Battery in trunk....ground problem?

[Jonas_N]

I moved the battery to the trunk, grounded it in the frame under the car and grounded the engine block in the front frame. (Cleaned down to bare metal.)
Plus cable was put along the drivers side rocker on the inside then connected to the starter relay in engine bay.

Starter seemed to be very happy and started the engine in seconds.....then after a few seconds the blue cable to the wiper motor melted and the connector on the floor light switch also melted. 
Everything worked last time I started it...two years ago (With battery in engine bay.).


Notes:
-Brand new battery, fully charged.
-Old harness is a terrible mess from previous owner.
-I do have a new M&H harness for the whole car ready to be put in the car.

[Highbanked Hauler]

 When I was going to trunk mount the battery in mine someone  on here advised me to run the ground wire back to the engine.

[John_Kunkel]

Yes, using a unibody as ground can cause feedback problems with any device mounted to the body. Run the ground cable directly to the block and be sure there is a ground cable between the block and the body.

[Jonas_N]

Damn, when I allready made a hole in my new trunk floor.
Im going to weld in sub-frame connectors, though it looks like an extra cable to the front attached to the block is the way to go.

Re-think, re-do again. 

[John_Kunkel]

It's been pointed out that all modern LX cars have the battery in the rear with the negative cable bolted directly to the unibody and they don't seem to have any problems with that installation. I'm not sure what makes that installation work when some others don't.  

[myk]

Wow it's a good thing this came up as I'm going trunk mount as well...

[c00nhunterjoe]

I would be leaning towards the "old harness is a mess" part. People have run batteries in the trunks for years without issue. How does putting the battery in the trunk affect a running engine concern? He said things started to melt after it was running. Alternator is powering the car at that point. 60s chryslers are known to catch fire while driving down the road on stock harnesses, let alone a butchered one.

[Jonas_N]

I would be leaning towards the "old harness is a mess" part. People have run batteries in the trunks for years without issue. How does putting the battery in the trunk affect a running engine concern? He said things started to melt after it was running. Alternator is powering the car at that point. 60s chryslers are known to catch fire while driving down the road on stock harnesses, let alone a butchered one.

Yes, engine started very well and ran fine...then cables started burning.
Though it worked fine when I drove it a year ago. (battery at original position.)

Im very tempted to test my present battery set-up with the new harness in....

[b5blue]

FYI trunk mounted battery problems caused dash fire on my car leading to me buying the car many years ago. (Somehow positive feed grounded.) Be super careful.

[John_Kunkel]

I would be leaning towards the "old harness is a mess" part.

Or a missing ground wire. I've seen lots and lots of examples where the factory engine-to-firewall wire is missing/disconnected. When that happens the system looks for a ground path wherever it can find one and that path often can't handle the amp load flowing through it.

[krops cars]

Use heavy cables. Nice job on the grounds.

[Jonas_N]

Yeah, I use 50mm2 cables, grounds where grinded down to bare metal, shoes were six-side crimped with a prof tool. Also I have the original ground from block to firewall.

[krops cars]

Wow that is a great job. I can not believe you are getting such head aches.

[Jonas_N]

Yeah, Im in the process now installing new harness in the whole car, then I will test this set-up again, if there still are problems then I will add a cable, negative to block.

For safe testing the harness, would a 20amp fuse at the negative battery connector be ok?