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Discussion Starter · #1 ·
about to put a tow hitch onto my 2006 Wagon here in Australia.
mechanical fitting no problem, but have a quick question about the wiring to the plug.
i have read a few posts on here about using a separate relay box to go between the original harness and the plug to isolate them.
what is the reason for this, will it cause major problems if just spliced in?
is the extra load of the trailer lights too much for the existing wiring and causes problem with the electrics/canbus?

on other older cars i have done, we normally just splice into the wires with no problems.

the same box i have seen used on here for <50$, that same unit costs around 200-300$ down here from a trailer supplier......
 

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2006 Chrysler 300c SRT8 w/ a Hellcat Supercharger
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From what I can tell, that box serves the purpose of three 12v relays, one for brakes, and one for each turn signal (unless your trailer only has brake lights). You could achieve the same effect by wiring three 12v relays to a good 12v source apart from the canbus each triggering with its respective triggers (positive brake light / turn signal wire). I am not sure if the extra load will cause an issue with the canbus where you will need the box in the first place. You can always try it out and let us know, either way you will have to cut into the harness. If you had a set of LED trailer lights I would guess there would not be enough extra amperage to trigger any fail safes.
 

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Hello mate;

Firstly, I have a 2007 300C here in Oz. So I assume mine is same as yours.

You have probably read all the "American stuff". Like I did.

AFAIK - the American ones still have the "stop light flashes for indicator" thing. Maybe a hassle when hooking up a trailer; but not relevant to us, as we have a completely different system.

Our cars have totally separate indicator/stop light circuits; as do our trailers.

The other thing everyone panicked about was the "canbus senses extra current/puts up a fault." Mine doesn't.

I fitted my tow bar 8 years ago, and just hooked up trailer lights to the wires going to the stop/tail/ind. No warning lights = no problem. I put a very small fuse box in the boot with a fuse for each "stop/tail/indicator", so 4 fuses in all. Maybe overkill, but a short in the trailer (most trailers a lot more manky than cars) without that would blow car fuse anyway. Low fuse rating in the "new/trailer" box means that will blow before car one usually.

Initially my trailer had normal globes in it (stop tail 5/21 watt, indicator 21 watt); but then fitted LED ones, as easier. more reliable. They draw stuff all.

But the point is - the American system for stop/tail ind = totally different as far as I know, but could be wrong; anyway, doesn't apply here. And my CANBUS never detected a problem when normal lights on trailer; but if you are concerned, put LED lights on trailer (combined lens clusters cheap now) and the little fuse box gives complete peace of mind.

As quoted above, "J2Hlabs" is exactly right/same as my experience.

"I am not sure if the extra load will cause an issue with the canbus where you will need the box in the first place. You can always try it out and let us know, either way you will have to cut into the harness. If you had a set of LED trailer lights I would guess there would not be enough extra amperage to trigger any fail safes."


Disclaimer - info for info only. Do your own research/make sure you are happy with the theory above. Your car, your loom.

Cheers - Ken H
 

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PS.

That box "unloads" the cars elec circuits by using the signal only (voltage level, draws no current) and switches power through to the light on the trailer from a separate power source from the battery, so NO load on the "trigger" circuit.

You could achieve the same with normal everyday relays from any auto shop, but messy/bulky, need 4 relays. Each relay draws very little current; hence driver circuit "unloaded" similar to the "box" above.

Your decision. Have a look and decide - The theory should be (Quick calculations off the top of my head; but should cover it);

Tail draws nothing; but lots of small lights hanging off it. Two tail globes on a trailer = 10 watts. Just under an amp. Tail circuits on car run SO MANY running/instrument/interior illum lamps. Probably a few amps.It IS possible CANBUS could sense a minimum current draw/sense when a globe is blown; and the trailer could "mask" that indication, ie blown tail light globe not "seen" as trailer light draws current normal tail globe would. But then tail light out/trailer on (who cares?); then show up when you disconnect trailer.

Stop CCT draw 2 x 21w = 42w = 3.5 amps (plus hi level stop lamp). Trailer is another 3.5 when braking.

Indicator normal draw 2 x 21 = 42w, + side lights (about another 5W) so approx 4 amps intermittent, trailer 21w - almost 2 amps.

So get the box/get relays - NO extra draw. No box = Double current when braking, 50% more current for ind cct.

Or get the LED's = hardly any extra draw = no complications/boxes.

I don't tow trailer much anymore, but have used mine and multiple "Bunnings" trailers with standard globes since 2013 on mine. No dramas.

Ken H :)
 

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about to put a tow hitch onto my 2006 Wagon here in Australia.
mechanical fitting no problem, but have a quick question about the wiring to the plug.
i have read a few posts on here about using a separate relay box to go between the original harness and the plug to isolate them.
what is the reason for this, will it cause major problems if just spliced in?
is the extra load of the trailer lights too much for the existing wiring and causes problem with the electrics/canbus?

on other older cars i have done, we normally just splice into the wires with no problems.

the same box i have seen used on here for <50$, that same unit costs around 200-300$ down here from a trailer supplier......
Further to below; If you wanted to go the "bank of relays" route; it is simple enough to wire, but a bit messy; hence why the box for convenience.

12V micro relays are cheap enough, can get 4 for about $30; but the sockets are expensive ($8 each). But neat, they normally "clip together" for a bank of 4 relays (stop/tail/ind/ind). So cost about $70 if you really want to do that.

Plenty of electronic "boxes" on the internet; but most are either for the "American merged ind/stop" line in (NOT ours) or Euro ones (who knows??).

Here are some links if you like. I can tell you how to wire it up if you need it, but you'll probably work it out, quite simple.




And - might be more convenient - Jaycar have them in stock for 8 bucks each for both socket and relay. Works out at approx $64 for 4 of each.

Examples only to show what you can get. Do your own research.
 

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Discussion Starter · #6 · (Edited)
thanks for your very detailed explanation, there not a lot of info out there for us ozzies.... everything relates to either the UK or US models.
i was going to wire up my own relays for safety, but i managed to find the relay box on amazon for 54$ delivered.
will possibly be towing older (filament) and newer (led) trailers, so i'll probably use it for piece of mind.
(could sell it and triple my money to an uneducated person...)
even local towbar suppliers cannot tell me if anything is needed for the wiring on a 300c or if it will cause any problems.

on another note about local towbars,
the hayman reese towbar i purchased didn't come with a hitch, do you happen to know what offset/drop bar you used when towing that suits a 300c?
was your rear bumper cut to fit around the bar?
 

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thanks for your very detailed explanation, there not a lot of info out there for us ozzies.... everything relates to either the UK or US models.
i was going to wire up my own relays for safety, but i managed to find the relay box on amazon for 54$ delivered.
will possibly be towing older (filament) and newer (led) trailers, so i'll probably use it for piece of mind.
(could sell it and triple my money to an uneducated person...)
even local towbar suppliers cannot tell me if anything is needed for the wiring on a 300c or if it will cause any problems.

on another note about local towbars,
the hayman reese towbar i purchased didn't come with a hitch, do you happen to know what offset/drop bar you used when towing that suits a 300c?
was your rear bumper cut to fit around the bar?
Hey mate;

As far as drop hitch or whatever - I originally wanted the one with the removable "tongue" (they had a square section one with a pin that slid through to lock); but when I looked at the specs, they had that, and they had a lighter duty one; and as I don't tow huge boats and car trailers like I used to (my 300 only the V6; so........) it was easier to get the standard one. That has the tongue held on by 2 bolts; I thought I could remove that if I wanted to, but have never had to, as you hardly notice it/is unobtrusive. I didn't have to cut anything; and the heavy duty one should be same height; so should just fit as well; but haven't fitted, so can't say for sure. As I am in Perth, I wanted the 7 pin small round plug (most common here) and they supplied that with the towbar.

I bought mine from a local towbar place here (Perth); they delivered it cheaper than any I found on the internet, so was pretty good.

Good score with the box on Amazon. I buy the world on Ebay; have had mixed results on Amazon, as many "not send to your country"; but if you have found, good score.

Just be careful when you get it that it is for our system; so many are for the US ones.

What you said about "even towbar place didn't know..." That is actually good that they are honest. Many are NOT elecs; and just "wing it.."

Good luck with it mate.

It is a minefield commenting on elec matters for cars on forums. If too little info = get hassled. If try and explain (to make sure people understand/don't fry their gear); "too involved/treat us like idiots". So easier to just delete, or not comment in the first place. So I am relieved you took the comments above in context/just trying to help.

If you have any hassles/questions about the box when it arrives, just buzz me back here - but you should be right.

Cheers;

Ken H
 
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