Hi all,

Investigated why the reversing lights on my wifes 99' Blazer LT wouldn't work, and found that there weren't any bulbs fitted......

Put in a pair of bulbs and yay they work, check with all the other lights and they also come on when braking!!!!

Is it likely to be a fault with the park reverse neutral switch? Or has anyone else experienced the same problem and been able to fix it.

Thanks in advance

 

Is there a trailer hitch receiver installed on your truck? If so, can you tell whether or not it is after-market or manufacturer installed? Also, do you have an automatic or manual transmission? Do the reverse lights work as they should when backing up without your foot on the brake?

 

Yes there is trailer wiring installed, no idea if it's after-market or manufacturer installed, manufacturers name is Curt (if that helps)

It's an auto transmission, didn't check if they worked without having the brake on.

Thanks for the reply and hopefully this extra info helps with a diagnosis

 

Quick response until I have a chance to go thru the wiring diagram. But more questions. Basically we want to check the easy stuff first. I'm looking at a few possible culprits. Leaning towards bad wiring work when the trailer hookup was installed. It could also be your transmission range switch, or I think there might be a slim possibility it could even be related to your multi-function switch (turn signal handle), but I think that is slim. Even slimmer could be a short to power which will be the toughest to find. But again, I'm leaning towards faulty wiring. Here are some more questions to help:

1. Check from my first post if the back-up lights work correctly when backing up WITHOUT your foot on the brake. This could possibly rule out the transmission range switch.

2. What type of trailer lighting hookup do you have? Four, five, six or seven pin?

3. Is your truck 2-door or 4-door?

4. Is your shifter on the steering column or the floor?

5. Does your third brake light work correctly (the one mounted at the top of your rear window in the middle?

 

After you have determined if the backup lights work correctly while backing up without your foot on the brake, let's try some easy checks. Under your hood go to the Underhood Fuse Block (UBEC) and pull two fuses:

1. Pull the fuse "TRCHMSL". It's a 10a fuse. Then test your brakes to see if the backup lights come on. If they don't, then we are on the right track and start norrwing it down from there.

2. If there is no change, leaving the above fuse out, pull the fuse "TRL B/U". Test your brakes again to see if the backup lights come on. Just leave your truck in park during these tests. If the backup lights don't come on, replace the fuse listed in step one and test the brake again. If the backup lights continue to come on, just replace both fuses and we'll continue with the troubleshooting.

Note: You can find the position for both these fuses on a label under the lid in your Underhood Fuse Block. I am looking at a 98 but I think the wiring on a 99 is either exactly the same or close enough. Let us know what happes (along with the answers to the above questions).

 

Here's most of the answers.

2. Seven pin (but have never used it)

3. 4-door

4. On the floor

5. Yep that works

Will check No.1 as soon as I can (prob Wed night)

Will also check these Wed night.

Many thanks for the help

 

Nope, brake lights remain on when reversing.

1. Brake lights work ok, back up lights don't work at all.

2. same as 1.

Replaced first fuse not the second and everything works as it should. So for now I've left the second fuse out.

I'm guessing that's for the trailer lighting? Will it cause any issues if i leave it out? We don't tow anything so not essential.

Thanks for your help so far

 

I want to make sure I understand you correctly, you state your "brake lights" remain on when you're in reverse with your foot OFF the brake? That's a problem. Did you mean to state your back-up lights remain on?

If your lights are acting normal like they should with the TRL B/U fuse removed, there is no issue with you leaving the fuse out.That part of the circuit only provides power to backup lights on a trailer (under normal circumstances). However, that is only a band-aid for the sympton. If you want to get the truck wiring how it should be, we need to determine why there is power being supplied through that circuit when the brake pedal is applied.

I'm still leaning towards a hack job trailer hitch installement. But if you really did mean to say that your "brake lights" remain on when backing up with your foot OFF the brake as referenced in the first paragraph, then we could be looking at a problem with either your multi-function switch, transmission switch or even possibly the UBEC itself.

Do you have a DMM and are somewhat comfortable with using it?

 

What happened was:

When I brake the back up lights and brake lights came on, and when reversing with foot off the brake both both back up and brake lights came on.

But with the TRL B/U fuse removed everything works ok.

I assume DMM is Digital Multi Meter? I do have one but would need an idiots guide in how to use it properly.

I would like to get it all working correctly and appreciate your help.