Two wiring questions

[rationull]

Hopefully this is on topic enough.. I'm installing an electric trailer brake controller in a 99 chevy suburban and I've got a couple of general questions about wiring (not specific to brake controllers).

1) The documentation recommends I wire the controller ground directly to the battery (the controller is of course mounted in the cabin). The truck, being a GM, has side-post batteries. What's the best way to robustly hook up a new wire to the battery terminal?

2) I can't find any convenient opening in the firewall to route wires through, so I think I'm going to have to drill through. What's a good way to insulate the resulting hole and protect the wires from the surrounding metal?

Please forgive the basic questions. I'm not all that knowledgeable mechanically but I'm more comfortable with that than with wiring!

 

[javacontour]

If you have good grounds, it really shouldn't make a difference.

If I felt the need to ground at the battery, or at least close, I'd find the closest ground block to the negative battery cable in a side terminal application.

However, I think a ground point INSIDE the vehicle would be cleaner, as it's not exposed to weather, etc.

Before I'd go drilling holes in the firewall and putting grommets in there, I'd try grounding inside the cabin, and perhaps cleaning up any ground connections to the body of the vehicle under the hood.

If it works well, then go with it. I probably wouldn't try to go directly to the battery unless I was having issues.

 

[The_Jeff]

You should be able to find a huge (rubber covered) hole with a thick wiring harness going through it, and a grommet formed around said harness. About 1/2" away from the wiring bundle poke through with a drywall screw, then use the threads on that screw to chamfer the hole open. Put a drop light on the floorboards so you can see the light through the hole you poke.

I assume this gizmo needs a master cylinder connection as well as the cab mounted panic lever, so going through the firewall is a must.

 

[George7941]

I agree with everything Javacontour said.

If you still feel the need to run a wire to the battery, check out DelCity.net. They have side terminal bolts that are extra long and are threaded at the outside end, enabling you to attach extra cables to side terminals.

 

[Jimmy9190]

On the Suburban there should be a large rubber grommet you can see from inside the vehicle, from under the dash. It is in the left corner/side area as you look at the firewall from inside the vehicle. The large main electrical wire harness runs through it. Do as posted above, cut a hole to one side of the harness. A razor knife or sharp pocketknife will work, but I use an old fish filet knife for grommets. You can then pass a piece of stiff wire (like a cut-off piece of a coat hanger) or use what I use which is a long air conditioning zip tie with the end cut off. You can get those at any Home Depot, Lowe's, etc. The zip tie does a nice job because it's flexible and not likely to damage any wiring or other components it may come into contact with during this process. Once it's through the firewall, use electrical tape to attach the wires you need to pass through to the engine compartment. Plus the ridged surface of the zip tie allows the taped on wires to sort of grip on and not be likely to slide off when pulling through the grommet. You can use vaseline, WD-40 or windex on the taped up wires to help ease them through the grommet. Then you can use either Permatex silicone or sealing putty to seal the hole in the grommet and prevent any water leaks.

As for the ground, there are any number of good solid grounds inside the vehicle. There really should be no need to ground to the battery. Remove the driver's kick panel trim (it should just pull out, it has metal and plastic snap-in retainers) and you will see some large bolts there that hold the lower corner of the dash in place. You can ground your controller there under one of those bolts without any problem. You could also pull up the carpet and ground it to the bolt holding the seat belt retractor unit to the floor.

As for the battery connection, follow the positive battery cable out a foot or so and you should see a threaded lug there where it splits off to the starter and alternator. It may be covered with a red plastic cap. Or if your truck doesn't have that, you can go to the under hood fuse box and tap into the main battery feed there. If you have to connect straight to the battery, any good car audio shop, Circuit City or Best Buy will have GM battery terminal adapters for sale which will make it easy to connect to the battery post. Or you can get them online like George stated above. No matter where you connect for battery power, place an inline fuse connector no more than 6 inches from the connection. That will prevent a fire hazard in the event the main power lead for your controller should short out to ground. Use the same amperage rating fuse as is provided with the controller unit.

Hope this helps. Good luck with it.

 

[Tosh]

Originally Posted By: rationull
1) The documentation recommends I wire the controller ground directly to the battery (the controller is of course mounted in the cabin). The truck, being a GM, has side-post batteries. What's the best way to robustly hook up a new wire to the battery terminal?

That's an odd recommendation because the end of this long wire will actually be further from 'ground' due to its length. Try what Javacontour said.

 

[rationull]

Thanks for the many responses.

javacontour: I agree that inside seems like a better idea. I'm not sure exactly what I'll do as the controller's installation instructions specifically say to attach the ground to the battery. I think they just want to make sure you get a good consistent ground that doesn't corrode (since an inconsistent ground would cause intermittent braking failures). I will have to route wires through the firewall for positive and for signal wires anyway, so grounding inside the cabin wouldn't save me the trouble of drilling through the firewall.

Thanks for the advice as to how to get through the firewall. I didn't think it was feasible to come through the same hole the wiring harness goes through because on the inside, the entire hole is covered by the plastic panel with a bunch of spade terminals and sockets on it. I'll check it out again to see if I think I can poke through it instead of drilling a new hole.

I'll check out some shops to get a longer, threaded side-post terminal. That would be perfect.

No master cylinder connection necessary, this controller is purely for electric brakes.

Jimmy9190: I won't have to go directly to the battery for a positive connection, and I won't need an inline breaker. This truck has a couple of auxiliary power studs coming off the fuse box, each of which is fused to 30 amps.