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Topic: Sentry system sensing a headlight out (Read 4276 times) previous topic - next topic

Sentry system sensing a headlight out

Reply #15 –
Softtouch, there is a cleaner way, how to fix this problem. There is no need to cut anything under the instrument panel. Just at the relay, closer to the lights, cut that R/BK wire, add 0R082 / 5W resistor and cut BR/P wire from the original splice S118 and conect it behind this resistor, closer to the lights. This should work well.

Sentry system sensing a headlight out

Reply #16 –
Help me out here Trinom, I am confused. Not an unusual state of mind for me.
Lets say we have 12.5v and we want 12v dropped across the parallel bulbs and 0.5v dropped across the series resistor.
Lets round that off to a 24/1 ratio.
45w lo beam bulbs would draw about 3.7A at 12v giving the bulb an effective resistance of 3.25 ohms.
Two bulbs in parallel 1.63 ohms.
1.63 ÷ 24= 0.067 ohms for the series resistor.

Sentry system sensing a headlight out

Reply #17 –
I have come to the conclusion that the "resistance wire" shown in the EVTMs lamp-out warning diagrams is not a special wire.
It is the normal hook-up wire. The warning module is sensing the normal voltage drop (0.5v) across a length of wire.
For the low-beams it is sensing the voltage drop across the wire from S117 (RH side of steering column) to S118 (LH front fender apr0n).

If someone with a relay set-up can make some voltage checks, we can see if the "fix" can be as simple as relocating the "sense " wire on S118 to some spot in the relay circuit harness.

Measure from battery + to the splice where the cable splits to go to the separate low beams. This would be the max voltage drop available.
(This means putting the positive meter probe on the battery + and the negative meter probe on the cable harness splice.)

Moving the "sense" wire to the relay circuit harness will be running a hot wire into the cabin. So the fusing of this relay mod will be a concern. We don't want an unfused hot wire running to under the dash.

Sentry system sensing a headlight out

Reply #18 –
First of all, your alternator makes approximately 14 volts. All the bulbs are made for 13,8V in according to datasheet, so there is no need to calculate a dropping resistor in this case.

I_bulb = 45 W / 13,8 V = 3,3 A -> 2 bulbs take 6,6 A.

then you need a voltage drop 0,5 V on the resistor in series with both bulbs

R = 0,5 V (drop) / 6,6 A = 0,075 Ohm.

So you are right, I have some mistake in that resistor calculation. The closest higher available value is 0R082, which will be fine.

The rest of my picture is correct. Fusing that BR/P wire isn't bad idea, but it's not necessary, because the circuit is fused before relay, which is the same way, as it used to be. 15A fuse should be fine.