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stark

Member Since: 09 Mar 2021
Location: UK
Posts: 30

Re-routing Wiring Through Chassis To Rear

I’m replacing my rear cross member with long extensions and I read on another thread about a few guys pulling the wiring out from inside the chassis and re-routing along the outside.

I can’t find the thread anymore but I’m nervous at pushing the wiring back out the way to weld the extensions in case I can’t pull it back through (as any method of doing so might melt with the welding too!) so I’m thinking on going down the re-routing option down the outside of the chassis.

Does anyone have any advice/experience or pros/cons of doing this? As I can’t think how I can leave the wiring loom in position while welding.

Thanks!

10th Feb 2025 7:43am

TVR Tommy

Member Since: 26 Nov 2013
Location: Bucks
Posts: 182

2000 Defender 90 Td5 Heritage LE Bronze Green

I pulled the rear harness out to weld on a new crossmember. Putting it back was straight forward.

Someone on here mentioned using a ping pong ball on the end of the pull wire, so it doesn't get stuck in the chassis. Worked a treat.

10th Feb 2025 7:57am

stark

Member Since: 09 Mar 2021
Location: UK
Posts: 30

What did you use as a pull cord? Did it not burn / melt during welding?

10th Feb 2025 8:33am

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17602

2007 Defender 110 Puma 2.4 DCPU Stornoway Grey

TVR Tommy wrote:
I pulled the rear harness out to weld on a new crossmember. Putting it back was straight forward.

Someone on here mentioned using a ping pong ball on the end of the pull wire, so it doesn't get stuck in the chassis. Worked a treat.

That was me:

blackwolf wrote:
... Running the harness through the chassis is extremely easy, you need a drain cleaning spring thingy (for example https://www.amazon.co.uk/gp/product/B07R289YV6 ), a ping-pong ball (you don't need a link for a ping-pong ball), and some thin rope. Make a small hole in the ping-pong ball, and fit it over the sharp end end of the spring. Secure it in place with duct tape. Now unfurl a length of rope a yard or so longer than the run of the chassis from and make a loop at the end. Attach the loop to the spring just behind the ping-pong ball. Then carefully feed the string, ball and rope into hole at the rear of the chassis and work it until it appears at the hole at the front. Pull the free end of the rope out through the hole and tie it to some external securing point. Having done this, carefully pull the spring, ball and rope back out the hole it went in (the reason for doing it this way is that it is not really possible top remove the rope fro the spring with the spring in the chassis). You will be left with a length of rope running the length of the chassis, to which you can attach the harness and pull it through.

The reason for the ping-pong ball is to ensure that the spring takes the correct route up the chassis leg and doesn't end up underneath any of the reinforcing tubes. This is important since the harness connector won't fit through the gap if this happens.

After my cross-member replacement it literally took me less that 10 minutes to run a cord up the inside of both the OS and NS chassis legs.

So carefully pull the harness out of the chassis rail altogether (disconnect the front of the harness at the connector on the driver's side of the bulkhead (assuming RHD) and pull it out through the hole at the back of the chassis). Then do your welding. The do the ping pong ball and drain spring trick. It is surprisingly straightforward.

Many people argue that it is better just to run the harness along the outside of the chassis rail anyway, citing that fact that it is visible and cannot abrade against anything in the chassis rail. My harness hadn't abraded on anything in 270,000 miles so I am not convinced about this argument, and feel it is less likely to become damaged inside the rail than outside.

Last edited by blackwolf on 10th Feb 2025 10:12am. Edited 1 time in total

10th Feb 2025 10:08am

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17602

stark wrote:
What did you use as a pull cord? Did it not burn / melt during welding?

No, because it isn't there when you weld. See post above.

10th Feb 2025 10:08am

rustandoil

Member Since: 08 Sep 2012
Location: Cotswolds
Posts: 785

2005 Defender 110 Td5 XS DCPU Bonatti Grey

stark wrote:
What did you use as a pull cord? Did it not burn / melt during welding?

When we did this job, we just used a bit of welding wire

10th Feb 2025 10:38am

stark

Member Since: 09 Mar 2021
Location: UK
Posts: 30

Thanks blackwolf, that's a great description on how to do it!

10th Feb 2025 1:26pm

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17602

rustandoil wrote:
stark wrote:
What did you use as a pull cord? Did it not burn / melt during welding?

When we did this job, we just used a bit of welding wire

This method can work, if you pull the wire through with the harness as you pull the harness out, and leave the wire in place when you weld, however there is a risk of burning through the wire or welding it to the inside of the chassis.

Do not try to pass a plain wire up the chassis leg as a means to pull the harness back though since there are various obstructions inside the chassis leg, such as spacer pieces, bolt tubes, and so on. If the wire passes the wrong side of one of these you may find that the wire has taken a route that the harness connector won't fit through. This is the reason for the ping pong ball as mentioned above - it guarantees that the drain spring follows a route along which the harness connector will fit.

10th Feb 2025 1:48pm

Retroanaconda

Member Since: 04 Jan 2012
Location: Scotland
Posts: 2699

A length of 1.5mm twin and earth cable also works well, a small loop folded into the end and secured with tape serves the same important function as the ping pong ball 👍🏻

10th Feb 2025 5:45pm

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20613

PVC coated green wire can be useful as well, it’s stiff enough to keep its rigidity, but doesn’t cause any damage, get more tricky if it’s long distance though.
I end up using 3M blue mask tape a lot as well, it has quite a lot of good uses, especially the 19mm or 20mm wide or whatever it is. Chillin In The Backwoods🇬🇧🇺🇸
⛽️🛢️⚙️🧰💪

10th Feb 2025 8:08pm

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