620 mystery wire

[76loooongbed]

Brief rundown on it. Truck is a 79 620 and all lights functional in the beginning. My heater hose starts leaking so replace them. Replace the center console and take it on a test drive. about 2 blocks from my house I smell smoke and it starts coming out from the center console and dash. I lose my regular head lights, but all of them come on with the brights. All my dash lights go dim and my signals on the dash come on. I turn around to get it home and hit a bump and dash lights brighten up and signal lights go away. While heading back, I shift gears and no response from the throttle. Pedal just goes to the floor. I reach under the dash and the clip that holds it to the pedal arm is gone the it's unhooked. I hook it back up and get home.

 

Irritated as hell at this point, I pop the hood and see that the rubber coating on my throttle cable is melted. WTF?!?! Then I move to the inside and remove the center console. I see a black wire wedged in the metal that holds the back of the center console to the floor. It's melted so I look at it and notice it had a plastic end on it that looked like it used to be a fuse holder connector (don't know what else to call it). I trace it back and it have a connector which goes to a blue wire. From there it appears to go to the main harness. The wire is still hot as it arced on the metal when I was removing it.

 

Everything works except for low beams as far as I can tell. Here's a crappy pic, but the best I could get of the mystery wire. Any ideas what I have going on here?

[ggzilla]

the rubber coating on my throttle cable is melted

That is the classic symptom that your engine is not properly grounded.

* The battery NEG cable should be bolted directly to the engine

* The engine should be bolted via thick wire to the body

 

The blue wire looks like it has an aftermarket fuse holder on it. Probably for a radio or other accessory. Not stock.

[76loooongbed]

The NEG cable is bolted directly to the engine. I'll check the wire to the body. I was thinking it was something they added too until I saw that it went into the main harness.

[moparvwfreak]

radio wire. mine was hot all the time. sounds like someone pinched the wire when installing the console.

[76loooongbed]

Solves that then. So any idea what could make my throttle cable melt? And why I have no low beams?

[datzenmike]

NO GROUND WIRE TO THE BODY.

 

The motor, tranny, diff, shocks, just about everything is rubber mounted and insulated from the body sheet metal. the only thing that directly connects the block (which is grounded) to the body is....... wait..... wait...... the throttle cable. If you should have a short or anything un-fused allowing 12 volts to touch the body it will have to travel down the throttle cable to the engine. If it draws enough current it will heat up like a toaster, melt the plastic sheath, (assuming the short is caught in time and the truck doesn't burn to the ground) the plastic will cool and harden around the throttle cable and it's now seized..

[76loooongbed]

Thanks, I'll check it out as soon as I get home from work. I got lucky and it didn't seize up my cable. Gonna order a new one anyways though.

[banzai510(hainz)]

If you got NO Low beams.

I know on 510s the relay is bad. It doesnt actually trip the realy but uses the closed contack side as a pass thru.

best to lookit up on olddatsuns.com for a diagram. If you know the pin lay out you could just make jumper wires to prove the case.

I seen people clean the contacks inside the realy and it might work.

 

 

ck and clean the fuse box but if you have HIGH beams then I will assume the fuses are good.

[76loooongbed]

I'll check that out too. Both bulbs work with the brights, but not just on reg low.

[izzo]

Hmm.

 

You know I had a similar problem. Turns out my issue was where the side marker light went down thru the body, the rubber grommet was out of place and it rubbed the wire raw and was hitting the body causing a short. Fuse kept blowing out, and the running lights would go out...

 

Might not be it, but something to take a peek at and it only takes a second.

[banzai510(hainz)]

Like I said you need the wire diagram from olddatsuns.com to give a basic idea what the LOWS go thru.

 

izzo said his side marker caused his but usually that a different fuse for those.

[76loooongbed]

Can anyone tell me or show me a pic of where the engine is suppose to ground to the frame? I'm not seeing anywhere on mine that it does.

[datzenmike]

On the 620 I think there is a black wire coming from the harness and is grounded to the body by the voltage regulator tie down bolt.

 

You can easily enough get a foot length of 10 or 12 gauge wire and crimp connectors on each end. Use an engine bracket bolt for one end and the other end to a motor mount isolator bolt.

[76loooongbed]

Sounds simple enough. Thanks Mike.

[76loooongbed]

Well finally got out to work on it and the headlights work fine now for no apparent reason. Ran a new ground wire, but the accelerator cable is definitely trashed. So I'll order a new one from rockauto and should be good to go. Thanks for the help.