Hey guys how ya doing ? I got a 1988 FC convertible (s4) i bought it with a blown rear rotor and i replaced the engine with a used engine. So long story short we put the majority of things together ( enough for it to at least turn over ) and when we dropped the battery in only the brake lights, e brake dash light, low coolant buzzer and door lights worked. Stupid us we forgot to put the ecu back in the car. So we put it in. That changed nothing. That ecu did get left in the rain tho so moving on. I bought 2 known workinh ecus. Put one in heard the fuel pump come on and i think the fuel injectors. Thats the only thing the car did different. Everything else is still dead. Dash lights, headlights, I'm at a loss guys. Im bad with electric problems so i could really use the help (yes i checked fuses i might have missed one tho)

 

there's a small Positive black wire that goes to the main engine bay fuse block.
It has a single clip.
That feeds the fuse block.The other thicker wire will go to the alternator(so it's on that piece of harness that you would look for this one small wire).
It's often overlooked when hooking up stuff,so check that out.

 

Does the alternator have to be hooked up for the car to turnover? And I'll check that wire

 

You don't necessarily need to have the 2 wire connector on it,but the main wire to the alt (B+) is nice to have hooked up!.
Without the alt in the system the battery won't recharge so as soon as battery power gets sucked out the car would die.Even if the car starts as soon as the voltage drops the Ecu would say "hey..where the Fark is my 12 volts!"..and conk out..(car would shut down)
I "think" The harness would feed the Starter from battery.Another harness feeds the Alt to the battery and the Fuse block.
Been a while fartin' with wires.

 

I'll hook the alternator up and check that wire when i get a chance. I'll let you know what happens. Thanks for the info!

 

The interior and hazard lights are powered by the BTN fuse in the engine fuse box. The wire coming from the fuse to the interior fuse box is White/Red. The wire powers the illumination, stop, room, antenna, hazard, heater and defroster fuses. If any of these fuses were pulled there would be constant voltage on one side of the fuse slot.

The head fuse in the engine fuse box powers the headlights. The headlight switch just places a ground to the headlight relay to turn the lights on (turns them on but doesn't pop them up). The White/Blue wire at the headlight relay when grounded will turn the lights on. Ground this wire via jumper wire and the lights should turn on (not pop up).

W/key to on the Brown/White wire at the TPS, boost sensor should have 5 volts. This will tell you if the ECU is powered on.

 

Okay i checked those wires on the fuse block and they're hooked up. I also hooked the alternator up. Same results. Fuel pump comes on, injectors click, and thats all. The low coolant buzzer eventually comes on too.

 

Ok quick update. It acts the same whether the ecu is plugged in or not. The ecu just has 3 plugs right? And does it need to be bolted down?

 

No, the ECU does not need to be bolted down. Does the W/R wire at the engine fuse box have constant power or not. If it does then does the Red wires at the headlight relay have constant voltage or not? If it does did you ground the Blue/White wire as suggested to see if it caused the headlights to turn on?

 

When is the fuel pump turning on? It should not turn on w/just key to on but more like w/key to start. You also stated the car acts the same w/the ECU plugged in or not. The ECU controls the injectors so they should not be clicking unless something is really screwed up.

Does the starter engage w/key to start?

 

The fuel pump turns on with the key to on. And it doesnt shut off. Something clicks when i turn it to on but I'm not sure what. No the starter doesn't engage when the key is turned to start. I have 3 different ecus. It acts the same with all of them. It acts the same if it doesnt have one at all. The car is an electrical mess

 

The pump will turn on w/key to on and engine off only if the fuel check connector is jumpered or the AFM door is stuck open otherwise it should not be doing what it is doing.

The ECU does not control the headlights, starter engaging or the fuel pump turning on.

You can tell if the ignition switch is powered w/constant voltage if the turn signals or wipers work w/key to on. I'm going to guess they do not then you need to see why the switch is not powered. Styx asked you to check the cable going from the battery to the engine fuse box. You said it was intact. On the opposite side of the fuse box is a larger cable powered by the Main fuse. The cable drops downward below the fuse box by about a foot and plugs into a connector w/a like cable. This cable makes its way to the ignition switch to power it w/constant voltage. At the switch will be a plug with a Black/White wire and a solid Black wire. The Black wire is the wire powered by the Main fuse that powers the ignition switch thus it should have constant voltage. Now find if the ignition switch has constant power and if not then find out why based on the info provided.