotten hazards to come back to life just by flipping the twitch about a million times, slowly beginning to wonder if the issue lies somewhere other than the ECU. The 1988 manual says that most body electronics go through the fusible links and ignition. I've double checked the links and they are all clean and they don't seem to be damaged in any way. So I'll try to diagnose the ignition switch next.

[LaMamelle]

Update: There didn't seem to be any voltage at the ignition switch, so I switched it out with the one on my 89 XT, and I now have radio! But no still no dash lights :(. But this does seem to lead me down the path that the issue may lie elsewhere, and not at the ECU. If anyone knows to what extent the dash would communicate with the ECU (or the MPFI Controller as the manual calls it), lemme know. But I'll keep digging. I hope that one day I will see that magnificent digi-dash.

[el_freddo]

I don’t think the EA82 era ECUs were integrated into the dash anymore than having a check engine light and referencing a reed switch on the speedo cable for the VSS. 

Do some research into issues with the digi dash, the EA81 MY’s digi dash was known for issues with some of the components dying, taking out the dash with it. You could have a similar issue in the EA82 digi dash. 

Cheers 

Bennie

[LaMamelle]

Thanks for the tip, I'll take out the dash and check it out. Something I should probably do anyways; I don't put a lot of faith in 80s circuitry. And I think that confirms for me that the issue is the ignition switch. I'll replace it and update on my success for failure.

[SuspiciousPizza]

I'd investigate your relays for your lighting issues. Getting stuff to work after repeatedly flipping the switch sounds to me like a relay issue.

Look into service manuals online, or better yet buy a set of hardcopies. Well worth the investment and will tell you all you want to know and more.

I believe the wiring should be the same as any 3rd gen/L-Series/Leone with a turbo MPFI engine. An XT is basically an L-Series with a cooler body and interior. I could be wrong though, I've never been fortunate enough to work on one nor see one in the flesh.

Check everything that goes into the ECU before you plug it in. Takes time but with the car's age it's better to begin checking stuff now. 

:]