Brain teaser....

[RealMcCoy]

Today's Patient is a 73 240Z with a small block chevy swapped in... I got it because there were unresolved wiring issues that needed solved. There is not an inch of original Datsun wire harness in this car. It has had an aftermarket street rod type wire harness and fuse box swapped in, it's a GM style harness, and the car has a GM steering column installed.

The brain cramp came when I started trying to figure out how to make the Datsun wiper motor work with the GM column mounted wiper switch. The Datsun wiper motor is controlled by three wires grounded by the switch. When in the off position, no wires are grounded, when in low speed, the blue/white and blue wires are grounded, in high speed, the blue/white and blue/yellow wires are grounded.

The GM switch has two control wires, when in the off position it grounds the grey wire, when in low speed it grounds the purple and grey wire, and when in high speed it grounds the purple wire only...

So with two five pin Bosch style relays and the GM switch, duplicate the Datsun wiper control.... Anyone want to take a shot?

It made my brain hurt for over an hour... Then when I figured it out I felt really stupid and thought I should have figured it out in a few minutes...

The sketch is a diagram of the Datsun and GM switch contacts...

[IPD]

No, sorry. Not taking any shots. I'm done doing mechanical/electrical modifications to any vehicle ever again.

[95gto]

If I got this right you should have been able to wire it this way:

R1:
30 = Ground
85 = Purple
86 = 12V
87 = Blue/White Wire and R2-30
87A = Open

R2:
30 = Blue/White and R1-87
85 = Gray
86 = 12V
87 = Blue
87A = Blue/Yellow

[RealMcCoy]

If I got this right you should have been able to wire it this way:

R1:
30 = Ground
85 = Purple
86 = 12V
87 = Blue/White Wire and R2-30
87A = Open

R2:
30 = Blue/White and R1-87
85 = Gray
86 = 12V
87 = Blue
87A = Blue/Yellow

You are on the right track, and getting very close to what I ended up with, but your solution bridges the blue/white and blue wires with the switch in the off position...

[95gto]

You are on the right track, and getting very close to what I ended up with, but your solution bridges the blue/white and blue wires with the switch in the off position...

You didn't use a switch output to supply direct ground to one of the wires did you?

[RealMcCoy]

You didn't use a switch output to supply direct ground to one of the wires did you?

Can you think of any other way to make it work without throwing in a third relay...?

Yes, that's exactly what I did. It's wired just like your example, except the blue/white wire is tied into the purple lead at pin85 of relay 1.

[AdamVR4]

No, sorry. Not taking any shots. I'm done doing mechanical/electrical modifications to any vehicle ever again.

cool story..? the fuck.

[box]

At a glance, I'd do it as follows;
Relay 1:
85 - Ign
86 - Blue/white wire (from motor), Ppl in GM switch
87 - Blue (from motor)
30 - Pin 87 on Relay 2

Relay 2:
85 - Ign
86 - Gry in GM switch
87a - Blue/yellow (from motor)
30 - Gnd

GM Switch is off, Relay 2 is energized, Relay 1 is not. No motor wires are grounded.
GM Switch is on low, Relay 1 is energized, Relay 2 stays energized. The blue/white motor wire is earthed via pin Ppl on GM Switch, the blue wire is earthed via relay 1 and 2.
GM Switch is on high, Relay 2 is de-energized, Relay 1 stays energized via pin Ppl, blue/yellow motor wire is earthed via Relay 2 NC contacts, blue/white motor wire stays grounded via pin Ppl, blue wire is no longer grounded due to Relay 2 NO contacts being open.

I think. A diode near the motor on the blue/white wire may be needed.

[95gto]

Can you think of any other way to make it work without throwing in a third relay...?

Yes, that's exactly what I did. It's wired just like your example, except the blue/white wire is tied into the purple lead at pin85 of relay 1.

Not with Bosch style form C relay, hence the question. Are you worried about the switch not being able to handle the current draw of the wiper motor?

[RealMcCoy]

I think. A diode near the motor on the blue/white wire may be needed.

I'll let testing decide if that's an issue, I considered the possibility that there could be power on the blue/white wire while the switch is off, but the motor was in the process of parking. That could potentially disrupt the parking process if the back feed opened a relay back up. I don't think you could put the diode in the blue/white wire though, as the current flow would not be changing direction between normal operation and the potential problem condition. In the purple wire between the blue/white wire and the relay would work.

Not with Bosch style form C relay, hence the question. Are you worried about the switch not being able to handle the current draw of the wiper motor?

No, not at all... Both the Datsun system and the GM system grounded the motor through the switch contacts from the factory, and used a similar current draw motor. The entire purpose of the relays is to direct the current properly. I'm not worried about saving the switch from normal current flow.