Heater shuts off if headlights are on

I have a 98 Tacoma and as soon as I turn my headlights on my heater shuts off, so I am having to pick between one or the other to get to work. I just picked up the truck as well. Any ideas of what it could be?
Thanks!

 

Could be a lot of things, really. A very low battery, an alternator that's not putting out the proper voltage, a previous owner's hacked wiring...

Start with the simple stuff first. Check the voltage and charge on the battery and have a local shop test your alternator. Whenever I've run into high-draw electricals not working at the same time, it's almost always been one or the other.

 

Great advice, and I wouldn't wait too long. I was driving down the interstate highway here in N.C. at 2am one night driving into work for an after hour emergency, and bam, dash lights went out, then the head lights, and the car died right after that. So have it checked out, because once the alternator quits charging the battery goes really fast.

 

Thanks for the advice! I will start there and see what I can get figured out!

 

A Multimeter is your friend so is having the Toyota Electrical Diagrams for your vehicle.

It makes chasing electrical problems less frustrating

 

The battery tested weak, alternator was working properly, put a new battery in, starts faster and dash lights are brighter but no luck on the problem. Headlights and heater work flawlessly when the truck is not running, once truck is running is when the heater stops when headlights are on. Fuses are good to headlights and heater and relays are good I will have to start checking schematics. Also going to check ground straps.
thanks!

 

When you say the heater stops . . . you mean it stops blowing air altogether, or the air that it's blowing stops being hot?

 

Sorry I mean the blower motor shuts off. No more air comes out of the vents

 

Time to pull out the overall Electircal diagram and see if those two share a common ground or something.

 

This smells like a groud issue to me. I would start by turning on the blower, and then have someone turn the headlights on and off while listening/touching the Heater Relay. If it clicks, then its shutting off and we've narrowed down the problem a little.

 

I think the boys are onto something. Start hunting a grounding problem. Or a relay. I hate chasing electrical gremlins.

 

Really Curious to see how this plays out.

 

I have fixed the ground wire from motor to firewall, and got a new ground from battery to body. I cleaned battery terminals really good, going to start looking a lot more in depth tomorrow. Also low beam lights have stopped working(fuses still good). High beam lights do work but the blue high beam dash light no longer lights up. No luck with the heater and lights working together at this point.

 

If the low beams are not working, sounds like the dimmer switch (multi function switch) is bad. It's easy to replace the turn signal/dimmer switch.

I just did this. I went aftermarket and it worked fine. I think I paid $40.

 

I will test that!

 

Checked the multifunction switch. Replaced with new and no luck there. There is lots of wiring problems with this truck the farther I get into it..

 

Still have been unable to solve the problem.. not sure what the next steps could be. Bad computer?

 

I'm sure you've already checked all of your fuses. The only thing that comes to mind are the wires short circuiting with each other somewhere where they make contact

 

Did you have any luck with the heater relay? Is it clicking on and off with the headlights?

No computer involved here.

 

It could be. It only happens while running. When the truck is in the on position not running, lights snd heater works. Running you have to pick one or other. Could be the ignition?