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smh00n

Stop light and indicator wiring on a 70

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Being in Australia, we have a crazy law that requires both stop lights to be illuminated together - so the red indicator function needs to go.

Where in the loom does the indicator/stop light happen? I'll try to split the wires and put in a separate bulb for the indicator. 

 

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Turn signal and stop lamps are combined together in the turn signal switch.  There's no easy way to disentangle the two when the two signals share the same filament.

The stop lamp signal is a green wire, 2nd from the end on the bottom interior curve.  The rear turn signal leads are green/orange (left) and orange/blue (right) at the turn signal switch. 

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Thanks. So, do the stop light wires go through the turn signal switch? Would it be easier to run a new wire to the stop lamps?

I was thinking that I could put in a divider inside the bucket/housing for the outer lens of the lamp, and use the outer third lens as the indicator light (I can use a red indicator lens) and use the inner two for stop lamps, again with a new holder to brighten them up. Would that be less effort? 

I'm a bit sick of idiots nearly rear-ending me due to being on their phones and dim stop lights not really indicating when I am stopping.

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I'm not sure that would work.  Yes, you can bypass the turn signal switch for brake lights, and convert one bulb to turn signal only and the other to brake lights.  The problem lies in the side marker lamps which don't have a true ground, but compare voltage of turn signals to running lights. 

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Maybe bigmal will drop by here, or you can send him a message. He also lives down under and has a 70. I have a post here that describes the 70s turn signal system, and he said it helped unscramble the problem. Perhaps he can guide you through what he did. Look in "How to's" for "1970 Mustang Exterior Lights (turn signals)".

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Pgold that's similar to what I was thinking. I'll have to get time to look at the whole set up and see how I can change it. I'm thinking maybe change the side lights to just marker lights.

The whole 70 alternating indicator and side light thing has stumped me, and now may explain why the repro front indicators I used seemed to not work properly. The indicator bulb was on at park and the side light bulb flashed (basically, reverse of what should have happened) so now I need to spend some time thinking this through. One of the joys of buying another mans project :(

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31 minutes ago, smh00n said:

Pgold that's similar to what I was thinking. I'll have to get time to look at the whole set up and see how I can change it. I'm thinking maybe change the side lights to just marker lights.

The whole 70 alternating indicator and side light thing has stumped me, and now may explain why the repro front indicators I used seemed to not work properly. The indicator bulb was on at park and the side light bulb flashed (basically, reverse of what should have happened) so now I need to spend some time thinking this through. One of the joys of buying another mans project :(

That problem is due to a very bad design issue by Ford (which was corrected in following years).  There are no true grounds for the side marker lamps, instead the lamps light up when there's a difference in voltage between the turn signal and the running lights.  This means that the turn signal lines or the running light lines act as a ground and that there is voltage/current bleed-through from one to the other.  This makes trouble-shooting near impossible.  Bad Boy, Ford, Bad Boy! 

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On 7/25/2021 at 11:19 AM, Midlife said:

That problem is due to a very bad design issue by Ford (which was corrected in following years).  There are no true grounds for the side marker lamps, instead the lamps light up when there's a difference in voltage between the turn signal and the running lights.  This means that the turn signal lines or the running light lines act as a ground and that there is voltage/current bleed-through from one to the other.  This makes trouble-shooting near impossible.  Bad Boy, Ford, Bad Boy! 

The Fraud Motor Company outdid themselves on this one alright. I stripped back the harness on the driver side yesterday - soooo many black wires! 

I think I have identified the wiring I need; it turns out the PO had already run a new brake light wire and has hacked up the OEM harness, so I believe I can just cut one wire and put it to the new indicator bulb. 

Watch this space.

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