FD3SEngineering

iTrader: (4)

I have been working on a friends wife's 1991 Convertible and I have come across something I have never seen before. The car kept loosing electrical power, cleaning the terminals and replacing the alternator (which was less then 1yr old) helped for some time. Finally it died and was towed to me. I get power at the engine bay fuse block, all the fuses test out fine, and there is no electrical smell/ect. When we tried another battery, I got a faint beep and a quick flash of lights, then nothing after connecting the terminals.

After checking the charge harness/engine wiring as best I could, I moved to the cabin fuse block. Here I have absolutely no power. Same goes for the ignition wires. I moved back to the engine bay for a few minutes with my test probe, and here is where it got strange. I had my 12v test light connected to the Negative battery terminal and while testing various wires, I slipped and touched a bare metal bracket that was bolted to the strut tower. My light lit up. From any ground point on the car to the negative battery terminal, I have 12v power...

All that I can think of is a short, but no fuses are blown?
Hailers?

misterstyx69

iTrader: (142)

Did you have your Positive lead hooked up to the battery when using the Test light?
if you did,your light would create a Closed circuit and light up when touching any ground.

HAILERS2

Look at the attached jpg of the interior fuse box

The fuses in Red are the battery bus and should have power 24/7 and are fed from the BTN fuse in the engine bay. They are not related to the runing of the engine at all.

The fuses below colored in green are only powered by the key being ON. No key to ON then no power there. You need the fuses on the row with the ENGINE fuse to be powered up for the engine to run at all.

If the key is to ON and the fuses in green don't have power..........then the ignition switch isn't feeding them.

The ignition switch has ?? four elect plugs. One plug has two wires one of which is Black and the other Black/White. The BLACK wire should have power 24/7 or things won't ever work.

That Black wire comes from the engine bay fuse box. There is but one connector b/t the engine bay fuse box and the igniton switch. That connector has a single black wire and is locted about six inches below and inboard of the engine bay fuse box. Make sure that connector has power and is coupled together good.

IF the black wire has power......................and when the key is to ON the fuses in the interior fuse box don't have power............then pull that connector apart and with a piece of wire couple the Black wire to the Black/White wire. Now the fuses on the row with the ENGINE fuse should be powered and the engine should start. Fuses on the row below Engine won't have power doing this.

HAILERS2

IF you had no power anywhere on the interior fuse box..............shoulda. The Batt bus gets fed by the BTN fuse in the engine bay. See if that fuse is good.

Engine bay fuse box is fed by a cable connected to the FRONT of that fuse box and that cable is held on the fuse box with a 10mm wrench size bolt. Comes from the batterys positive post. So make sure power is on that cable.

Make sure the wire connectors on the Bottom of that fuse box are on snug.

On the aft side of the engine bay fuse box is a cable bolted on that fuse box. Its held on with a 10mm wrench size bolt under a plastic flap. make sure that cable has batt voltge

I understand there is no power to anything at all. The headlights/side lights don't work? Stop lights don't work? IF they do, then the interior fuse box is getting power on its battery bus. IF no lights work then the problem lies with the engine bay fuse boxes BTN fuse not getting power to it. Or that fuse being bad. Even if that fuse was bad and the interior fuse boxes batt bus does not get fed...........the engine would still run and you'd just lose lighting or things on the interior fuse boxes batt bus.

A lack of power from the ignition switch would not cause side lights/stop lights from working. So if those lights don't have power most likely the problem is not with the ignition switch but lies in the engine bay fuse box not getting power to it.

FD3SEngineering

iTrader: (4)

No power to ANYTHING. No lights, no cranking, nothing. BTN fuse is good. Wires are all correct, the engine bay fuse block has power 100%. Tested the chassis harness side of where the wires connect to the fuse block and all (including BTN) have power. There is a short between the engine fuse block and the cabin fuse block. I will take a look at it again in the morning. Thanks Hailers!

HAILERS2

Odd. Because there are no other connectors b/t the Engine bay fuse box's BTN fuse and the interior fuse box. See the attached jpg.

The wires leave the engine bay fuse box in the engine harness and end up at the interior fuse box in the same engine harness.

Should be a WHITE/RED wire leaving the engine bay fuse box (below the BTN fuse) and arriving at the interior fuse box as the same WHITE/RED wire.

Sorry world, I've never taken a interior fuse box out of a RX and don't plan to. Looks like way too much work. I'm not sure how the White/Red attaches to the interior fuse box.

HAILERS2

Actually this is strange to me. The reason I say that is.................when you want to turn the headlights on all you do when turning the headlight switch to ON, is your putting a ground on the headlight relay. You need no power at the headlight switch to do this.

The headlight relay is next to the radiator and has power coming to it from the HEADLIGHT fuse in the engine bay all the time. It's just waiting for the ground signal from the headlight switch to pull the relay in and make the headlights come on. Headlight assy don't come up but the headlights should come on. Again, no power needed at the headlight switch.

Which makes me think a bit. Something on the order of no power is actually at the interior fuse box. You may get a test light to light up but when a item is causing a large draw of power ..........it ain't thar no mo. Something to do with a bad battery internally or bad connection at the battery posts or bad connection at the engine bay fuse box coming from the battery.

Test lights don't draw squat in power/current and may light up but anything else that requires any current at all may not work/come on.

Swap a battery out of some other car temp.

Or since I do screwy things in life............pull the WHITE/RED wire off the bottom of the engine bay fuse box. Get a piece of elect wire bare at each end. Somehow connect that new wire to the White/Red wire you just pulled off and the other end of that new wire touch the positive cable/post of the battery with the headlight switch to ON. Side lights on the car should come on and the tail lights should come on. Headlights probably won't come on.

This way your bypassing the engine bay fuse box and the cable b/t it and the battery and if the battery is worth a darn the side lights (running lights?) should come on. And if they do come on................means the power from the batt is not getting to the engine bay fuse box in any meaningful manner. IF the running lights dont come on then I'd suspect the battery and swap in another batt.

I ASSUME the battery negative cable is grounded. It grounds on the long starter attach bolt or sometimes on one of the bolts that hold the transmisison to the engine..........plus it branches off and also grounds at the bottom of the left strut towers sheetmetal.

I've never done the above but I know it should work like I say it should.