I installed powerseats in my 124 which did not originally come with power seats, i have just recently acquired the powerseat switches. I'm missing all the wiring and the control box. It's very difficult to acquire parts where i live, so i think it would be easier if i just made my own "relay box"

anybody have ideas on how to make one from scratch?

my main concern is how to wire the relays and how many relays do i use? i'm thinking 4 for each motor, 2 would turn the motor one way and the other two would turn the motor the other way. for a total of 20 realys?!?!?!

although the switch by itself is constructed in such a way that when toggled it reverses polarity to the motors, thereby turning the motor both ways. I don't want to have to wire the entire thing through the switches. That's why i need to install relays, but i don't really know how to go about it. The original mercedes control box uses just 10 relays, i'm guessing that's 2 relays per motor, as there are 5 motors. I just can't see how they made it work using just 2 relays per motor. HELP!!!!

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85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project

Relays are used to switch higher currents. It's easier to switch 15A with a small switch energizing a coil with a beefy set of contacts than to design a switch that has a light touch and 15A contacts.

A starter solenoid is an example where a very small contact in the key tumbler switches very high current, on the order of 100A-400A. Without the solenoid, the switch would have contacts so big you probably could not turn the key using both hands!

You need at least two relays for each motor.
-One (forward) is wired +/+, -/- (battery positive to motor positive) to spin the motor one direction.
-One (reverse) is wired +/- and -/+ to run it backwards.

You wire battery positive to the common of the switch. Pressing in one direction closes the 'forward' contact and energizes the 'forward' relay. Pressing in the other direction closes the 'reverse' contact, and energizs the 'reverse' relay.

I don't know how the W124 seat is wired, but this is a general overview of the theory.

I hope this helps.

thanks for replying.

i don't get the part where using two relays would turn the motor forward and back... wouldn't energizing a relay just close one circuit? Positive OR negative, NOT both positive AND negative?

therefore wouldn't i need 4 RELAYS? 2 Relays for forward, and 2 more relays for reverse?

for example: Relay 1 supplies + to the motor WITH
Relay 2 supplying - to the motor = FORWARD rotation

then Relay 3 supplies - to the motor WITH
Relay 4 supplying + to the motor = REVERSE rotation

i would be triggering/energizing RELAY 1 & 2 with the same current by using the switch forward position, ditto with RELAYS 3 & 4 by using the switch reverse position... at least that's what i think with my LIMITED knowledge of relays... HELP!!!!

this is what i THINK i know of relays: there is a contact that when ENERGIZED(supplied with positive current) closes a switch, which completes a CIRCUIT... this circuit is INDEPENDENT of the energizing contact, which means i can assign a POLARITY to the CIRCUIT. am i making sense? so sorry.

I hope i'm missing something here coz i don't want to use 20 relays total... I hope i can get away with using just 2 relays per motor which i think is supposed to be the case...

help!!!

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85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project

Relays are like switches. They come in single pole, double pole, triple etc. This is how many circuits it can switch. Then each pole is either single throw or double throw. Single throw has just "normally open" contacts (only closed when the relay is energised). Double throw has both normally closed and normally open contacts (3 contacts with the "wiper" being connected either to the NO or NC contact). Single throw is sometimes called "form A" and double throw is sometimes called "form C". Some relay coils are polarized but many are not. You need to make sure the contact rating of the relay can handle the motor load.

Jim H is talking about using double pole relays.

You would probably be better off finding the original wiring.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Two relays per motor. Wire it this way.

Use two 5-pin relays per motor.
Pins 85 and 87a wire to ground
Pins 87 to Battery positive
Pins 86 connect to switch
Pins 30 to either motor connector

When the relays are not energized, both motor connectors are grounded.
When the switch is moved, one relay switches from ground to battery positive and the motor runs.
Moving the switch the opposite direction will reverse polarity at the motor and the motor runs the opposite direction.

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1989 300 SEL that mostly works, but needs TLC

thanks for the replies guys!!!!

moneypit,
thanks for the diagram, now i understand how using 2 relays would work.

i never thought of grounding both poles at the same time, that's the one i missed. thanks man!

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project