Hello,


I have a 1972 Blazer that was running fine then one day after work I went to start it and nothing happened. I turned on the headlights to make sure the battery had juice and they worked fine so I wiggled some wires and then banged on the starter after doing that it started right up.



Now it doesn’t do anything, the headlights don’t work, the radio doesn’t work and nothing happens when I turn the key. I replaced the ignition switch with a brand new one but that didn’t solve anything. The starter is only a year old and works fine if I zap it with jumper cables.



Is there anything else I should check? Maybe a switch is bad or a ground wire fell off?

Any ideas of where I should start looking would be appreciated.

I would check the ground cable at the battery and at the engine.

A bad ground will drain the battery.

:alky:

This might seem obvious but clean the battery calbe clamps and posts first. If this does not work check the small wire that comes out of the positive battery cable and connects to the small junction block on the fender. This wire supplies all power for the truck less the actual starter power. Sometimes the connector on this wire can become loose or corroded. Pull the wire off of the junction block and check for more corrosion. Hope this leads you in the right direction and good luck!

Check the hot cable going from the battery to the starter, especially around the exhaust, make sure the insulation's not burned.

Thanks for the info folks, I have an Optima battery and I havent seen any corrosion around the battery cables as of yet but I went ahead and replaced both battery cables with brand new ones. I used my old negative battery cable as an extra ground cable and have it going from the engine block to the frame. I also repaired a few old wiring splices that looked iffy and I did find out that the cable going from the battery to the junction box had come undone, I reattached it and now I have constant power (headlights work, radio works,etc) but the blazer still doesnt start...it doesnt do anything when I turn the key. Does this Blazer have an ignition module near the radiator that might be dead? Any other ideas are appreciated.

Interesting…

What happens when you turn the key?

Does it make a “clicking” noise or anything?

Could it possibly be your starter solenoid?

You mentioned you put a ground from the motor to the frame. Did you have no ground from the motor to frame before?

You should be able to buy actual ground cabled to ground the motor to the frame. It is very important to have a good ground from the motor to the frame.

It would be interesting to get an amp reading of what it’s drawing when you turn the key to try to start it.

Does your dome light go dim when you try to start it?

I’m kind of wondering if you might have a short.

Coil or HEI?, if it tries to start and won't look at the coil,
otherwise not much to add to what has been said so far

think you could try another battery and check if the ignitionkey is working propperly since the starter works if you zap it with a jumpercable

I'm having a similar problem with my 72 c-20, i have power to the head lights and heater fan but the dash lights and gages don't and it will not turn over. I jumped the silenoid and can get a spark but i doesn't crank the starter. Any help would be great.

Thanks for the responses.

Bender - when I turn the key nothing happens, the starter doesnt click or do anything.....its only a year old so I doubt its dead, the starter solenoid is only a yhear old as well. I added an extra ground from the engine to the frame just in case that was the problem, plus having an extra ground never hurts and I used the old negative battery cable for this rather than throw it away, I dont have a dome light so cannot tell you if it goes dim when I try to start the rig.

LUV2XCLR8 - I replaced the entire distributor,cap,rotor,wires,etc about a year ago, I should have bought an HEI but I replaced it with a new stock distributor for a 72 blazer.

I was able to start it by jumping the solenoid, it turned over and started up.

My rig has an auto tranny and a tilt steering column and I read that these rigs may have a neutral safety switch that can go bad and cause similar problems, anyone know where the switch is located?

neutral switch is on the column down near the floor 2heavy purple wires just jump them out to c if switch is bad

Cdowns is correct above with the safety switch ^

I reread your initial post again and have a stupid question:

“Now it doesn’t do anything, the headlights don’t work, the radio doesn’t work and nothing happens when I turn the key. I replaced the ignition switch with a brand new one but that didn’t solve anything. The starter is only a year old and works fine if I zap it with jumper cables.”

Now, what do you mean by “zap it with jumper cables”?

Are you putting jumper cables to your battery, or directly to the starter???

I know this is a stupid question :lol:

The reason I ask this is a few years ago, I bought a new dimmer switch, and out of the box, it was defective. I almost ripped the thing apart to see how a brand new dimmer switch could be defective, but just returned it for a new one.

I’m kind of wondering if you may have replaced your ignition switch with a bad one.

That’s the way my luck is.

I would try what cdowns said above first, jump out the safety switch and see if that works.

If I remember correctly, the power runs into the ignition switch, out of the ignition switch into the neutral safety switch, to the starter.

If you jump out the switch and it still doesn’t work, I would put a meter on the jumped wires and check to see if you have 12v when you turn the ignition switch to the ‘start’ position.

If you don’t have 12v there, I would really question the ignition switch.

I'm having a similar problem with my 72 c-20, i have power to the head lights and heater fan but the dash lights and gages don't and it will not turn over. I jumped the silenoid and can get a spark but i doesn't crank the starter. Any help would be great.

I’m assuming you jumped the solenoid with the ignition switch in the “on” position???

Are you sure your battery is good? Did you try jumping it with another?

It would be kind of nice if you start a new thread on your problem so we don’t get too confused :lol:

Well folks I had some time to work on the Blazer over the weekend and decided to rip out the starter I bought last year and have it tested.

It failed the testing so the auto parts store I bought it at gave me a brand new replacement starter, I installed it in the Blazer and voila it starts right up...thanks for all the advice and thank goodness this problem has been resolved I was just about ready to rip out all the wiring and install brand new wiring.

Glad to hear you got it fixed.