This is my first post and I am not happy making it a request for help! I have been hoping to ADD to or HELP someone on the forum. Anyway, I have started to help a neighbour with his LX ss Hatch with 308 and T10 trans with L34 rear end and all the flares etc. It will be a very nice car. My question is that Its electric fuel pump should stop IF the engine stops with the IGN still on (hope it wont ever!) so I have a spare wire leading from the engines standard oil gauge sender area to be used to ground out the fuel pump relay when the oil is over .3bar (Tridon part TPS040 N/O oil switch). Can anyone help out with info on a manifold to allow the 2 switches. Original one appears to be 1/4 -18NPT and the second one is M10. OR is there another port that I can use elsewhere on the engine? For the obvious problem of the starting before oil pressure is up I propose the park brake circuit will allow the relay to close making the FP work when stationary.
I really appreciate the forums help and have been very impressed by some of the people who contribute....there is some great and awesome knowledge out there.

Earlier red 6 cyl manifold vacuum brass T-piece. Like HK 186. The one the disc brake booster attaches too. It will screw into the oil pump and will accept 2 x senders. This is what i've used for 304 EFI conversions into HQ-WB so the EFI sender can be used as well as the GTS guage sender.

For my electric fuel pump to work correctly, I have used an LPG shut off timer.
With a wire connected to the coil, if it receives coil pulse, it stays closed & powers fuel pump via a relay.
If it receives no coil pulse, it will only stay closed a few seconds, then open, shutting the fuel pump off.
Simply put, the fuel pump will not operate without the motor running.
The biggest problem this solves is in the case of an accident. Pumping fuel is not a good thing.

This car runs MSD and has no wire for a FP which is strange. I did not want to mess with it at all. Keep it standard. Alternator W point with special ac relay can be used but not so good relying on a belt and it to keep working. If oil press drops it might save the engine from further damage. Its simple and when the car is miles away from me I like the KISS principal. We will talk it out together today when we get back to working on it.

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Originally posted by Dr Terry

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Originally posted by hk307
HINT; never offer to wire a hazard flasher switch to a car that uses indicators as reverse lights. If you do it can be done but allow about 5 relays and a double pole dash switch...

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Or just a single pole switch & 3 diodes.

Dr Terry

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I hoped no one would pick this up!
I did think diodes but went relays as i thought 2 would do avoiding volt drop and having 40+ watts (or 80+) going thru them.
BUT 2 relays soon got to more. when hazard switch is used then: I had to change flasher from ign to bat feed.
then isolate ign to rev sw, then join both reverse wires, join both front lamps, join both rear lamps and front lamps to flasher. That makes 5 relays so diodes will be used next time for joining lamps and maybe relays for main power requirement.

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Originally posted by hk307
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Originally posted by Dr Terry

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Originally posted by hk307
HINT; never offer to wire a hazard flasher switch to a car that uses indicators as reverse lights. If you do it can be done but allow about 5 relays and a double pole dash switch...

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Or just a single pole switch & 3 diodes.

Dr Terry

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I hoped no one would pick this up!
I did think diodes but went relays as i thought 2 would do avoiding volt drop and having 40+ watts (or 80+) going thru them.
BUT 2 relays soon got to more. when hazard switch is used then: I had to change flasher from ign to bat feed.
then isolate ign to rev sw, then join both reverse wires, join both front lamps, join both rear lamps and front lamps to flasher. That makes 5 relays so diodes will be used next time for joining lamps and maybe relays for main power requirement.

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Voltage drop isn't really a problem, 40 or 80 watts doesn't go thru anything. Current goes 'thru' the diode & amps is the measure of current. Each globe draws less than 2 amps (watts = volts x amps). 2 amps per diode is easy & the voltage drop per diode is much less than one volt, you wouldn't notice the difference in brightness.

The simplest method is 4 diodes, which is one to each corner lamp. I found that using only 3, by running one to the reverse light circuit is the easiest. I've been doing it this way for nearly 40 years, with no dramas.

Getting back to you oil pressure switch fuel pump wiring, a tachometric relay (as mentioned) is another way to go. An oil pressure switch & a relay is very old school, but simple, reliable & cheaper than a tachometric relay.

Dr Terry

when the bowl is fuel there is a slight back pressure about 4 1/2 psi, this causes the float needle to block the inlet , the extra fuel is bypassed back through the pump.
I have used the lpg setup for years, reliable and cheap to replace if it breaks.
I notice everyone uses relays.
while relays have their place they really only replace decent heavy duty wire and allow you to use a lighter gauge wire. if you use a heavy enough gauge wire the need for a relay does not exist and is one less thing to go wrong, and several less connection points to go wrong. every time you put a joint in you introduce something else to go wrong, whether through dirty /loose joints, solder failure, or whatever.
A good indicator is feel the wire after it has been running for a while. if the wire feels warm it is too small and the electricity is being wasted off in heat.
incidentally if you do get an under bonnet fire do not open the bonnet unless you have a hose or extinguisher handy. from bitter experience in three cases I have found that as soon as you open the hood the air gets in and you have a raging fire. the flames just roar out. in the third case I just popped the bonnet open to the catch, and squeezed the hose in sprayed plenty of water in until the flames went out then opened the bonnet and sprayed the smoking interior, in that case the car was saved in the first two it wasn't although in one of them a whole fire extiguisher was emptied into engine bay..

true, when running heavy current draw devices like electric cooling fans or driving lights it is essential to take as much load off the switches as possible but this application is not a really heavy current one. When I put the driving lights on my HQ I had to run a relay from the dipswitch as it cooked very quickly with all that current going through. I wouldn't bother with a relay to run the fuel pump tho.
everyone to what works for them tho. where would be be if everyone did the same?

Edited by user Sunday, 27 January 2013 9:38:04 AM(UTC)  | Reason: Not specified

So It comes down to tachometric relay: cant be used with MSD ignition, refer their own web forum, Alternator W point as gemini: yet another relay but a special ac one, so for KISS principal we have decided on .3 bar N/O oil switch sitting on VDO adaptor. With starting bypass via the redundant coil terminal of the ign switch the FP will work when the key is held just before start position.
Also as a fault diagnosis or to get home if all else fails he can move the FP fuse over one position and it will power directly the FP circuit.

the yellow wire in the original specification is the resistor bypass while cranking.
now not required with msd system. it is signaled by power on the pink ign circuit which remains active on the start and run position of the ignition switch.