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Fitting Brantz Rally tripmeter

minerva95

minerva95

PCGB Member
Member
Does anyone out that have any experience of fitting a Brantz tripmeter in a 911SC (1979)..? I have recently acquired the car and am entered into a classic rally in Greece later this year (pandemic permitting). I need to re-locate the Brantz International 2 Pro from my 944 - where the install was pretty simple - into the 911 in the next couple of weeks. Everything I am reading says that if the speedo is working (it is) then leave well alone and don't touch any wires. I also have the cruise control option, which seems to have wires on the speedo which are not on any of the wiring diagrams I have seen. The diagrams also show 2 sensor wires coming from the gearbox to the speedo - I have no idea which one I should be cutting into..? Any experience would be really helpful - I am starting to think a wheel sensor may be the safest option even with the challenge of where to mount it. Any thoughts greatly appreciated.
 
I do think also that a wheel sensor as supplied by Brantz is a good solution.

Having used the Brantz device for years we now go with GPS based apps (smart phone that is), which are very precise these days. That could be an alternative, maybe.
Not a big help, I´m afraid.

Hacki
 
Thanks Hacki - unfortunately GPS is not an option for the classic rally - only "old-school" type devices allowed.
 
Hi,
According to Bentley's Service Manual, there are two wires from the speed sensor, both brown, which become BRN/RED and go off to the speedo head. One connector then joins with a BRN at the speedo which seems to be the earthy side, the other goes to terminal 31B on the speedo (i.e. sensor input).
The Cruise Control picks up a BLK/BRN wire at a terminal marked A, and also an earth which is BRN (all on the back of the speedo).
Also there's a mileage counter (US model?) which picks up WHT/RED and BLK/BRN together also on the terminal A on the back of the speedo.
I'd guess that A is a +12v pulse created inside the speedo whereas the sensor output will be a small pulse.
Good luck with the rally.
 
Thanks for this Old and Slow - The Brantz unit is looking for an earth pulse, which is exactly how the speedo on the 944 works - 8x earth pulses from the sensor for each revolution - I'm starting to think that the 911SC sensor is sending a +12v pulse rather than an earth, which I'm not sure will work for me. I'm not finding the wiring diagrams terribly useful for this - Any thoughts..?
 
Hi,
Been busy trying to extricate the overdrive on my other car, so only just back at the laptop;
If the SC speedo output is a positive-going pulse (and I haven't found anything so far to confirm this, still looking!) then a simple transistor and a couple of resistors will convert this into an "earth" going pulse. If the Brantz input is high impedance then it might be possible to capacitively couple the signal: Can you get Brantz to advise on their input circuit? Internal to the Brantz it might already be capacitively coupled, in which case it might work on the negative edge (the back edge) of the SC pulse straight away without any need for external signal conditioning.
 
Thanks again for this Old and Slow - I've been giving it more thought, and agree with you - the output from the speedo sensor can really only be a sign wave, +ve to earth, there is unlikely to be much else going on - so the Brantz meter will most likely work without any issue. Brantz themselves did respond, but claim to have no experience of fitting to a 911 SC (seems a bit unlikely to me...) Anyway, weather permitting I'll give it a go this weekend and let you know how it works out. Thanks again
 
Good luck with it, the simple approach must be worth worth trying.
Knowing how many rallies Porsches have entered (and won!) I can't believe no one's ever done this before with a Brantz.
Let us know how you get on.
 
Brantz tripmeter now fitted and working. Turned out to be easier than I expected taking a feed from terminal 31 on the speedo. Having no air-con meant I had a spare fuse available as well. Thanks for you help with this.
 
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