91 Blazer issues, brake light switch

[85 Jimmy]

Ok, so first off I just swapped bodys from a rusted out 85 jimmy to a pretty clean, never been offroad 91 blazer body. I just got the front clip back on it and was checking threw everything, I'll list off a few of the problems right now.

To be clear, I'm running TPI with a stand alone harness and computer and I still have the old harness in the truck but it's not hooked up to the old ECM, and the only things on that harness that are hooked up are the alternator and the A/C compressor.

I haven't checked any fuses or anything, I just got it back together and it got dark, so I didn't feel like fumbling around in the dark.

The headlights don't work, but the turn signals work.
The power windows and locks don't work.
The wiper motor doesn't come on.
The alternator isn't charging (probably just a bad alt).
The back glass goes down, but not up. I had to take the cover off and use my drill to get the glass back up.
The brake lights stay on. I'm running hydroboost and thought I just had to adjust the switch, but they still stay on.

Is there a connection for most of that that I might have overlooked?
I might just go out and start looking at the fuses, but it'd help if someone could please post up a complete wiring diagram for the truck.

This is where I'm at with it right now, just to be a pic whore

 

[85 Jimmy]

I just checked the fuses, the ONLY fuse that has power to it is the brake/hazard fuse. I pushed in the hazard button on the column and the light in the floor shifter for the t-case came on and the buzzer came on.
So I plugged in the old ECM and a white connector with maybe 6 wires in it and a black connector with 2 wires in each side. I went and turned the hazards back on and the stuff that happened before didn't happen, but the hazard lights came on and stayed on, (I think they weren't flashing b/c of the brake lights.
I even checked the fuses with the key on with the engine running and not running and the brake/hazard was still the only one that has power.

I know for a fact that yesterday the blower motor would turn on, but today it won't. Also I have autometer gauges and I pulled power from the aux spot on the fuse block, and all my gauges work with the key on and with the engine running...

Also, the grounds in the engine harness are grounded out to the block, the the grounds in the front light harness are not hooked up yet.

Sorry about being all over the place

 

[Fordum]

I don't have the best schematics for that year. For some reason, all I have is for an RV chassis, but most of it should be the same.

First thing, go ahead and make sure all the grounds are hooked up. Not only will that probably get your headlights working, but some of the stuff that is working might be getting its ground through other equipment that should not see that load

Next, if you were able to plug in the rear light harness, then hopefully it should be fine.
If you had to splice it, be warned that some of the wires change color at the plug.

You said the turn signals were working, but it uses the brake lights for turn signals, so if they are stuck on, do they blink when they are supposed to?

Hope these schematics help.

I had to ZIP them because they are too big as PDF

 

[85 Jimmy]

The rear doesn't blink, only the front, and only when the rear harness is unplugged. If the rear harness is plugged in the front blinkers do not blink, and with the hazards on the front and back do not blink regardless if the rear harness is plugged in or not.

Everything electrical on the truck but the TPI system is off the 91 blazer. When I swapped bodies I just unplugged everything, drapped the harness out of the way, and rolled the frame out from under the body. I did the same with the 85 that I already swapped one tons and Tuned port into and rolled that frame under the 91 body.

I'll look over those schematics and go over everything again tomorrow during the daylight. Hopefully it's just a fuse that ties everything together. Yesterday or the day before I know atleast the blower motor would turn on, then I put the front clip on today and it doesn't come on...

 

[Fordum]

Try running a ground wire from the battery to the fan motor temporarily. If it runs, then you still are missing a ground and need to find it and hook it up before you do much more.

Also, unhook the brake light switch and see if the lights go out. If they don't, then you have power feeding from somewhere it shouldn't.

Also, make sure that you have both flasher modules. The hazard is a different one from the turn signals.
Most hazards will not blink if the brake light switch is on. Also, the brake lights run through the turn signals.

It sounds like you have either a missing ground or two, or something miswired. I'll run down and post some earlier schematics that show how the turn signal switch works.

 

[Fordum]

These might help.
I went with an 87 just for nostalgia's sake.

 

[y5mgisi]

All i can think of is that looks exactly like ColbyStephens' Blazer!

 

[85 Jimmy]

Thanks alot, I'll see what I come up with tomorrow.

 

[85 Jimmy]

All i can think of is that looks exactly like ColbyStephens' Blazer!

Yea, I saw his and thought to myself "I have one just like that". His looks like it has a straighter body and nicer paint though. Hopefully after I get everything working I can wash it and see what a coat of wax will do.

 

[85 Jimmy]

So I looked over the diagrams and then went put and stared at the harness from the 85, then went and looked at the chassis for the 91, and found that on the 91 there was a cable straight from the battery to the alternator. On the 85 it had a wire from the junction block to the alternator. So ran a heavy wire from the battery to the alternator and all the lights work (brake lights still stay on.), now the alternator is charging, and the blower motor comes back on. I didn't check the windows, locks, or wipers.

Just because...

 

[nvrenuf]

That thing looks good!!

 

[85 Jimmy]

That thing looks good!!

Thanks! It still needs alot of work, but I think I'll take my time and do it right instead of hacking it back together so I can get it back on the road.

Another thing I had to do to it was weld up the floor pan, I did the passenger side today and I still need to do it on the driver side. Is it a common thing for the floors to crack where the front seats bolt down?

Oh, and I went out and checked the locks and windows and they atleast have power going to them, but the windows are S L O W and it took a couple tries hitting the lock switch for it to actually lock, and wouldn't unlock through the switch.

 

[85 Jimmy]

A quick question with the brake light switch. If the switch is bad would that be the reason the brake lights stay on?

How does the switch work? Does it have power all the time and with the brake pedal not depressed the button disconnects the current, and then when the pedal is pressed the button makes contact and completes the circuit?

 

[Fordum]

Yep, one side is hot, the other goes to the brake lights through the turn signal switch. Unplug the wires from the switch, and if they go off, its probably bad.

Most switches work opposite from what you would expect. When you release the brake, the pedal rises up and presses down the brake switch. That disconnects the two wires from each other.
When you press the pedal, it releases the switch and the wires make contact.

 

[frankin5]

A quick question with the brake light switch. If the switch is bad would that be the reason the brake lights stay on?

How does the switch work? Does it have power all the time and with the brake pedal not depressed the button disconnects the current, and then when the pedal is pressed the button makes contact and completes the circuit?

That switch is adjustable. see if you pull the pedal up by hand if the lights go off, if so the switch is to far away from the pedal to switch off.

 

[85 Jimmy]

That switch is adjustable. see if you pull the pedal up by hand if the lights go off, if so the switch is to far away from the pedal to switch off.

I checked that. It stays on no matter what. I'll just take the switch out of my 85 since it'll go to the scrap yard when I'm done robbing it of everything I need.